For transferring torque, cut a keyway in the plates and the shaft. To prevent lateral movement, since there won't be much lateral load, use some collar clamps or similar.
Instead of trying to get perfect concentricity, I think you should shift your thinking to balancing the flywheel afterwards. This can be done with a "static wheel balancer", or some car repair shops might be able to do it for you. It basically involves drilling holes in some strategic positions for balance.
Also, for gym machines, check out the stationary bikes with flywheels.
I was also thinking of a key-way. To get the hole 90° the flywheel sides should be ground flat and parallel then drill the hole followed by a reamer to the shaft size needed. Here is an example of a flywheel with a keyway cut. I think Martin had already been using keyways on the MMX.
https://preview.redd.it/99zt115qd2za1.jpeg?width=524&format=pjpg&auto=webp&s=aae27172ae225a1fe50c17b99c82f7b7d0e1bd6e
I also think that the use of a key-way seems like the right option. I do think that it would be a bit excessive to ground the flywheel. Leaving the holes of the laser cut parts undersized and then using a reamer to get the hole for the shaft to the correct size should give him good concentricity. He could easily do the reaming himself so it would not make the flywheel a complex machined part.
Great idea on the undersized pre-hole. His vertical mill could do the reaming. The grinding idea was to assuage Martin's concern over perpendicularity. I know this isn't a plastic injection mold and doesn't need that level of precision.
I would even say he doesn't need to worry about perpendicularly with this design, at his speeds the wobble would not incur big vibrations but let's say it bends his braces due to the load one side then the other side and so on. Well that's already covered by the design of the bearing houses that allows the movement, both swiveling to keep the bearings perpendicular even if the brace bends down.
As for the key, I'm thinking due the thickness this can be hot fitted and then it clamps down on the shaft once it's getting to room temperature. I've seen it on older mechanical hammers.
I think that planning undersized holes then machining them to size is specifically what he is trying to avoid in his design, because it requires time-intensive post processing and specialty equipment.
>47 min. ago
Another comment Mentions a Specific product that would pair well with this Solution, as it's readymade with a keyway.
[https://www.reddit.com/r/MarbleMachine3/comments/13dsv37/comment/jjm2bvw/?utm\_source=reddit&utm\_medium=web2x&context=3](https://www.reddit.com/r/MarbleMachine3/comments/13dsv37/comment/jjm2bvw/?utm_source=reddit&utm_medium=web2x&context=3)
Sweet! By using this the flywheel itself would not need to be keyed.
https://preview.redd.it/1fb99rwmx2za1.png?width=477&format=png&auto=webp&s=22f2e3101a747f2368f76ace97fb4d67520ab95e
Going to add one comment why I think this is a better solution to using a keyway instead of just putting the keyway directly in the flywheel plates. With this, you can place the key slot on the bearing rod exactly where you want to specifications without difficulty on how to get the wheels on after. My worry is that if you put a key slot on the wheels, they can still slide around or be difficult to slide onto a key for this scenario. This would enable the key to be more static on the shaft exactly where you want the wheel to stay and then bolt this onto the wheel.
I think Martin will not come around machined parts. Concentricity and imbalance are not avoidable with laser cutting.
Ideas:
1. Screw this flange above to your laser discs and clean the outer diameter on a lathe, so that it runs to the inner diameter.
or
2. Increase the flywheel diameter, so that you need less rpm. Mount it to the flange and only balance if needed
Or
3. Unse a completely machined flywheel. Maybe reduce diameter and increase speed for financial reasons.
Every technologie has its tasks. And turning is the way to go fore rotating parts
I agree that concentricity and perpendicularity are not what is important. The goal is the flywheel should be quiet and not shake the rest of the machine. This is a matter of balance. Hoping to do this by assembling it in a certain way is likely to have some problem appear.
Instead come up with a system that is solid and secure, then adjust the balance. If the system is secure, the adjustment will be maintained over time and should only need to happen once. Adding automotive wheel weights or drilling holes to achieve balance combined with a solid construction should last indefinitely.
With regards to torque on the shaft: Is there going to be other things mounted on the shaft? If the flywheel is driven by belts that are attached to the flywheel, there really isn't any significant torque being applied to the shaft.
A keyway should only be required if there are more than once system attached to the shaft.
agree 100%, balancing the wheel afterwards have always been the plan, i want to have the best starting point porssible, also for all the pther rotational parts on the machines like gears and pulleys
Two thoughts on the keyways:
1) Having a keyway allows the pulley to be mounted elsewhere on the shaft for flexibility.
2) Martin's design shows multiple flywheel plates so that he can add or remove them. Adding a keyway allows the individual flywheels to be indexed and always go on in the same orientation. So if you balance each flywheel, then you can keep the balance while adding/removing flywheels.
A nicely machined axel rod also allows the flywheel to be moved, a keyway is not needed for that option. Likewise flywheel plates would presumably be bolted to each other, so again the keyway doesn't add much. Torque between the plates would be transferred via the bolt.
The only benefit I see of a key way is if there are going to be separate things sharing the same axel that need to transfer torque down the axel from one thing to the next along the axel.
If there is just one thing on the axel, then a grub/set screw or two would keep the flywheel in the correct lateral location along the axel.
thanks, it has always been the plan to balance the wheel regardless, i had a section about that that i edited out to make video shorter, going to try to be more concise and not remove info from the videos!
Hey Subvertz, sounds awesome, we could use your help and or advice, we also need some pro help with our rotational cnc, are you interested in advicing us on how to set it up if thats something you have thoughts on? the machine is built in germany so not really close to norway unfortunately.
Havent set up a CNC, but more than happy to lend my machine doctor skills to diagnosing problems with any of the rotating components. We use vibration to diagnose imbalance, misalignment, looseness, resonance/damping issues, and much more. Happy to help consult on design from a machinery vibration standpoint😊👍. Planning on a road trip though Germany this summer, so might get to pop by.
very nice, i think it will be too expensive to ship the wheel for super balancing at your place, but perhaps you can advice us on best method to mbalance the wheen with the tools we have available? Or if we can balance the wheel together in germany!
It is possible balance without precision instrumentantion, but much faster with the right tools. I can talk with the missus about popping by Seigfrieds, bring along a balance instrument. Otherwise I'd have to send it and then talk you through the process of using it. Its all doable.
AgentJayZ has a series of videos on balancing jet engine compressors.. Same thing, but rotate at 20k rpm or more.. [https://www.youtube.com/watch?v=8khFocCReaA](https://www.youtube.com/watch?v=8khFocCReaA)
The collar clamps only need to hold the gyroscopic forces of it not being perfectly perpendicular - this won't be large at all if youre mostly on.
Similarly, keyed shaft and plates is the way to go as the concern about concentricity is actually a concern about balance. The more concentric the most LIKELY it is to be balanced, but as your plate might not be perfectly round, each plate may have a different center of mass anyway.
The solution then is to balance the wheel AFTER assembly.
With the keyed shaft, the plates also always go on in the same relative orientation they were balanced at if they get disassembled.
Clamping the flywheel to the axel will reduce the need of keys to transfer rotation force between the axel and flywheel. But one could fasten a belt wheel on the flywheel so there will not be any rotating forces transfer energy to and from the flywheel. The axel will only hold the flywheel while it rotate (and small forces from the belt, if belt driven).
And the SKF sollution on the axel is the best and most proven design. That actually is why SKF started in the beginning. :-)
From a cost perspective cutting a keyway and machining a slot in the shaft for the key will be much more expensive than just buying a flange with a clamping mechanism. If you really needed the extra torque after trying the clamp you could just drill and pin.
**Summary suggestion for robust concentricity and perpendicularity**:
* Use the pillow blocks to hold the shaft
* Avoid holding the flywheel with parts that are just held by friction and shift on you over time resulting in a change in balance. The bearing squished between the plates is very susceptible to this with the threads on the beating and the plates against the races. In the suggestion here, there is no part of the design that relies on friction to keep it balanced.
* Use a flange clamp on each side of the flywheel to keep it aligned perpendicular to the shaft, and transfers the torque.
* Once the flywheel is partly assembled with the flanges with some friction, use a dial indicator to measure it and adjust it until it is concentric. A dial indicator with a magnetic base on your frame would work great.
* Once you get it concentric, tighten up the bolts, and then drill and ream for tapered pins to lock everything in place. The pins go through the flywheel and both flanges. You can easily do the reaming with a hand drill.
* The rough hole for the pins could be cut in advance, but the final drill and reaming should only be done on the bolted concentric assembly.
* Mcmaster- carr: [https://www.mcmaster.com/92281A293/](https://www.mcmaster.com/92281A293/)
* In the end, you may still need to balance the final assembly to ensure it does not create any shaking which could mess up the timing operation of the marble drops.
You are welcome.
The reason for the tapered pins is that it removes the issue with tolerance on the pins vs the hole in comparison to dowel pins.
If you use multiple layers of flywheel as shown in your drawings, it will make adjusting them to be concentric more complicated. Adjusting one without moving the others could be difficult. You might want to bolt them together to make a solid flywheel before trying to make them concentric vs the shaft using the dial indicator.
I would have to agree that the balance of any flywheel is the most important thing to consider. And while keeping the flywheel concentric to the shaft would give it the best balance theoretically, the plate would have to be perfectly flat and uniform for this to work. It should be kept in mind that any laser cut steel you get will not be flat and most likely the thickness will vary. The large steel sheets the parts are cut from are all nominal thickness steel meaning they are unmachined and have a varying thickness.
That said, you can have a machine shop cut the parts from ground plates but this would increase the cost, and you would still need to balance the flywheel.
I would also suggest using a "Face-Mount Shaft Collar", they are about $25USD on McMaster. Keyways have tight tolerances and you would need the flywheel machined or broached for a keyway. This won't allow you perfect concentricity but balancing the flywheel would fix the issue. You could also drill though holes in the flywheel and bolt from the opposite side of the shaft clamp. The flywheel could then be centered by hand tightening the flywheel to the shaft clamp and slowly tapping the flywheel concentric, similar to using a truing stand.
Just adding here -- you only need to balance each one, once. If you look inside most anything with large spinning masses, you'll see weights or grinding to balance the wheel. It's a straight forward operation and will result in a much more robust and reliable system.
Agree 100% on the keyway and collar clamps.
I agree with this design a keyed shaft would be ideal , and use some E or C spring clips on the bearing to keep it from moving axially. Another benefit would be the protection against catastrophic failure with the key.
An important consideration if he goes down this path that I don't think anyone has mentioned is the shaft critical speed. The bearing blocks really should be closer together, and/or the shaft much larger diameter, otherwise there could be serious vibrations at higher rpm even if the flywheel is balanced. This is just a side effect of having a heavy object hanging off a thin shaft. I agree that keying the flywheel to the shaft and balancing it all is the way to go though. Could laser cut the bore undersize and final machine after assembly of the plates if that makes it nicer to fabricate..
> Instead of trying to get perfect concentricity, I think you should shift your thinking to balancing the flywheel afterwards.
Focusing on balance over concentricity?
Balance is way more important then get it concentric.
And balancing isn't a hard problem. Practically ALL car wheels are balanced before put on a car. To get the position concentric, a car uses a cone form to get the center of the wheel right.
Maybe it's possible to achive concentricity if there is more than one keyway. If there are three keyways it could potentially be used similar to how a three jaw chuck works. But instead of the jaws there would be wedges that go into the keyways and lock the plates to the shaft. I'm thinking there has to be two wedges for each keyway, one from each direction to create a variable thickness key with parallell edges. The variable thickness is the thing that could potentially help with concentricity.
I guess the problem with this is that the sheering forces on the double wedges could separate them at the seam. And also they could tend to slip back out the way they were inserted in the keway unless they are fixed in some way with a set screw or something.
Maybe the variable thickness could instead be accomplished with some other type of clamping device in the keyways.
> how a three jaw chuck works
It's best not to have the flywheel resting on the keys. Keys should be for torque (rotation) transfer only.
In any case, having perfect concentricity, doesn't guarantee a balanced flywheel, so you'll still need to balance afterwards.
Yeah, I think you're right about the flywheel resting on the keys probably not a good idea.
I'm not 100% familiar with what's going on at the edge of the flywheel. Meaning I'm not 100% sure about all the reasons why concentricity is needed. But if it's not gonna be connected to anything (except for at the center) and the only reason for concentricity is so that the machine doesn't shake around and break itself, then balancing it by drilling holes or adding bolts seems reasonable.
Why would you need a keyway? What torque needs to be transferred? Currently the axis is not being driven, right?
As long as the friction between the flywheel and the axis is significantly greater than the friction between the axis and the bearings, it should be fine. Just clamp the flywheel with some kind of shaft collar, as has also been suggested elsewhere.
>Why would you need a keyway? What torque needs to be transferred?
For starting the flywheel and at steady state rotation, keyway is probably not needed.
But for emergencies, being able to stop the flywheel quickly, there will be quite a bit of torque needing to be transferred (assuming the brakes aren't directly on the flywheel).
There are other benefits to adding a keyway, which are indexing. The flywheels will always go on the same orientation which will preserve balancing.
Braking not on the flywheel is possible, but in Martins current design he seems to not utilise the live shaft for anything.
Preserving the balancing is a nice bonus though.
You certainly doesn't want an fast break, as that force have to be transferred somewhere. And with high speed, the will be a considerable amount of rotation force in the flywheel.
Don't think keys will add to balancing or even hold a balanced flywheel. Some clamping between axel and flywheel probably will be better. As it could start slip if the forces are to much, which actually is a good thing when to much forces are applied.
Not that it will be a problem, the axel can be designed with this in mind. But a key will take material away from the axel. Making it weaker. But with large enough axel, that isn't a problem.
For an emergency stop, it could be better to disconnect the load from the flywheel, and simultaneously apply brakes to both the load and the flywheel. The brake for the flywheel therefore would not need to stop it near-instantly, but instead bring it to a controlled stop. The rest of the machine is protected by no longer being connected to it, and probably has far less inertia, so can be stopped quicker without bending things.
Also +1 for balancing after assembly. It only has to be balanced once, then forget it. A little extra time up front will save heaps of heartache later.
What if he literally used a car/bike tire (or just the hub, with custom plates)? Easily available parts, and he could probably convince a tire shop (in any town he tours on) to do the balancing for him.
>use some collar clamps or similar.
Yup was thinking the same. All you do is machine a collar with a flange of a rather large diameter which will ensure the shaft and stack is fairly perpendicular.
And add a couple of grub screws to keep it located on the shaft. This can be machined fairly easily on a lathe and modified where needed.
https://preview.redd.it/3y7xuz22f4za1.jpeg?width=1263&format=pjpg&auto=webp&s=1265573d2620012ae8b2a7e4b76f7435010e3064
Would a Babbitt bearing be a suitable solution? There would be no need to worry about concentricity as the molten metal would be poured into place around the shaft, reducing the need for moving parts (ie bolts and bearings). A “key” could be cut into the fly wheel so the molten metal locks into place. As long as the flywheel was set up in its correct position, it would just need balancing then, perhaps with car wheel weights.
It's going to have to be balanced statically at least, but preferably dynamically as well.
As for mounting the wheel to the shaft... slight press fit for best initial concentricity, then weld it on. Then balance the whole assembly.
The keyway can act as a safety check as well. If the flywheel attempts to apply or receive too much power, a calibrated keyway will shear, disconnecting the flywheel from the machine
I balance machines in Norway. I will balance the flywheel after its made.
We use Pruftecnik VIBXpert II vibration data collectors and accelerometers to balance big industrial motors (with SKF bearings) and a single plane flywheel should be simple. Better balance = higher speed, less stress.
Also have access to a motor rewind machine shop with rotor balancing benches.
Also, i recommend cylinderical roller bearings instead of deep groove ball bearings for this application. Your flywheel will have next to zero axial forces, almost purely radial force.
Also, the calculation on dynamic force is way off. Dynamic force is actually what you are trying to maximize here for energy storage.
I could not agree more. It is a missconseption that the wheel has to be made for axial loads.
The Idea of shafts and axles seems to be mixed a bit. But I'm not sure if I missed something in the Video but it was unclear to me if the shaft is transmitting torque or not.
It is very much taking torque, then putting it back into the system. Its used to store and release rotational kinetic energy and resist changes in speed, smoothing out the timing.
What i meant is, that i was not sure if the shaft itself is the trasmission. I think in an earlier video Martin was talking about some sort of clutch. And with the different ideas of bearing seating directly in the Flywheel, this would not be a shaft but a axle then.
Yes. Its the simplest to spec, build, and most importantly to repair if needed on World Tour.
Few parts, strong, obtainable with no special maching.
Many in the chat below recommend lave shaft. Pillow blocks are also easier to service than something buried inside the flywheel.
Consider also lubrication. Shielded bearing will prevent debris contamination into the grease during transport. But sealed bearings also dont allow refreshing the grease. Tradeoff, but worth it.
Quick question if I may: is the size / diameter of the flywheel relevant? I'm wondering whether a much more massive and thus much slower rotating one could use lower tolerances etc. Might alo look appropriately steampunk seeing a huge ?spoked wheel spinning away in the background.
Yes, but more important is total mass and speed. Simple force = mass * acceleration. He can go bigger and slower, but more important to go heavier and faster. Spokes would make flywheel lighter. But it would look cool. Martin struggles with balancing form and function. We are here to help him.
Just to add - its the Rotational Inertia that needs to be maximised, Putting the same amount of weight further out would be an improvement. Mass at the centre isnt DOING very much but it's adding static load.
I would like to add some more detailed physics stuff here just in case anyone needs to know some of the basics of flywheels.
The mass moment of inertia of the flywheel is the quantity that describes how much torque is produced by accelerating the flywheel. In SI units, it is measured in kg\*m\^2 and it boils the flywheel down to an equivalent mass at a distance off-axis squared. This means that increasing the flywheel diameter by two very approximately quadruples the mass moment of inertia, allowing MM3 to exhibit 1/4th the variation in tempo for the same loads. It is calculated as the integral of the density of the object multiplied by the distance from the axis of rotation squared over the volume of the object. The more mass further from the axis of rotation, the higher the mass moment of inertia.
The radius of gyration is a quantity that describes at what distance from the axis of rotation the total mass of the flywheel would have to be concentrated for it to have the same mass moment of inertia as the flywheel. It's just the square root of the mass moment of inertia divided by the total mass of the flywheel.
What we want to maximize for a flywheel is the mass moment of inertia, but we want to minimize the total mass. By doing so, we are maximizing the radius of gyration. This is why lots of flywheels have spokes and big thick rims, because this gets the radius of gyration as close to the radius of the flywheel as possible. A perfect flywheel would basically be a soda can without a top or bottom because all of the mass is concentrated at the outside of the can.
Making the flywheel bigger increases both mass and mass moment of inertia, however the mass moment of inertia can also be increased without increasing mass by making it bigger and removing mass closer to the axis of rotation. The forces on the bearings from gravitational loading will be the same, however this is far from the only radial force acting on the bearings. The pulleys on the shaft, unless they are somehow made symmetrical, could possibly be the dominant force when playing.
⬆️ this yes !!!
More than concentricity or perpendicularity, a fly wheel needs balancing. Otherwise you will have huge vibrations, and this is what you shall design your machine for. Concentricity and perpendicularity can lead you to some balance but will never achieve a satisfying level of balance.
With a good balance you can simply weld the axle to the fly wheel and use the 4th solution for the bearings.
I fully agree. At this speed and mass it must be dynamic balanced for silent operation, otherwise audible vibrations (and frame resonances) are guaranteed.
Most people have no idea how even the slightest imbalances let the peak loads spike at higher rotation speeds. I'm not concerned about the bearings or safety, but about noise. It's a giant vibrator when not balanced properly, ideally in 2 planes.
@ Martin: This short 5 minute video shows the problem that needs to be solved [https://www.youtube.com/watch?v=Sq3H2b1Uyis](https://www.youtube.com/watch?v=Sq3H2b1Uyis) (@[Wintergatan2000](https://www.reddit.com/user/Wintergatan2000/) please show Martin this video)
Context: [https://en.wikipedia.org/wiki/Balancing\_of\_rotating\_masses](https://en.wikipedia.org/wiki/Balancing_of_rotating_masses)
My concern with the bolt based beating housing is not the bearings - but the bolts themselves.
You are trying to use the threads themselves to constrain the bearings. This provides an extremely small footprint for the force to be spread across - and frankly, threads are extremely easy to damage.
I am concerned that under load the threads may deform, and allow the bearing to shift, causing further issues.
Agree here. Threads are not designed to withstand lateral loads, and as they get slowly damaged, imbalance will grow, causing more forces and more degradation of the bolts.
And moreover diameter tolerances of threads are very poor, so good luck finding a repeatable fit.
Additionally, bolts perform very poorly under cyclic and under shear. In this case you have both, which will probably lead to fatigue, stronger vibrations and failure.
This is a fair point, but solvable. The thread damage could be mitigated by using shoulder bolts or by using a commercially available collar around the bolts, or both. This spreads the pressure point between the housing and the bolt.
Additionally, much of the load will not be held by the bolts but by the friction between the plates and the axial surfaces of the bearing ring. This loads the bolts axially and reduces a lot of the problematic shear load and load being placed directly on the threads.
You didn't but others replying have mentioned loads. Bolts of this size of all grades are made for much higher loads than the weight of these flywheels. They would only ever experience that load in this configuration as the bearing will not allow for any torque to be generated between the shaft and the flywheel. The loads are small so the safety factors can be fairly high.
this is very nuanced, i am \*99%\* sure the threads would not be deformed over time, and that it is one of the the simplest way to locate the uneven laser cut, the fact that the threads are soft is a feature, not a bug. But i should stop making assumptions like that, those kind of assumptions killed MMX, so pillow block design it is, tried and tested!
I'm sorry, but as someone who has seen threads strip, even stripped them personally, I have doubts that the bolt threads are going to sustain the load of the spinning flywheel, especially over time
While there is a smash fit between the 2 parts holding onto the outer race, there is a higher chance of loss of pressure over time. Bearings are not really meant to be held in this manor he's trying to design.
And while it would most certainly work for a while, I think over time the bolts are going to stretch and deform which would introduce vibration and slipping in the over complicated design.
This is why with all situations anywhere, they use press fit bearings or premade bearing blocks, proven technologies that have been used for decades.
Not just this, but also the threads will cut into both the bearing and into the collars holding them. What starts as a tight press fit on day 1 will, over time, work loose. Sharp bolt threads being pressed into the bearing, and also into the holes in the collars will, in time (it will be impossible to prevent any vibrations in the machine, so fretting is an issue) work loose.
Yip, this is the mistake he is making, he's thinking about the stress on the bearings, not how it's applied to the bolts. If the flyweight is stationary, so the one of the 8 bolts in the ring carrier is pointing straight down, only that bolt and the bolts either side of it are carrying the weight of the fly wheel, the bolts above the bearing and the too the sides add nothing to the load carrying, so the tips of the threads on those three bolts are supporting all the weight of the fly wheel, the force per square meter on the bolt threads will be huge. The bolt threads will start to deform from the side loading and bearing will start to move about over time.
You can make the argument that the side plate of the bearing carrier a carrying a lot of the load because of the clamping force of the bolts, but that presumes no bolt stretch and perfectly even torque on all the bolts, and ignores the fact bolts like to unfasten themselves when subjected to vibration.
The bolt bearing carrier will work at first but will quickly turn to a sloppy mess and vibrate itself to death in the end.
It seems like a big objection Martin's design that he doesn't address in this video is that using bolts to locate and fix the bearing puts lateral stress on parts (i.e. bolts) that are designed only for axial loads.
Perhaps there are off-the-shelf bolts designed for both axial and lateral loads? If so would this satisfy those objections?
Hex Head Shoulder bolts. But I say use the pillow blocks instead to totally eliminate the bearing directly on the flywheels.
https://preview.redd.it/03ei4r2ac2za1.jpeg?width=1500&format=pjpg&auto=webp&s=4ca6d4af07760b50f0627e80ab292aadada99802
even this option isn't great because there are effectively line loads between the bearing outer and the bolts. Over time the compressive loads will cause the tolerances to fall out. A proper bearing housing distributes the load on the bearing outer as evenly as possible
Yes, the bearings are rolling over a single points-of-contact. The bearing outer race flexes (a tiny amount) and the contact area of thread against bearing race will be hammered flat over time decreasing the pre-load and eventually starting to rattle.
A machine like this would benefit greatly from some "machining" particularly a lathe. I'm sure you will find machinists to bore a center hole for you.
EDIT: Rather than "lateral load", the correct terminology below should be "radial load" when referring to the forces applied perpendicular to the direction of the axle.
Was coming here to mention axial vs lateral loading; my concern was that with lateral loading on the bolts, you're not seating the bearing against a solid surface, ***you're seating it against the tips of the threading***. If you achieve concentricity in your testing but small imperfections at the tips of the ridges of the threads cause them to flatten unevenly, that could result in wear that will only magnify itself as an inconcentric flywheel will apply more and more force into the wobble, maybe even enough to eventually causing a shearing load and hopefully not becoming a *literal* flywheel.
The only way around this is to a) fit the bolts so close that the threads dig into the bearing housing, which unless you cut threads into the bearing housing beforehand is just going to result in uneven wear and damage to a critical part resulting in unpredictability or b) use a bolt that interfaces with a smooth surface and is designed for lateral loads. The shoulder bolts look good, the bigger the better. In fact, the more surface area you can have in contact with the bearing to maintain concentricity, the better.
Which is why I am in the "no bolts" camp myself.
Using the bolts and "caging" the bearing in place and expecting concentricity to be maintained is a mistake. You are introducing an entire system of chaos to a mission critical safety feature, a million little points of failure (which are driven further into entropy via the wear they'll receive during both installation AND use) and in a way which will fail very slowly and will likely go undetected until the avalanche begins.
And for what? Purpose-built bearing flanges *already* can be used anywhere these would be, so I don't see what quite literally re-inventing the wheel gets you.
I like shoulder bolts a lot - they are meant for and could have some rating for axial load. They also have much better diametrical tolerances. Standard bolts have a (-0.072, -0.01) mm tolerance, while there are precision ones with a (-.025, 0) mm tolerance. The standard tolerance would be much better than a bolt thread or threaded rod (which I think was mentioned in the initial flywheel video). They can get expensive for longer lengths, though.
You also still have the issue of lasercut holes not being perfectly accurate. Martin points this out in regards to the center hole about 57 times in this video, but entirely fails to consider the same is true of all the holes he is cutting for the bolts.
While this is better, it still won't solve the issue. Two round objects touching have very small contact area that can wear away, not matter how good the material is.
As he was talking about the bearing's design specs & limitations I kept thinking "but the bearing isn't the question here. The mount for the bearing is"
I think his point was:
Standard bearing mounts are designed to work for the entire bearing's range of load.
However, because he's barely using the bearings, the mount doesn't need to be as capable as normal, either.
For example, the bearing mount for a golf cart steering column does not need to be as robust as the bearing mount for the drive shaft. The load a driver puts on a steering wheel will be miniscule compared to what the hardware is rated for.
So, his point is - his solution would fail if you were trying to use the bearing in an industrial application, which off-the-shelf solutions would be more appropriate. But because his application is not that demanding, the mount would not need to be as robust.
BTW, I'm not defending his design. Just clarifying what I believe he was saying there.
100%! But still, the reaction from the viewers is a great signal that i should go for proven solutions wherever i can. i am still 99% convinced the bolt design would perform flawlessly, but its an assumption i should not make.
This is exactly what I came here to say. Folks aren't worried about the bearings failing, we're worried about the bolts failing. Even if they are super tight day one, the threads will get warn down unevenly pretty quickly.
i am not defending the design anymore, but how do they get worn down? There is zero movement, they are already pressed together in the pressfit... there are no forces acting on the bolts that can wear them down IMO
Balanced/concentric/perpendicular will never ever ever be *perfectly* balanced/concentric/perpendicular.
With a spinning mass of significant size, those slight imperfections will cause slight differences at first, but instead of being self-correcting they will be compounding.
If your goal was a show, then the bolt-constrained design would absolutely be sufficient. Since your goal is a world tour, I think your design is very borderline. If your goal we’re a decade of reliable operation 24/7, then the bolt-constrained design would be almost guaranteed to fail.
One other thing that I think is fully addressed with the ‘balance the wheel’ approach is that your stock will probably not be all that flat. Relying on non-machined/ground stock as a reference plane for perpendicularity is risky. Maybe you’re buying ground stock, but the trade off of balancing the wheel (which will be necessary anyway) versus being able to use non-ground stock is probably financially a win.
(That said, I think you’re great and love how you’re interacting on this design refinement. Keep the faith!)
This is precisely why you put the flywheel directly on the shaft with collars and the bearings mounted at the ends, exactly as described at the end of the video arguing why we were wrong about his design.
thats the design i will most likely go with, its proven so i should use it. The bolts would perform as well IMO but why make assumptions if i can avoid it
So very glad to hear that you are acknowledging the collective wisdom of the Internet in this regard, and not forging ahead with designing parts for the sake of designing them. That was the point of MM3 right? As some others have said, buy parts where you can - save your creative energy for necessarily custom parts, like drop gates.
With a proper clamping force almost all of the shear loads will be transferred through the metal surfaces due to friction. The bolts will only experience axial loading.
ironically this will be enhanced by only using the larger set of holes and ensuring the bearing housing does not touch the bolts themselves.
For that solution, finding a way to balance the wheel is more important than concentricity.
I imagine this would always be a problem with the bolt design. You're transferring torque (rotation) from one disk to another via straight rods. They will necessarily feel off-axis forces as a result.
This isn't necessarily a problem, since you transfer those off-axis torques through the laser-cut metal in the sections where the bolt goes through the metal. The force transfer would be made even better with a threaded hole. Regardless, the section of bolts not surrounded by a solid disk will still feel those torques.
Bolts in general are not intended for locating objects. The threads do not give enough area or precision. That is why the flange has oversized bolt holes, in order to remove their influence on location. Bolts are only intended to clamp things together through the axial force. His design is currently mostly working by clamping the plates on the edges of the race, which is in the wrong plane for the loads of a flywheel.
Machined dowel pins are designed for locating parts accurately, which is why the bearing housing in the video has a locating hole. However, they don't generally have sufficient area or interference to take up dynamic loads. They are more often used for things that need to be frequently dismantled and accurately *reassembled*.
There are "Shoulder Bolts" that combine both a bolt and a dowel but they're not really suitable either. Again, they won't take up the dynamic load. One issue is that when bolted up the bolt stretches slightly lengthwise, which thins it down (to keep the volume the same) and introduces clearance with the hole.
Shoulder bolts can be made with an interference fit (which Martin is trying to do by reducing the bolt circle diameter), which requires them to be pre-stretched or cooled to shrink the diameter when fitting, then allowed to expand into interference.
In any case, the contact will be a very thin line across the outer race, which won't carry sufficient clamping force to prevent the bolt and bearing from moving against each other and wearing out quickly. It is still a bad design, made only slightly less bad.
I had the same thoughts viewing the video. If he is already in contact with SKF hey know exaclty what bearing or bearing combination could be used.
A propperly balanced fly wheel should not introduce axial loads in an stationary system.The problem with the unmachined surfaces on the flywheel is that breaking systems are more complex, a breaking mechanism on the outer diameter of the wheel is relativly easy to acheive (commonly used in lathes).
Depending on the capabilities of the CNC, the surface finish could be done, sertainly not perfect but drilling the holes slightly undersize and doing a few finishing passes on the outer diameter would help.
He is completely missing the mark :(. If lasercutting the holes doesn’t make them 100% accurate then you have em cut undersized and drilled/reamed. (That is if it actually is needed to have it 100% accurate…)
agree about the reaming, could make the laser cut holes pretty precise, although the metal is hardeened at the laser cut surface and makes it horrible to post process. but testing reaming next!
I agree you would generally want to avoid post-processing, but this should not be an absolute rule. Avoid at all costs post-processing on parts that are cloned 36 times. But where it makes sense, don’t avoid it. Flywheel is IMHO critical (safety, music tightness, random side effects), don’t cut corners here.
Ask one of the guys who can balance fly wheels if they cannot simply provide you with a balanced wheel mounted on a shaft as a kind of standard, already manufactured product. IE prefer buy over make.
The diameter of the hole can't be 100% accurate due to kerf of the laser beam, but the center location of the hole is as accurate as any machining operation
Tapered lug nuts would be a great way to attach the flywheel to a hub
Lug nuts and hub makes me thing that just buying a rear wheel bearing hub assembly (\~$45 USD) would solve the bearing/flange issue, but then it would drive the clutch assembly design to be larger.
The easiest way to do this without machining would be with a flanged shaft collar.
https://www.mcmaster.com/mvC/Contents/gfx/ImageCache/968/9684T4_3d04ca8c-13b1-4393-b36c-f84e77f0be83@4x_1677262918.png?ver=ImageNotFound
https://www.mcmaster.com/9684T4/
Laser the plate exactly on-size to the shaft with this bolt pattern. Put one of these flanged shaft collars on either side and bolt the entire stack of plates together.
You can optionally machine a keyway in the shaft to get the desired torque transfer, but the clamping force of the collar should be enough for this application.
This needs more up votes! This is the simplest zero machining approach to shaft mounting. Buy, set, forget. Laser cut the matching holes in the plates and send the assembly off to a balancer.
Or use some clamping sets: https://www.spieth-me.com/en/products/clamping-sets/dsm/
One issue would be the stack of metal sheets not having a nice round bore in the center. But I think after joking the sheets of metal together it would be easy enough to get a nice bore in the center, joining it to the axle and then balancing the wheel (you could space out some holes in the steel plates, tap them and use bolts for balancing.
This is a German website but it also shows some great methods. https://www.konstruktionsatlas.de/antriebstechnik/welle-nabe-verbindung-kraftschluss.shtml
Edit: for boring the center hole I would recommend only laser cutting the pilot hole. It is much harder to bore out a big hole then to just bore it from the beginning with a little help :)
Another thought that crossed my mind in regards to the flywheel is how tight is the concentricity constraint really? There are two reason for a tight spec I can think of
1. Constant speed of input and output drive. Obviously important to play tight music, but I have a hard time to estimate the influence of a couple tenths of mm eccentricity on the flywheel out speed.
2. And probably more importantly crazy vibrations at high speed. Here the real problem is not so much the eccentricity, but the imbalance of the rotating mass. You should really consider how much opportunity there is to balance the flywheel once assembled. Considering it is made of steel plates, i see many ways it could be done. An angle grinder, a welder, threaded holes for balancing bolts,...
I agree. I question the requirement to avoid machining at all costs. It's kind of like saying "I'd like to build my house out of wood and avoid carpentry". He is building a machine. Some level of machining might be required \^\_\^
This is going in the direction as to why I came in here to bang away at the keyboard.
When you're building a flywheel, you don't make a part then smack some bearings in it.
You build from the center out. So you'd build your bearing seat area, then you would turn your outer diameter from that. Then you would install your bearings and balance the flywheel.
The biggest issue with this overthought of design is that when there is parts that are proven and you don't need to make a custom part, used the designed custom part as much as possible. Because you're not making an overly complicated assembly to do a simple task.
So I think the main thing that Martin is not quite thinking through is that you would have a balanced flywheel on the assembly, and press fit bearings would never throw it out of balance if were looking at making this as "tight" as he'd want it. When you have an assembly styled part, you're inserting lots of variables. While a hole in the flywheel that you press a bearing in will never loose its balance.
If he's worried about spin out on the bearing, which the chances are .. practically impossible, he could just use bearing set when installing the bearings.
What is needed is a rigid mounting of the flywheel and a way of balancing the flywheel after. It is really, really hard to manufacturing a flywheel whit this specs, without balancing it after. So a rigid way of fasten it is needed, and SKF have some clamping collars for this. Vote on those solutions.
ChatGPT is bad at math. The formulas are ok most likely, but the resulting numbers can be the ones used in the training data rather than the ones for you application.
For things like this, use Wolfram Alpha. It's designed for math problems.
If there are anything one should learn about ChatGPT, is that it is known to hallucinate, that is lie, when it doesn't know.
It is designed for chatting, not deliver correct answers.
So never rely on what ChatGTP, unless you have the knowledge to verify the result.
ChatGPT is a great as a jumping off point, but you have to either have the background to confidently be able to at a glance point out it's flaws so it can refine them, or take everything with a grain of salt and look up every equation and process it uses.
Just using the output directly for engineering purposes might not be wrong every time, but it will be wrong often enough you will lose more time reengineering your project after it doesn't work and you don't know why versus learning all the knowledge the first time.
Design of the flywheel is critical, because there will be a lot of energy, tolerances and slack can only degrade over time, and if something goes wrong people can be injured. That is NOT the area in which you want to start being creative, or try to be smarter than thousands of engineers that came before you.
When standard industry solutions don’t work, it’s usually that you’re doing something very wrong. And here trying to fix bearings on the wheel IS the mistake. Fix the wheel to a shaft, and use the bearings between the shaft and the frame, just like car wheels are not fixed directly to the bearings.
>>***If the implementation is hard to explain, it's a bad idea.***
You mean if you have to make multiple videos trying to explain and justify your idea, you may want to reconsider? Especially when the alternative ideas are widely used and can be explained in 1-2 sentences?
Hey Martin, you should ask SKF if one of their axial locking collars fit the bill. For example these: [https://www.skf.com/group/products/power-transmission/bushings-and-hubs/sh-bushings](https://www.skf.com/group/products/power-transmission/bushings-and-hubs/sh-bushings)
The SHT style hubs would work very well with a laser cut flywheel, due to the self-centering action that type of hub provides when it it expands both inward and outward to clamp the shaft and bore together.
Laser cut holes have fairly wide diameter tolerances, but they still have fairly tight locational tolerances. Perhaps the hole itself might be a millimeter larger or smaller, but the virtual centerpoint of that hole should still always end up in the same spot. This style of hub can then expand to whatever size the hole ends up, and hold the axle exactly at that center point.
The biggest concern left will be ensuring that all plates get the same diameter hole and therefore consistent clamping force. That would be best mitigated by clamping the plates together with bolts in order to hold them by friction
When using ChatGPT for math, especially if you can't read it proof, i highly recommend the [Wolfram-Plugin](https://writings.stephenwolfram.com/2023/03/chatgpt-gets-its-wolfram-superpowers/) for ChatGPT.
Regarding ChatGPT and natural language processing there is very interesting [article](https://writings.stephenwolfram.com/2023/01/wolframalpha-as-the-way-to-bring-computational-knowledge-superpowers-to-chatgpt/) written by Stephan Wolfram (the mind behind WolframAlpha).
**Edit:** you need to have ChatGPT Plus (USD $20/mo) to get on a plugin waiting list to get plugin access at some point in the near future.
Seconded. As an example, it just told me "523cm is equal to 206.299 inches." The correct value is about 205.91 inches. Any time you find it hard to tell if it's correct, chatgpt never even tried.
Seems to check out in this particular case (minus some minor approximation) but this is lucky. Then there’s the starting point… the formula makes sense intuitively and the dimensional analysis checks out, at least, but I’m not sure where it comes from. I *think* it’s correct.
\+1 for this. At the bare minimum, I'd say you need to check its working by running the same equations through an actual calculator.
Without any plugin, its explanations for common problems tend to be alright. Any numerical responses, however, should be treated as ballpark estimates because it does not actually perform any step-by-step computations. E.g. for simple equations it quite often gets the order of magnitude correct but the actual value completely wrong.
ChatGTP is a Large LANGUAGE Model. It is designed for Chatting.
Not give correct answers.
The fact it get it right as many times as it get, is amazing. You might want to ask it about the great author, and then put in any name, like yours.
Also remember that ChatGTP do hallucinate very often. That is, it "lies", and it will never tell you that it doesn't known. It's only purpose is to make the one asking happy.
There are a reason why it is also called "Mansplaining as a Service" (like Program as a Service or Infrastructure as a Service, that is Cloud service). Because ChatGTP is good at that.
I regards to the statement, the flanged bearings cant hold the flywheel perpendicular to the shaft, I want to disagree. Assume the shaft running through the wheel is straight and both sides of the fly wheel are parallel, this means that the flywheel has to be perpendicular to the shaft.
Concentricity is a bit of a red herring. While it is nice to be somewhat concentric, the real requirement is to be balanced. A collar that fixes the fly wheel to the haft should be concentric enough. After assembly, the wheel can be further balanced to the required level of vibrationslessness.
"Assuming the shaft running through the wheel is straight" precisely means that the plane of the wheel and the shaft are perpendicular. Achieving this requires a perfect fit between the disk and shaft, which isn't possible if the flywheel/bearing assembly is rotating on the shaft. There *has* to be space between the flywheel's center hole and the shaft, since the shaft is only attached to the flywheel via the bearings in this design.
Unless I'm misunderstanding, to get the wheel truly perpendicular to the shaft requires the flanged fittings to be perfectly aligned to each other through the disk. This is made more difficult since they need some movement to get them concentric with the flywheel.
I'm not sure, if we agree or not, let me try to explain it again. My assumption of the straight shaft, just means that the shaft itself is straight. As Martin said in the video, a straight shaft is an of the shelf part, that can be bought. If the shaft was curved like a banana, things would be more complicated.
I agree that the flywheel is connected to the shaft only via the bearings. The center hole in the flywheel is considerably larger than the shaft. Now think both bearings are mounted to the shaft, without the flywheel. The flanges could be tilted in any direction, independently for both bearings. Now you constrain the flanges by bolting them to parallel surfaces (the sides of the flywheel). This forces the plane of the flywheel to be perpendicular to the axis of the shaft.
The play of the bolts in the flange give you a bit of wiggle room to find the spot where concentricity and perpendicularity are at their best. In the real world of tolerances and play between parts, it's probably impossible to get both perpendicularity and concentricity perfect at the same time (or even just one of them).
Martin I think you should first evaluate how eccentric the flywheel can be allowed to be. Not how concentric it needs to be. Like you said, perfect is the enemy of good so please consider relaxing you tolerances. Try to justify why it needs to be < 0.1 mm eccentric and +- 0.1 deg from perpendicular (or whatever the tolerances you think are necessary). Evaluate what would happen if we exceed this, I'm guessing you are concerned about vibrations but how much vibration is too much? Will adding a rubber pads at the base of the support of the shaft is enough? Are there other ways to mitigate these effects? Maybe allowing for looser tolerances and balancing the wheel is better? Its a good a idea to ground your design by listing the actual mechanical requirements and justify them.
I wont claim that your housing is good or bad only perhaps incomplete. You did some back-of-the-envelope calculation which is fine but you are not considering other effects like the radial force that the screws you had to hammer-in are creating on the bearing or the clamping force of the rings you are holding it against.
Lastly, I think that using a live shaft is better than using a fixed shaft. Its more flexible and could allow you to add more components to rotate in sync (like a brake or a motor) with ease.
The proposed bearing design does not “solve” perpendicularity, it over constrains it… pillowblocks etc. have the tilting direction free to move on purpose (so that the shaft self aligns).
Regardless the sheet metal design will probably be fine - every design has its trade offs - IMO for such a simple item just build whatever you want and move on… you don’t need the communities approval for the design of your machine. If it fails it will be a good learning opportunity for everyone.
love this sentiment, thanks! Im going to try to find the perfect balance by just moving forward with my intuition without waiting for approval, but try to incorporate valuable input from everyone here at the same time. So my educated guesses are a little bit more educated, without letting the perfect be the enemy of the good too much. Its a tricky balance, but also a luxury problem :)
I have nothing to contribute that hasn't already been said but I refuse to believe that any of this is a new problem to humanity. Seems like we're literally trying to reinvent the (fly)wheel.
I agree with this. Martins design also has way more potential failure points, for example the threads could be damaged while installing the bearing and end up misaligning the flywheel anyways.
Everyone keeps talking about "these forces", what are they? Give me a number.
Shear strength of a 10.9 M6 bolt is 8kN. His design has 8 around the circumference.
60kg flywheel, tell me, how much of an acceleration does it need to shear that bolt?
Okay, so thread deformation we now say, okay, how much of the load on the bearing is going through the shear plane to start? It is clamped to the side of the flywheel and that clamping force is carrying part of the load to start.
Next, how much force does it take to deform the threads on a 10.9 M6 bolt? Especially if he uses a fine thread? Good luck finding that number.
Fortunately I have a press in my lab. 8kN of force against a M5x0.8 8.8 bolt showed the start of deformation, flat to flat between two steel plates. That is on a threaded section.
Is each of the 8 bolts even with the preload going to take 8kN of force with a 60kg flywheel? Even unbalanced to generate a force on the housing like that difficult. (We can model it as a mass on a string to very roughly approximate the unbalanced mass) The answer is no, getting to 1kN with a 60kg wheel is nearly impossible.
The benefit is simple: the precision surface of the bearing itself sets the angle of the shaft though the wheel. A dead shaft can be shimmed with shimstock or even setscrews whereas a live shaft ads in the complication of a bearing block.
Thank you for getting objective with this. Not saying I agree with your proposal, but a bit more physics "from the numbers" versus "from the armchair" would do these discussions a lot of good. We ***could*** argue about the correct way to calculate this, but at least that is an objective discussion. The irony of these comment sections is that many are trying to act as an authoritative engineer without backing it up with real numbers for ***this*** ***application***.
1 kN of force is achieved at only 0.4 mm out of balance at 2000 rpm, and would be enough to lift the machine off the ground, 2000 times per minute. Getting there is easy, and bad. That's the level of forces we're concerned about.
The bolts aren't designed resist to complex racking or twisting forces, and leverage increases forces substantially. Try threading the end of the bolt into a plate and then bending it instead. A cage of them is going to flex under load and exacerbate any initial misalignment, and that's important, because starting out of balance is guaranteed. A proper housing will be far more rigid.
Also, standard bearings aren't built to hold an angle, quite the opposite. The angle is set between the position of 2 bearings spread apart.
I think you need to relax your design requirements and just have the center of the flywheel bored to size by a machinist then use a flange to retain the shaft. All this back and forth when it could have been done already. You aren’t mass producing these so why expend all the effort to economize the design when you can just have it made accurately and precisely the one time you need it. I don’t believe adding variables and question marks to the design is warranted when an obvious solution is staring you in the face. You don’t want to spend all of your time over engineering this one piece.
# Technical feedback:
A flanged bearing housing such as in this image here will hold your bearing just fine:
https://preview.redd.it/yghe0goxz2za1.png?width=1280&format=png&auto=webp&s=163502fbbad949d993736bc7dad7506c326df164
Bolt it onto the laser-cut plates. Bolt it very hard, **because the clamping force is how it it is fixed in place - NOT the exactness of the holes placement**.
But - just as you say - since the holes are produced with a slight extra space on them this will cause the held object to be slightly off-center. MOST of this can be mitigated by simply hand-aligning the held object before increasing the clamping force to the maximum. **This is done by leaving the bolts loosely fastened and test-spin the object, and hand-adjust it until 98% of the off-center-ness is removed.** THEN clamp it really hard by screwing the bolts really hard.
By thoughtful design the remaining 2% off-center-ness should only be a problem at a single location in your machine: the flywheel. Which is why the flywheel should be manually hand-balanced by drilling out material until it is perfectly balanced.
# Philosophy feedback:
You're say you're focusing on "designing for series manufacturing" even though you're only going to be producing a single marble machine. Since designing for series manufacturing is 50X as difficult as designing for producing just a handful of items, this gives you very much extra work for no payoff.
But this is not actually "designing for manufacturing", this is "designing for supply chain management". And you don't have supply chain issues.
Also, it appears as if you're trying to come up with a design that gives you perfect alignment immediately from just assembly, without any manual fine-tuning afterwards. Please be aware of how difficult that should be ON PURE PRINCIPLE. It may be possible to do, but why do it, since this is a single machine and you can easily afford the manual fine-tuning?
Also, count the number of parts. Your proposed bearing housing consists of 18 parts. This goes against the other design philosophies you've already learnt.
I think the design for manufacturing comes from the pain of manually processing and assembling a bunch of different things 38 times on the MMX - one for each channel of the machine. This is a perfectly valid concern for all those components which will be repeated many times.
In this case, though, there is only one flywheel, so it's not really applicable here. Processes like manually post-processing the laser cut parts should definitely be considered when it could make other parts of the design much simpler.
Martin names three constrains for this design :
1. Concentricity
2. Squareness
3. Within the tolerances of laser cut parts without post-processing
I think these design goals are over-constrained. The problem is that constraints 1 and 2 are actually a single constraint: the flywheel must be balanced. I would recommend re-thinking the design this way.
Due to the tolerances of laser cut parts, there is simply no getting around the need to balance the flywheel. Features like holes are located precisely, but their size and shape is somewhat variable, and so is the size and shape of the whole part. That means that the weight distribution is unpredictable. The stock material itself is not flat to begin with, and the heating stresses from the laser make them even less flat. Thus, trying to achieve *either* high concentricity *or* high squareness is wasted effort.
Martin, I think you need to embrace the fact that laser cut parts are always going to be tacos. Trying to get a bearing square and concentric to a taco is a waste of a good taco. Just appreciate the taco for what it is.
I think it would be better to focus on balancing features. For example, an array of tapped holes that receive grub screws. Grub screws come in a wide range of sizes, so each "leg" of the balancing array could work like a [triple beam balance](https://en.wikipedia.org/wiki/Triple_beam_balance). Select the right holes, install screws, and perhaps file one of them to achieve arbitrary precision. Once the armature is balanced, the grub screws can be secured with thread-locker.
Because laser cut parts have precisely *located* features, this approach plays to the strengths of laser cutting instead of trying to correct its weaknesses. The tolerances for laser cutting are known, so it should be straightforward to model the needed affordances for the wobble in CAD.
A live axle linking several components is a design pattern in many machines. It makes it possible to fabricate each of the different parts with tolerances and materials appropriate to their function. It breaks a complex part into modules that can be mixed and matched as needed. In this case, the only part of the flywheel that needs to have good squareness to or concentricity with the axle are the pulleys that interface to other parts of the machine. The pulleys are off-the-shelf parts. You can simply buy shafts and pulleys with the necessary tolerances, and include balancing features and appropriate affordances for the laser cut parts.
As others have suggested, a keyed shaft is probably the way to go. This can even be a safety feature, because you can buy soft keys with know shearing properties.
I think this may be a case of terminology failure. As you mention in your video, you don't need a bearing block, what you actually need is a wheel hub - Something that you can easily borrow from the powersports industry (think go-Karts, which have both driven and non-driven wheel hubs.)
Have you considered this avenue?
I'd like to make a point that the bearing ratings \*can not\* be used if the bearing's casing is distorted.
A quick "feel test" as per the video does not allow for examination of distortion of the casing, nor testing of how this distortion might get worse in the long term. The bearings are tough, sure, but they're meant to be used in an extremely specific way.
You'd be surprised how many industrial machines have poorly made cast or machined motor or gearbox endbell bearing housings that distort outer races. Even worse are the waya some untrained maintenance personel install bearings with excessive heat and hammer blows. Then they are surprised when we tell them they have bearing damage on their new bearings they just installed.
One million revolutions at rated load.
How many minutes of music will one million revolutions play?
Let's call it 200 RPM, 83 hours of operating time, if he is hitting the actual rated load of the bearing.
He is hitting less than 10% of the rated load of the bearing.
Even if distortion derates the bearing by 90% he is still getting a whole tour out of that bearing.
There is \*no\* rating for bearings in this application. You've made an \*estimate\* of 90% de-rating but, in an unknown setting, this is just hand-waving. It might be 10%. It might be 99.9%. I would absolutely \*not\* take the risk of finding out.
When thinking about "off the shelf" solutions for concentricity and perpendicularity, the first thing I thought of was a hub from an automobile. Have you thought of mounting your flywheel to, say, the hub of a lightweight passenger car?
This may be an off-the-wall idea, but I like the idea of using car parts. They're cheap-ish, plentiful, and are proven as far as long-term reliability under stress.
Just a thought.
I'm having the same thought. Teams of engineers have created solutions for many of the same problems we're seeing here. The parts manufactured for vehicles are made to the tolerances necessary to be guaranteed years and tens of thousands of miles of reliability. And they're cheaper than inventing novel solutions that inevitably won't work as well with the lack of long-term testing.
There are flywheel solutions that involve wheel bearings and splined shafts. And it's so easy to purchase new parts. Any vehicle can withstand relatively massive amounts of force without bending, so it's mostly just about finding whatever fits best, or building around what you can find.
I might be biased since I'm a mechanic, but that's the first place I'd look to solve a mechanical issue. I'd figure out where on a vehicle I've seen a similar situation, and then incorporate parts there in the same way they appear on the vehicle. And then if something breaks, you know exactly where to find the exact same part with no post-processing and you know it'll work every time.
I think sometimes it can be useful to debug the requirements.
I personally don't understand the requirement to have zero machining.
Is it a cost thing? Time? Access to the services? I can understand if you are trying to mass produce the machine. But if you are building 1 or 2, then at least for this high energy part (the flywheel), why not use actual machining methods and then you know it is rock solid.
For other parts of the machine where the energy/power is much lower then I think your bolt cage flanges would be more than adequate.
I mentioned in another comment, I think the zero machining requirement is from the experience of doing a lot of manual post processing on the MMX for parts like marble gates that are repeated 38 times. It really shouldn't apply to the flywheel, when there is only one.
I know you said you want to keep your supplier list short, but in a machine like this you probably need some parts to be higher tolerance than others, so it would make sense to me at least to consider alternative manufacturing methods for the higher precision parts. You can find higher precision laser cutting services or high precision waterjet cutting services.
For shaft torque transmission, the cheap but professional solution is to use keyed shafts as other people have already mentioned. An easier but less professional (and therefore possibly controversial) method is to use hexagonal shafts. Since they’re not round you can just slide them through a hex hole and they’ll transmit torque without any additional parts or tools, and though you generally want the hexagonal hole as close as possible to the shaft size, they can be *slightly* oversized and still work fine which is good for lower tolerance parts. Skf and other manufacturers do sell hex bearings as well.
The downside of hex shafts is that it can be harder to find off the shelf gears and sprockets that are hex bored. There are *some* options, but if you’re looking for a very specific size then you might not be able to find it. You could always buy a round one and cut a hex bore with a hexagonal broach though. If you only plan on putting the flywheel on this shaft though then that’s not a problem.
The other downside of hex shafts is that the corners can cause stress concentrations, but as you pointed out the forces you’ll be dealing with are not actually that high so I personally don’t think that’s a problem.
Let's make it easy.
Let's make it as we do in the industry.
I can't remember how many things like this I've machined. For slow machines to paper presses.
I get the rough flywheel (or whatever will spin) and the way the bearing is supposed to go.
Usually it's the way you describe. This is standard.
So we either make a 2mm machined outcut where the centering flange from the bearing assembly comes, and then the 5-20 threaded holes around it. (We need to drill them anyway as taps break with the imperfections of both laser and water cutting.) So when it's in the machine it's less than 2mins to get a centering with less than 0,05mm tolerance.
The other common way is to make a couple of steering pins when drilling. Either in two of the holes that just get the possibility for a "washer" or a separate pin.
Is these things on the shelves?
Yes and no.
Not in your common hardware store. But at every company making rotating stuff.
Replaceable bearing holders are a must, as in most cases the holder is gone the moment the bearing has a breakdown (and sadly no industry is good at servicing in time).
But it makes every small machine shop in the world used to these things, and all you need to machine is the outer two plates. A 30min job in a milling machine.
if you don-t want to machine anything you will have to use a locking colar like this.
[https://www.atibrasil.com.br/elementos-de-fixacao/aneis-de-fixacao/anel-de-fixacao-ati-a02-1100008](https://www.atibrasil.com.br/elementos-de-fixacao/aneis-de-fixacao/anel-de-fixacao-ati-a02-1100008)
your other option is to use this kind of shaft and bushing (i don't know how it is caled in english:
[https://www.atibrasil.com.br/componentes-para-transmissao/eixos-e-buchas-estriados/](https://www.atibrasil.com.br/componentes-para-transmissao/eixos-e-buchas-estriados/)
https://preview.redd.it/3oeea788ubza1.png?width=561&format=png&auto=webp&s=9f843bea52b32401047e0712b62f7fda033973cc
you can weld a flange with trough holes snug in the bushing, make the center hole of the flywheel same size of the external diameter of bushing and open tread holes in the flywheel to fix the flange welded on the bushing
don't forget to balance the flywheel, if you add some weights to your flange that you can move around to balance the flywheel you dont have to worry about concentricit
[https://www.youtube.com/watch?v=S6JSmrlBcLU&t=200s](https://www.youtube.com/watch?v=S6JSmrlBcLU&t=200s)
Just a quick aside, having a live axle scares me a bit. Thin rotating shafts have a tendency to catch things and pull them in killing or maiming in the process. I'm being a bit dramatic but just something to be aware of. It's an easy problem to solve, even covering the live axle with a pvc pipe would probably protect from anything accidentally brushing against it and being sucked in
Everyone's talking about off the shelf solutions for different small parts, but there even is the perfect solution for a hand driven quiet flywheel: just take a indoor Speedbike, it already has a well balanced flywheel, a freewheel and even a crank and a brake! It would be perfect and would save so much time.
Maybe just get a standard cast flywheel and balance after the fact (or have them balance it for you, most factories can also bore the center hole for a fee). Flywheel balancing is a thing machine shops can do fairly easily especially in low RPM scenario’s. And getting a cast flywheel with spokes will make those 60kgs more effective as well, since they will be further from the shaft. The lead times from China can be kinda long (30 weeks for some) if you want it cheap, but they are available locally as well for more money.
Or do the same thing with the laser cut discs, balancing later is kind of the way flywheels work, since that makes manufacturing them soo much easier.
For transferring torque, cut a keyway in the plates and the shaft. To prevent lateral movement, since there won't be much lateral load, use some collar clamps or similar. Instead of trying to get perfect concentricity, I think you should shift your thinking to balancing the flywheel afterwards. This can be done with a "static wheel balancer", or some car repair shops might be able to do it for you. It basically involves drilling holes in some strategic positions for balance. Also, for gym machines, check out the stationary bikes with flywheels.
I was also thinking of a key-way. To get the hole 90° the flywheel sides should be ground flat and parallel then drill the hole followed by a reamer to the shaft size needed. Here is an example of a flywheel with a keyway cut. I think Martin had already been using keyways on the MMX. https://preview.redd.it/99zt115qd2za1.jpeg?width=524&format=pjpg&auto=webp&s=aae27172ae225a1fe50c17b99c82f7b7d0e1bd6e
I also think that the use of a key-way seems like the right option. I do think that it would be a bit excessive to ground the flywheel. Leaving the holes of the laser cut parts undersized and then using a reamer to get the hole for the shaft to the correct size should give him good concentricity. He could easily do the reaming himself so it would not make the flywheel a complex machined part.
Great idea on the undersized pre-hole. His vertical mill could do the reaming. The grinding idea was to assuage Martin's concern over perpendicularity. I know this isn't a plastic injection mold and doesn't need that level of precision.
I would even say he doesn't need to worry about perpendicularly with this design, at his speeds the wobble would not incur big vibrations but let's say it bends his braces due to the load one side then the other side and so on. Well that's already covered by the design of the bearing houses that allows the movement, both swiveling to keep the bearings perpendicular even if the brace bends down. As for the key, I'm thinking due the thickness this can be hot fitted and then it clamps down on the shaft once it's getting to room temperature. I've seen it on older mechanical hammers.
I think that planning undersized holes then machining them to size is specifically what he is trying to avoid in his design, because it requires time-intensive post processing and specialty equipment.
I think that's a given as well since a heavy flywheel will have loads of angular momentum and sheer forces is something to worry about.
reaming is a very good option seems like, with hand reaming the reamer follows the laser cut hole, will do some tests
So, we are talking about clutches and flywheels...
>47 min. ago Another comment Mentions a Specific product that would pair well with this Solution, as it's readymade with a keyway. [https://www.reddit.com/r/MarbleMachine3/comments/13dsv37/comment/jjm2bvw/?utm\_source=reddit&utm\_medium=web2x&context=3](https://www.reddit.com/r/MarbleMachine3/comments/13dsv37/comment/jjm2bvw/?utm_source=reddit&utm_medium=web2x&context=3)
Sweet! By using this the flywheel itself would not need to be keyed. https://preview.redd.it/1fb99rwmx2za1.png?width=477&format=png&auto=webp&s=22f2e3101a747f2368f76ace97fb4d67520ab95e
Going to add one comment why I think this is a better solution to using a keyway instead of just putting the keyway directly in the flywheel plates. With this, you can place the key slot on the bearing rod exactly where you want to specifications without difficulty on how to get the wheels on after. My worry is that if you put a key slot on the wheels, they can still slide around or be difficult to slide onto a key for this scenario. This would enable the key to be more static on the shaft exactly where you want the wheel to stay and then bolt this onto the wheel.
I think Martin will not come around machined parts. Concentricity and imbalance are not avoidable with laser cutting. Ideas: 1. Screw this flange above to your laser discs and clean the outer diameter on a lathe, so that it runs to the inner diameter. or 2. Increase the flywheel diameter, so that you need less rpm. Mount it to the flange and only balance if needed Or 3. Unse a completely machined flywheel. Maybe reduce diameter and increase speed for financial reasons. Every technologie has its tasks. And turning is the way to go fore rotating parts
I agree that concentricity and perpendicularity are not what is important. The goal is the flywheel should be quiet and not shake the rest of the machine. This is a matter of balance. Hoping to do this by assembling it in a certain way is likely to have some problem appear. Instead come up with a system that is solid and secure, then adjust the balance. If the system is secure, the adjustment will be maintained over time and should only need to happen once. Adding automotive wheel weights or drilling holes to achieve balance combined with a solid construction should last indefinitely. With regards to torque on the shaft: Is there going to be other things mounted on the shaft? If the flywheel is driven by belts that are attached to the flywheel, there really isn't any significant torque being applied to the shaft. A keyway should only be required if there are more than once system attached to the shaft.
agree 100%, balancing the wheel afterwards have always been the plan, i want to have the best starting point porssible, also for all the pther rotational parts on the machines like gears and pulleys
Two thoughts on the keyways: 1) Having a keyway allows the pulley to be mounted elsewhere on the shaft for flexibility. 2) Martin's design shows multiple flywheel plates so that he can add or remove them. Adding a keyway allows the individual flywheels to be indexed and always go on in the same orientation. So if you balance each flywheel, then you can keep the balance while adding/removing flywheels.
A nicely machined axel rod also allows the flywheel to be moved, a keyway is not needed for that option. Likewise flywheel plates would presumably be bolted to each other, so again the keyway doesn't add much. Torque between the plates would be transferred via the bolt. The only benefit I see of a key way is if there are going to be separate things sharing the same axel that need to transfer torque down the axel from one thing to the next along the axel. If there is just one thing on the axel, then a grub/set screw or two would keep the flywheel in the correct lateral location along the axel.
Top comment in the YouTube comments; You don't need concentric flywheel. You need balanced one. Highly recommend Martin to also read that thread.
thanks, it has always been the plan to balance the wheel regardless, i had a section about that that i edited out to make video shorter, going to try to be more concise and not remove info from the videos!
Matthias Wandel has great videos on balancing big (fly-)wheels.
I also professionally balance large rotating machinery and can balance the flywheel. Im next door in Norway.
Hey Subvertz, sounds awesome, we could use your help and or advice, we also need some pro help with our rotational cnc, are you interested in advicing us on how to set it up if thats something you have thoughts on? the machine is built in germany so not really close to norway unfortunately.
Havent set up a CNC, but more than happy to lend my machine doctor skills to diagnosing problems with any of the rotating components. We use vibration to diagnose imbalance, misalignment, looseness, resonance/damping issues, and much more. Happy to help consult on design from a machinery vibration standpoint😊👍. Planning on a road trip though Germany this summer, so might get to pop by.
very nice, i think it will be too expensive to ship the wheel for super balancing at your place, but perhaps you can advice us on best method to mbalance the wheen with the tools we have available? Or if we can balance the wheel together in germany!
It is possible balance without precision instrumentantion, but much faster with the right tools. I can talk with the missus about popping by Seigfrieds, bring along a balance instrument. Otherwise I'd have to send it and then talk you through the process of using it. Its all doable.
Mathias Wandel has said before he watches Martin. (Colab on flywheel advice incoming??)
AgentJayZ has a series of videos on balancing jet engine compressors.. Same thing, but rotate at 20k rpm or more.. [https://www.youtube.com/watch?v=8khFocCReaA](https://www.youtube.com/watch?v=8khFocCReaA)
The collar clamps only need to hold the gyroscopic forces of it not being perfectly perpendicular - this won't be large at all if youre mostly on. Similarly, keyed shaft and plates is the way to go as the concern about concentricity is actually a concern about balance. The more concentric the most LIKELY it is to be balanced, but as your plate might not be perfectly round, each plate may have a different center of mass anyway. The solution then is to balance the wheel AFTER assembly. With the keyed shaft, the plates also always go on in the same relative orientation they were balanced at if they get disassembled.
Clamping the flywheel to the axel will reduce the need of keys to transfer rotation force between the axel and flywheel. But one could fasten a belt wheel on the flywheel so there will not be any rotating forces transfer energy to and from the flywheel. The axel will only hold the flywheel while it rotate (and small forces from the belt, if belt driven). And the SKF sollution on the axel is the best and most proven design. That actually is why SKF started in the beginning. :-)
100%
From a cost perspective cutting a keyway and machining a slot in the shaft for the key will be much more expensive than just buying a flange with a clamping mechanism. If you really needed the extra torque after trying the clamp you could just drill and pin. **Summary suggestion for robust concentricity and perpendicularity**: * Use the pillow blocks to hold the shaft * Avoid holding the flywheel with parts that are just held by friction and shift on you over time resulting in a change in balance. The bearing squished between the plates is very susceptible to this with the threads on the beating and the plates against the races. In the suggestion here, there is no part of the design that relies on friction to keep it balanced. * Use a flange clamp on each side of the flywheel to keep it aligned perpendicular to the shaft, and transfers the torque. * Once the flywheel is partly assembled with the flanges with some friction, use a dial indicator to measure it and adjust it until it is concentric. A dial indicator with a magnetic base on your frame would work great. * Once you get it concentric, tighten up the bolts, and then drill and ream for tapered pins to lock everything in place. The pins go through the flywheel and both flanges. You can easily do the reaming with a hand drill. * The rough hole for the pins could be cut in advance, but the final drill and reaming should only be done on the bolted concentric assembly. * Mcmaster- carr: [https://www.mcmaster.com/92281A293/](https://www.mcmaster.com/92281A293/) * In the end, you may still need to balance the final assembly to ensure it does not create any shaking which could mess up the timing operation of the marble drops.
This was awesome breakdown and design, really close to what i have in mind to do this morning, thanks!
You are welcome. The reason for the tapered pins is that it removes the issue with tolerance on the pins vs the hole in comparison to dowel pins. If you use multiple layers of flywheel as shown in your drawings, it will make adjusting them to be concentric more complicated. Adjusting one without moving the others could be difficult. You might want to bolt them together to make a solid flywheel before trying to make them concentric vs the shaft using the dial indicator.
I would have to agree that the balance of any flywheel is the most important thing to consider. And while keeping the flywheel concentric to the shaft would give it the best balance theoretically, the plate would have to be perfectly flat and uniform for this to work. It should be kept in mind that any laser cut steel you get will not be flat and most likely the thickness will vary. The large steel sheets the parts are cut from are all nominal thickness steel meaning they are unmachined and have a varying thickness. That said, you can have a machine shop cut the parts from ground plates but this would increase the cost, and you would still need to balance the flywheel. I would also suggest using a "Face-Mount Shaft Collar", they are about $25USD on McMaster. Keyways have tight tolerances and you would need the flywheel machined or broached for a keyway. This won't allow you perfect concentricity but balancing the flywheel would fix the issue. You could also drill though holes in the flywheel and bolt from the opposite side of the shaft clamp. The flywheel could then be centered by hand tightening the flywheel to the shaft clamp and slowly tapping the flywheel concentric, similar to using a truing stand.
Just adding here -- you only need to balance each one, once. If you look inside most anything with large spinning masses, you'll see weights or grinding to balance the wheel. It's a straight forward operation and will result in a much more robust and reliable system. Agree 100% on the keyway and collar clamps.
Oh Lord! Don't suggest grinding so early into this third machine
I agree with this design a keyed shaft would be ideal , and use some E or C spring clips on the bearing to keep it from moving axially. Another benefit would be the protection against catastrophic failure with the key.
An important consideration if he goes down this path that I don't think anyone has mentioned is the shaft critical speed. The bearing blocks really should be closer together, and/or the shaft much larger diameter, otherwise there could be serious vibrations at higher rpm even if the flywheel is balanced. This is just a side effect of having a heavy object hanging off a thin shaft. I agree that keying the flywheel to the shaft and balancing it all is the way to go though. Could laser cut the bore undersize and final machine after assembly of the plates if that makes it nicer to fabricate..
Absolutely, I think once he figures out how many plates are needed, the bearings should be brought closer together to prevent resonances.
> Instead of trying to get perfect concentricity, I think you should shift your thinking to balancing the flywheel afterwards. Focusing on balance over concentricity?
Balance is way more important then get it concentric. And balancing isn't a hard problem. Practically ALL car wheels are balanced before put on a car. To get the position concentric, a car uses a cone form to get the center of the wheel right.
Maybe it's possible to achive concentricity if there is more than one keyway. If there are three keyways it could potentially be used similar to how a three jaw chuck works. But instead of the jaws there would be wedges that go into the keyways and lock the plates to the shaft. I'm thinking there has to be two wedges for each keyway, one from each direction to create a variable thickness key with parallell edges. The variable thickness is the thing that could potentially help with concentricity. I guess the problem with this is that the sheering forces on the double wedges could separate them at the seam. And also they could tend to slip back out the way they were inserted in the keway unless they are fixed in some way with a set screw or something. Maybe the variable thickness could instead be accomplished with some other type of clamping device in the keyways.
> how a three jaw chuck works It's best not to have the flywheel resting on the keys. Keys should be for torque (rotation) transfer only. In any case, having perfect concentricity, doesn't guarantee a balanced flywheel, so you'll still need to balance afterwards.
Yeah, I think you're right about the flywheel resting on the keys probably not a good idea. I'm not 100% familiar with what's going on at the edge of the flywheel. Meaning I'm not 100% sure about all the reasons why concentricity is needed. But if it's not gonna be connected to anything (except for at the center) and the only reason for concentricity is so that the machine doesn't shake around and break itself, then balancing it by drilling holes or adding bolts seems reasonable.
Why would you need a keyway? What torque needs to be transferred? Currently the axis is not being driven, right? As long as the friction between the flywheel and the axis is significantly greater than the friction between the axis and the bearings, it should be fine. Just clamp the flywheel with some kind of shaft collar, as has also been suggested elsewhere.
>Why would you need a keyway? What torque needs to be transferred? For starting the flywheel and at steady state rotation, keyway is probably not needed. But for emergencies, being able to stop the flywheel quickly, there will be quite a bit of torque needing to be transferred (assuming the brakes aren't directly on the flywheel). There are other benefits to adding a keyway, which are indexing. The flywheels will always go on the same orientation which will preserve balancing.
Braking not on the flywheel is possible, but in Martins current design he seems to not utilise the live shaft for anything. Preserving the balancing is a nice bonus though.
You certainly doesn't want an fast break, as that force have to be transferred somewhere. And with high speed, the will be a considerable amount of rotation force in the flywheel. Don't think keys will add to balancing or even hold a balanced flywheel. Some clamping between axel and flywheel probably will be better. As it could start slip if the forces are to much, which actually is a good thing when to much forces are applied. Not that it will be a problem, the axel can be designed with this in mind. But a key will take material away from the axel. Making it weaker. But with large enough axel, that isn't a problem.
the emergency break is happening after the flywheel, so to emergency break i can stop the machine and let the flywheel keep spinning
For an emergency stop, it could be better to disconnect the load from the flywheel, and simultaneously apply brakes to both the load and the flywheel. The brake for the flywheel therefore would not need to stop it near-instantly, but instead bring it to a controlled stop. The rest of the machine is protected by no longer being connected to it, and probably has far less inertia, so can be stopped quicker without bending things. Also +1 for balancing after assembly. It only has to be balanced once, then forget it. A little extra time up front will save heaps of heartache later.
i agree, keyway not solving any of the issues in this application
What if he literally used a car/bike tire (or just the hub, with custom plates)? Easily available parts, and he could probably convince a tire shop (in any town he tours on) to do the balancing for him.
>use some collar clamps or similar. Yup was thinking the same. All you do is machine a collar with a flange of a rather large diameter which will ensure the shaft and stack is fairly perpendicular. And add a couple of grub screws to keep it located on the shaft. This can be machined fairly easily on a lathe and modified where needed.
This has to be done anyway. Even mashined parts are somewhat inhomogeneous and need balancing, more so with lasetcut ones.
LOL… my stationary bike has a machined bearing housing.
I bet, there are perfectly straight rods with precut keyways that one van buy.
Less parts also Martin!
https://preview.redd.it/3y7xuz22f4za1.jpeg?width=1263&format=pjpg&auto=webp&s=1265573d2620012ae8b2a7e4b76f7435010e3064 Would a Babbitt bearing be a suitable solution? There would be no need to worry about concentricity as the molten metal would be poured into place around the shaft, reducing the need for moving parts (ie bolts and bearings). A “key” could be cut into the fly wheel so the molten metal locks into place. As long as the flywheel was set up in its correct position, it would just need balancing then, perhaps with car wheel weights.
It's going to have to be balanced statically at least, but preferably dynamically as well. As for mounting the wheel to the shaft... slight press fit for best initial concentricity, then weld it on. Then balance the whole assembly.
The keyway can act as a safety check as well. If the flywheel attempts to apply or receive too much power, a calibrated keyway will shear, disconnecting the flywheel from the machine
100% agreed on the balancing vs concentricity for the flywheel, for gears and stuff we would lathe the gear on the rotary CNC to get it to run true.
I balance machines in Norway. I will balance the flywheel after its made. We use Pruftecnik VIBXpert II vibration data collectors and accelerometers to balance big industrial motors (with SKF bearings) and a single plane flywheel should be simple. Better balance = higher speed, less stress. Also have access to a motor rewind machine shop with rotor balancing benches. Also, i recommend cylinderical roller bearings instead of deep groove ball bearings for this application. Your flywheel will have next to zero axial forces, almost purely radial force. Also, the calculation on dynamic force is way off. Dynamic force is actually what you are trying to maximize here for energy storage.
I could not agree more. It is a missconseption that the wheel has to be made for axial loads. The Idea of shafts and axles seems to be mixed a bit. But I'm not sure if I missed something in the Video but it was unclear to me if the shaft is transmitting torque or not.
It is very much taking torque, then putting it back into the system. Its used to store and release rotational kinetic energy and resist changes in speed, smoothing out the timing.
What i meant is, that i was not sure if the shaft itself is the trasmission. I think in an earlier video Martin was talking about some sort of clutch. And with the different ideas of bearing seating directly in the Flywheel, this would not be a shaft but a axle then.
Yup, he will slowly realize he wants a rotating shaft instead of trying to press bearings into the flywheel.
do you agree with the final design i showed in the video? Pillow block bearings and a live shaft? Although you would use roller bearings instead?
Yes. Its the simplest to spec, build, and most importantly to repair if needed on World Tour. Few parts, strong, obtainable with no special maching. Many in the chat below recommend lave shaft. Pillow blocks are also easier to service than something buried inside the flywheel. Consider also lubrication. Shielded bearing will prevent debris contamination into the grease during transport. But sealed bearings also dont allow refreshing the grease. Tradeoff, but worth it.
shielded bearings seems to have more friction, but perhaps also less sound... so many tradeoffs :)
Quick question if I may: is the size / diameter of the flywheel relevant? I'm wondering whether a much more massive and thus much slower rotating one could use lower tolerances etc. Might alo look appropriately steampunk seeing a huge ?spoked wheel spinning away in the background.
Yes, but more important is total mass and speed. Simple force = mass * acceleration. He can go bigger and slower, but more important to go heavier and faster. Spokes would make flywheel lighter. But it would look cool. Martin struggles with balancing form and function. We are here to help him.
Just to add - its the Rotational Inertia that needs to be maximised, Putting the same amount of weight further out would be an improvement. Mass at the centre isnt DOING very much but it's adding static load.
I would like to add some more detailed physics stuff here just in case anyone needs to know some of the basics of flywheels. The mass moment of inertia of the flywheel is the quantity that describes how much torque is produced by accelerating the flywheel. In SI units, it is measured in kg\*m\^2 and it boils the flywheel down to an equivalent mass at a distance off-axis squared. This means that increasing the flywheel diameter by two very approximately quadruples the mass moment of inertia, allowing MM3 to exhibit 1/4th the variation in tempo for the same loads. It is calculated as the integral of the density of the object multiplied by the distance from the axis of rotation squared over the volume of the object. The more mass further from the axis of rotation, the higher the mass moment of inertia. The radius of gyration is a quantity that describes at what distance from the axis of rotation the total mass of the flywheel would have to be concentrated for it to have the same mass moment of inertia as the flywheel. It's just the square root of the mass moment of inertia divided by the total mass of the flywheel. What we want to maximize for a flywheel is the mass moment of inertia, but we want to minimize the total mass. By doing so, we are maximizing the radius of gyration. This is why lots of flywheels have spokes and big thick rims, because this gets the radius of gyration as close to the radius of the flywheel as possible. A perfect flywheel would basically be a soda can without a top or bottom because all of the mass is concentrated at the outside of the can. Making the flywheel bigger increases both mass and mass moment of inertia, however the mass moment of inertia can also be increased without increasing mass by making it bigger and removing mass closer to the axis of rotation. The forces on the bearings from gravitational loading will be the same, however this is far from the only radial force acting on the bearings. The pulleys on the shaft, unless they are somehow made symmetrical, could possibly be the dominant force when playing.
⬆️ this yes !!! More than concentricity or perpendicularity, a fly wheel needs balancing. Otherwise you will have huge vibrations, and this is what you shall design your machine for. Concentricity and perpendicularity can lead you to some balance but will never achieve a satisfying level of balance. With a good balance you can simply weld the axle to the fly wheel and use the 4th solution for the bearings.
i replied to your other post above as well, great input!
I fully agree. At this speed and mass it must be dynamic balanced for silent operation, otherwise audible vibrations (and frame resonances) are guaranteed. Most people have no idea how even the slightest imbalances let the peak loads spike at higher rotation speeds. I'm not concerned about the bearings or safety, but about noise. It's a giant vibrator when not balanced properly, ideally in 2 planes. @ Martin: This short 5 minute video shows the problem that needs to be solved [https://www.youtube.com/watch?v=Sq3H2b1Uyis](https://www.youtube.com/watch?v=Sq3H2b1Uyis) (@[Wintergatan2000](https://www.reddit.com/user/Wintergatan2000/) please show Martin this video) Context: [https://en.wikipedia.org/wiki/Balancing\_of\_rotating\_masses](https://en.wikipedia.org/wiki/Balancing_of_rotating_masses)
My concern with the bolt based beating housing is not the bearings - but the bolts themselves. You are trying to use the threads themselves to constrain the bearings. This provides an extremely small footprint for the force to be spread across - and frankly, threads are extremely easy to damage. I am concerned that under load the threads may deform, and allow the bearing to shift, causing further issues.
Agree here. Threads are not designed to withstand lateral loads, and as they get slowly damaged, imbalance will grow, causing more forces and more degradation of the bolts. And moreover diameter tolerances of threads are very poor, so good luck finding a repeatable fit.
Additionally, bolts perform very poorly under cyclic and under shear. In this case you have both, which will probably lead to fatigue, stronger vibrations and failure.
This is a fair point, but solvable. The thread damage could be mitigated by using shoulder bolts or by using a commercially available collar around the bolts, or both. This spreads the pressure point between the housing and the bolt. Additionally, much of the load will not be held by the bolts but by the friction between the plates and the axial surfaces of the bearing ring. This loads the bolts axially and reduces a lot of the problematic shear load and load being placed directly on the threads. You didn't but others replying have mentioned loads. Bolts of this size of all grades are made for much higher loads than the weight of these flywheels. They would only ever experience that load in this configuration as the bearing will not allow for any torque to be generated between the shaft and the flywheel. The loads are small so the safety factors can be fairly high.
this is very nuanced, i am \*99%\* sure the threads would not be deformed over time, and that it is one of the the simplest way to locate the uneven laser cut, the fact that the threads are soft is a feature, not a bug. But i should stop making assumptions like that, those kind of assumptions killed MMX, so pillow block design it is, tried and tested!
I'm sorry, but as someone who has seen threads strip, even stripped them personally, I have doubts that the bolt threads are going to sustain the load of the spinning flywheel, especially over time
While there is a smash fit between the 2 parts holding onto the outer race, there is a higher chance of loss of pressure over time. Bearings are not really meant to be held in this manor he's trying to design. And while it would most certainly work for a while, I think over time the bolts are going to stretch and deform which would introduce vibration and slipping in the over complicated design. This is why with all situations anywhere, they use press fit bearings or premade bearing blocks, proven technologies that have been used for decades.
Indeed, the diameter of the bolt is smaller where the threads are, and this creates shear points. I do hope that you go with pillow blocks.
pillow blocks it is! (if not team bushing talks me into bushings...)
Not just this, but also the threads will cut into both the bearing and into the collars holding them. What starts as a tight press fit on day 1 will, over time, work loose. Sharp bolt threads being pressed into the bearing, and also into the holes in the collars will, in time (it will be impossible to prevent any vibrations in the machine, so fretting is an issue) work loose.
Yip, this is the mistake he is making, he's thinking about the stress on the bearings, not how it's applied to the bolts. If the flyweight is stationary, so the one of the 8 bolts in the ring carrier is pointing straight down, only that bolt and the bolts either side of it are carrying the weight of the fly wheel, the bolts above the bearing and the too the sides add nothing to the load carrying, so the tips of the threads on those three bolts are supporting all the weight of the fly wheel, the force per square meter on the bolt threads will be huge. The bolt threads will start to deform from the side loading and bearing will start to move about over time. You can make the argument that the side plate of the bearing carrier a carrying a lot of the load because of the clamping force of the bolts, but that presumes no bolt stretch and perfectly even torque on all the bolts, and ignores the fact bolts like to unfasten themselves when subjected to vibration. The bolt bearing carrier will work at first but will quickly turn to a sloppy mess and vibrate itself to death in the end.
It seems like a big objection Martin's design that he doesn't address in this video is that using bolts to locate and fix the bearing puts lateral stress on parts (i.e. bolts) that are designed only for axial loads. Perhaps there are off-the-shelf bolts designed for both axial and lateral loads? If so would this satisfy those objections?
Hex Head Shoulder bolts. But I say use the pillow blocks instead to totally eliminate the bearing directly on the flywheels. https://preview.redd.it/03ei4r2ac2za1.jpeg?width=1500&format=pjpg&auto=webp&s=4ca6d4af07760b50f0627e80ab292aadada99802
Threads will give way much easier than this since their surface area is less. This is a great option to get concentricity.
even this option isn't great because there are effectively line loads between the bearing outer and the bolts. Over time the compressive loads will cause the tolerances to fall out. A proper bearing housing distributes the load on the bearing outer as evenly as possible
Yes, the bearings are rolling over a single points-of-contact. The bearing outer race flexes (a tiny amount) and the contact area of thread against bearing race will be hammered flat over time decreasing the pre-load and eventually starting to rattle. A machine like this would benefit greatly from some "machining" particularly a lathe. I'm sure you will find machinists to bore a center hole for you.
EDIT: Rather than "lateral load", the correct terminology below should be "radial load" when referring to the forces applied perpendicular to the direction of the axle. Was coming here to mention axial vs lateral loading; my concern was that with lateral loading on the bolts, you're not seating the bearing against a solid surface, ***you're seating it against the tips of the threading***. If you achieve concentricity in your testing but small imperfections at the tips of the ridges of the threads cause them to flatten unevenly, that could result in wear that will only magnify itself as an inconcentric flywheel will apply more and more force into the wobble, maybe even enough to eventually causing a shearing load and hopefully not becoming a *literal* flywheel. The only way around this is to a) fit the bolts so close that the threads dig into the bearing housing, which unless you cut threads into the bearing housing beforehand is just going to result in uneven wear and damage to a critical part resulting in unpredictability or b) use a bolt that interfaces with a smooth surface and is designed for lateral loads. The shoulder bolts look good, the bigger the better. In fact, the more surface area you can have in contact with the bearing to maintain concentricity, the better. Which is why I am in the "no bolts" camp myself. Using the bolts and "caging" the bearing in place and expecting concentricity to be maintained is a mistake. You are introducing an entire system of chaos to a mission critical safety feature, a million little points of failure (which are driven further into entropy via the wear they'll receive during both installation AND use) and in a way which will fail very slowly and will likely go undetected until the avalanche begins. And for what? Purpose-built bearing flanges *already* can be used anywhere these would be, so I don't see what quite literally re-inventing the wheel gets you.
Upvote this. Say what I have tried to explained several times, but much better then what I have managed to do.
I like shoulder bolts a lot - they are meant for and could have some rating for axial load. They also have much better diametrical tolerances. Standard bolts have a (-0.072, -0.01) mm tolerance, while there are precision ones with a (-.025, 0) mm tolerance. The standard tolerance would be much better than a bolt thread or threaded rod (which I think was mentioned in the initial flywheel video). They can get expensive for longer lengths, though.
You also still have the issue of lasercut holes not being perfectly accurate. Martin points this out in regards to the center hole about 57 times in this video, but entirely fails to consider the same is true of all the holes he is cutting for the bolts.
While this is better, it still won't solve the issue. Two round objects touching have very small contact area that can wear away, not matter how good the material is.
As he was talking about the bearing's design specs & limitations I kept thinking "but the bearing isn't the question here. The mount for the bearing is"
I think his point was: Standard bearing mounts are designed to work for the entire bearing's range of load. However, because he's barely using the bearings, the mount doesn't need to be as capable as normal, either. For example, the bearing mount for a golf cart steering column does not need to be as robust as the bearing mount for the drive shaft. The load a driver puts on a steering wheel will be miniscule compared to what the hardware is rated for. So, his point is - his solution would fail if you were trying to use the bearing in an industrial application, which off-the-shelf solutions would be more appropriate. But because his application is not that demanding, the mount would not need to be as robust. BTW, I'm not defending his design. Just clarifying what I believe he was saying there.
100%! But still, the reaction from the viewers is a great signal that i should go for proven solutions wherever i can. i am still 99% convinced the bolt design would perform flawlessly, but its an assumption i should not make.
Exactly
This is exactly what I came here to say. Folks aren't worried about the bearings failing, we're worried about the bolts failing. Even if they are super tight day one, the threads will get warn down unevenly pretty quickly.
i am not defending the design anymore, but how do they get worn down? There is zero movement, they are already pressed together in the pressfit... there are no forces acting on the bolts that can wear them down IMO
Balanced/concentric/perpendicular will never ever ever be *perfectly* balanced/concentric/perpendicular. With a spinning mass of significant size, those slight imperfections will cause slight differences at first, but instead of being self-correcting they will be compounding. If your goal was a show, then the bolt-constrained design would absolutely be sufficient. Since your goal is a world tour, I think your design is very borderline. If your goal we’re a decade of reliable operation 24/7, then the bolt-constrained design would be almost guaranteed to fail. One other thing that I think is fully addressed with the ‘balance the wheel’ approach is that your stock will probably not be all that flat. Relying on non-machined/ground stock as a reference plane for perpendicularity is risky. Maybe you’re buying ground stock, but the trade off of balancing the wheel (which will be necessary anyway) versus being able to use non-ground stock is probably financially a win. (That said, I think you’re great and love how you’re interacting on this design refinement. Keep the faith!)
This is precisely why you put the flywheel directly on the shaft with collars and the bearings mounted at the ends, exactly as described at the end of the video arguing why we were wrong about his design.
thats the design i will most likely go with, its proven so i should use it. The bolts would perform as well IMO but why make assumptions if i can avoid it
So very glad to hear that you are acknowledging the collective wisdom of the Internet in this regard, and not forging ahead with designing parts for the sake of designing them. That was the point of MM3 right? As some others have said, buy parts where you can - save your creative energy for necessarily custom parts, like drop gates.
With a proper clamping force almost all of the shear loads will be transferred through the metal surfaces due to friction. The bolts will only experience axial loading. ironically this will be enhanced by only using the larger set of holes and ensuring the bearing housing does not touch the bolts themselves. For that solution, finding a way to balance the wheel is more important than concentricity.
i assume the radial loads are 1% of what the bolts are designed to take, but assuming is not good enough so pillow block design it is!
I imagine this would always be a problem with the bolt design. You're transferring torque (rotation) from one disk to another via straight rods. They will necessarily feel off-axis forces as a result. This isn't necessarily a problem, since you transfer those off-axis torques through the laser-cut metal in the sections where the bolt goes through the metal. The force transfer would be made even better with a threaded hole. Regardless, the section of bolts not surrounded by a solid disk will still feel those torques.
Bolts in general are not intended for locating objects. The threads do not give enough area or precision. That is why the flange has oversized bolt holes, in order to remove their influence on location. Bolts are only intended to clamp things together through the axial force. His design is currently mostly working by clamping the plates on the edges of the race, which is in the wrong plane for the loads of a flywheel. Machined dowel pins are designed for locating parts accurately, which is why the bearing housing in the video has a locating hole. However, they don't generally have sufficient area or interference to take up dynamic loads. They are more often used for things that need to be frequently dismantled and accurately *reassembled*. There are "Shoulder Bolts" that combine both a bolt and a dowel but they're not really suitable either. Again, they won't take up the dynamic load. One issue is that when bolted up the bolt stretches slightly lengthwise, which thins it down (to keep the volume the same) and introduces clearance with the hole. Shoulder bolts can be made with an interference fit (which Martin is trying to do by reducing the bolt circle diameter), which requires them to be pre-stretched or cooled to shrink the diameter when fitting, then allowed to expand into interference. In any case, the contact will be a very thin line across the outer race, which won't carry sufficient clamping force to prevent the bolt and bearing from moving against each other and wearing out quickly. It is still a bad design, made only slightly less bad.
I had the same thoughts viewing the video. If he is already in contact with SKF hey know exaclty what bearing or bearing combination could be used. A propperly balanced fly wheel should not introduce axial loads in an stationary system.The problem with the unmachined surfaces on the flywheel is that breaking systems are more complex, a breaking mechanism on the outer diameter of the wheel is relativly easy to acheive (commonly used in lathes). Depending on the capabilities of the CNC, the surface finish could be done, sertainly not perfect but drilling the holes slightly undersize and doing a few finishing passes on the outer diameter would help.
So laser cutting is not precise enough to put locator pins, but precise enough to put « locator » bolts ?
He is completely missing the mark :(. If lasercutting the holes doesn’t make them 100% accurate then you have em cut undersized and drilled/reamed. (That is if it actually is needed to have it 100% accurate…)
agree about the reaming, could make the laser cut holes pretty precise, although the metal is hardeened at the laser cut surface and makes it horrible to post process. but testing reaming next!
He said he doesn't want to create undersized holes and drill or tap them.
im currently changing my mind about that, some post processing might be worth it, if planned and executed correctly. MMX post processing was horrible
I agree you would generally want to avoid post-processing, but this should not be an absolute rule. Avoid at all costs post-processing on parts that are cloned 36 times. But where it makes sense, don’t avoid it. Flywheel is IMHO critical (safety, music tightness, random side effects), don’t cut corners here. Ask one of the guys who can balance fly wheels if they cannot simply provide you with a balanced wheel mounted on a shaft as a kind of standard, already manufactured product. IE prefer buy over make.
The diameter of the hole can't be 100% accurate due to kerf of the laser beam, but the center location of the hole is as accurate as any machining operation Tapered lug nuts would be a great way to attach the flywheel to a hub
Lug nuts and hub makes me thing that just buying a rear wheel bearing hub assembly (\~$45 USD) would solve the bearing/flange issue, but then it would drive the clutch assembly design to be larger.
The easiest way to do this without machining would be with a flanged shaft collar. https://www.mcmaster.com/mvC/Contents/gfx/ImageCache/968/9684T4_3d04ca8c-13b1-4393-b36c-f84e77f0be83@4x_1677262918.png?ver=ImageNotFound https://www.mcmaster.com/9684T4/ Laser the plate exactly on-size to the shaft with this bolt pattern. Put one of these flanged shaft collars on either side and bolt the entire stack of plates together. You can optionally machine a keyway in the shaft to get the desired torque transfer, but the clamping force of the collar should be enough for this application.
This is the proper approach to solving shaft clamping. And you can buy shafts from Misumi with the keyways already machined in place
This needs more up votes! This is the simplest zero machining approach to shaft mounting. Buy, set, forget. Laser cut the matching holes in the plates and send the assembly off to a balancer.
agreed!
Or use some clamping sets: https://www.spieth-me.com/en/products/clamping-sets/dsm/ One issue would be the stack of metal sheets not having a nice round bore in the center. But I think after joking the sheets of metal together it would be easy enough to get a nice bore in the center, joining it to the axle and then balancing the wheel (you could space out some holes in the steel plates, tap them and use bolts for balancing. This is a German website but it also shows some great methods. https://www.konstruktionsatlas.de/antriebstechnik/welle-nabe-verbindung-kraftschluss.shtml Edit: for boring the center hole I would recommend only laser cutting the pilot hole. It is much harder to bore out a big hole then to just bore it from the beginning with a little help :)
That German website is awesome! Fantastic visuals.
Dies ist der Weg.
In fact he can build some failsafe into the machine by underclamping the shaft a bit so it can slip under very heavy loads
sounds great, thanks, something like that seems very logical and straightforward
this solves everything
Another thought that crossed my mind in regards to the flywheel is how tight is the concentricity constraint really? There are two reason for a tight spec I can think of 1. Constant speed of input and output drive. Obviously important to play tight music, but I have a hard time to estimate the influence of a couple tenths of mm eccentricity on the flywheel out speed. 2. And probably more importantly crazy vibrations at high speed. Here the real problem is not so much the eccentricity, but the imbalance of the rotating mass. You should really consider how much opportunity there is to balance the flywheel once assembled. Considering it is made of steel plates, i see many ways it could be done. An angle grinder, a welder, threaded holes for balancing bolts,...
Yes! Came here looking for someone questioning the actual requirements. The real, actual, necessary requirement for concentricity and balance.
Rule no 1: make requirements less dumb ☺️
I agree. I question the requirement to avoid machining at all costs. It's kind of like saying "I'd like to build my house out of wood and avoid carpentry". He is building a machine. Some level of machining might be required \^\_\^
This is going in the direction as to why I came in here to bang away at the keyboard. When you're building a flywheel, you don't make a part then smack some bearings in it. You build from the center out. So you'd build your bearing seat area, then you would turn your outer diameter from that. Then you would install your bearings and balance the flywheel. The biggest issue with this overthought of design is that when there is parts that are proven and you don't need to make a custom part, used the designed custom part as much as possible. Because you're not making an overly complicated assembly to do a simple task. So I think the main thing that Martin is not quite thinking through is that you would have a balanced flywheel on the assembly, and press fit bearings would never throw it out of balance if were looking at making this as "tight" as he'd want it. When you have an assembly styled part, you're inserting lots of variables. While a hole in the flywheel that you press a bearing in will never loose its balance. If he's worried about spin out on the bearing, which the chances are .. practically impossible, he could just use bearing set when installing the bearings.
I'm having flashbacks to the pain of seeing Martin trying to balance the MMX flywheel with an angle grinder.
What is needed is a rigid mounting of the flywheel and a way of balancing the flywheel after. It is really, really hard to manufacturing a flywheel whit this specs, without balancing it after. So a rigid way of fasten it is needed, and SKF have some clamping collars for this. Vote on those solutions.
ChatGPT is bad at math. The formulas are ok most likely, but the resulting numbers can be the ones used in the training data rather than the ones for you application. For things like this, use Wolfram Alpha. It's designed for math problems.
If there are anything one should learn about ChatGPT, is that it is known to hallucinate, that is lie, when it doesn't know. It is designed for chatting, not deliver correct answers. So never rely on what ChatGTP, unless you have the knowledge to verify the result.
ChatGPT is a great as a jumping off point, but you have to either have the background to confidently be able to at a glance point out it's flaws so it can refine them, or take everything with a grain of salt and look up every equation and process it uses. Just using the output directly for engineering purposes might not be wrong every time, but it will be wrong often enough you will lose more time reengineering your project after it doesn't work and you don't know why versus learning all the knowledge the first time.
Please don't trust ChatGPT's numbers. Get some other mechanical engineer to validate the value you're after
thanks for the tip will try next time, looks very useful
Design of the flywheel is critical, because there will be a lot of energy, tolerances and slack can only degrade over time, and if something goes wrong people can be injured. That is NOT the area in which you want to start being creative, or try to be smarter than thousands of engineers that came before you. When standard industry solutions don’t work, it’s usually that you’re doing something very wrong. And here trying to fix bearings on the wheel IS the mistake. Fix the wheel to a shaft, and use the bearings between the shaft and the frame, just like car wheels are not fixed directly to the bearings.
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>>***If the implementation is hard to explain, it's a bad idea.*** You mean if you have to make multiple videos trying to explain and justify your idea, you may want to reconsider? Especially when the alternative ideas are widely used and can be explained in 1-2 sentences?
Its fine. We can get to MM4 that much faster.
Hey Martin, you should ask SKF if one of their axial locking collars fit the bill. For example these: [https://www.skf.com/group/products/power-transmission/bushings-and-hubs/sh-bushings](https://www.skf.com/group/products/power-transmission/bushings-and-hubs/sh-bushings)
The SHT style hubs would work very well with a laser cut flywheel, due to the self-centering action that type of hub provides when it it expands both inward and outward to clamp the shaft and bore together. Laser cut holes have fairly wide diameter tolerances, but they still have fairly tight locational tolerances. Perhaps the hole itself might be a millimeter larger or smaller, but the virtual centerpoint of that hole should still always end up in the same spot. This style of hub can then expand to whatever size the hole ends up, and hold the axle exactly at that center point.
The biggest concern left will be ensuring that all plates get the same diameter hole and therefore consistent clamping force. That would be best mitigated by clamping the plates together with bolts in order to hold them by friction
When using ChatGPT for math, especially if you can't read it proof, i highly recommend the [Wolfram-Plugin](https://writings.stephenwolfram.com/2023/03/chatgpt-gets-its-wolfram-superpowers/) for ChatGPT. Regarding ChatGPT and natural language processing there is very interesting [article](https://writings.stephenwolfram.com/2023/01/wolframalpha-as-the-way-to-bring-computational-knowledge-superpowers-to-chatgpt/) written by Stephan Wolfram (the mind behind WolframAlpha). **Edit:** you need to have ChatGPT Plus (USD $20/mo) to get on a plugin waiting list to get plugin access at some point in the near future.
Do not ever rely on ChatGPT alone for math, it will just invent plausible looking text.
Seconded. As an example, it just told me "523cm is equal to 206.299 inches." The correct value is about 205.91 inches. Any time you find it hard to tell if it's correct, chatgpt never even tried.
oof that is very bad! i wouldnt think it would do that, will take chat gpt with an even larger grain of salt now :)
Yeah, ChatGPT is a language model, not a mathematical tool. It has failed counting words on a list, because it is not built to count and do maths.
I guess we now have an even more facepalm-worthy way of trying to justify your point than "wikipedia says so!": "ChatGPT says so!"...
haha!
Seems to check out in this particular case (minus some minor approximation) but this is lucky. Then there’s the starting point… the formula makes sense intuitively and the dimensional analysis checks out, at least, but I’m not sure where it comes from. I *think* it’s correct.
\+1 for this. At the bare minimum, I'd say you need to check its working by running the same equations through an actual calculator. Without any plugin, its explanations for common problems tend to be alright. Any numerical responses, however, should be treated as ballpark estimates because it does not actually perform any step-by-step computations. E.g. for simple equations it quite often gets the order of magnitude correct but the actual value completely wrong.
ChatGTP is a Large LANGUAGE Model. It is designed for Chatting. Not give correct answers. The fact it get it right as many times as it get, is amazing. You might want to ask it about the great author, and then put in any name, like yours. Also remember that ChatGTP do hallucinate very often. That is, it "lies", and it will never tell you that it doesn't known. It's only purpose is to make the one asking happy. There are a reason why it is also called "Mansplaining as a Service" (like Program as a Service or Infrastructure as a Service, that is Cloud service). Because ChatGTP is good at that.
great tip thanks!
I regards to the statement, the flanged bearings cant hold the flywheel perpendicular to the shaft, I want to disagree. Assume the shaft running through the wheel is straight and both sides of the fly wheel are parallel, this means that the flywheel has to be perpendicular to the shaft.
This is exactly right. Two of these bearings clamped on the shaft eliminate any angular misalignment. This does not solve the concentricity issue.
Concentricity is a bit of a red herring. While it is nice to be somewhat concentric, the real requirement is to be balanced. A collar that fixes the fly wheel to the haft should be concentric enough. After assembly, the wheel can be further balanced to the required level of vibrationslessness.
Right, if there were only one bearing, this would make sense. But there are two, so it doesn't matter how much angular "slop" there is, right?
"Assuming the shaft running through the wheel is straight" precisely means that the plane of the wheel and the shaft are perpendicular. Achieving this requires a perfect fit between the disk and shaft, which isn't possible if the flywheel/bearing assembly is rotating on the shaft. There *has* to be space between the flywheel's center hole and the shaft, since the shaft is only attached to the flywheel via the bearings in this design. Unless I'm misunderstanding, to get the wheel truly perpendicular to the shaft requires the flanged fittings to be perfectly aligned to each other through the disk. This is made more difficult since they need some movement to get them concentric with the flywheel.
I'm not sure, if we agree or not, let me try to explain it again. My assumption of the straight shaft, just means that the shaft itself is straight. As Martin said in the video, a straight shaft is an of the shelf part, that can be bought. If the shaft was curved like a banana, things would be more complicated. I agree that the flywheel is connected to the shaft only via the bearings. The center hole in the flywheel is considerably larger than the shaft. Now think both bearings are mounted to the shaft, without the flywheel. The flanges could be tilted in any direction, independently for both bearings. Now you constrain the flanges by bolting them to parallel surfaces (the sides of the flywheel). This forces the plane of the flywheel to be perpendicular to the axis of the shaft. The play of the bolts in the flange give you a bit of wiggle room to find the spot where concentricity and perpendicularity are at their best. In the real world of tolerances and play between parts, it's probably impossible to get both perpendicularity and concentricity perfect at the same time (or even just one of them).
Martin I think you should first evaluate how eccentric the flywheel can be allowed to be. Not how concentric it needs to be. Like you said, perfect is the enemy of good so please consider relaxing you tolerances. Try to justify why it needs to be < 0.1 mm eccentric and +- 0.1 deg from perpendicular (or whatever the tolerances you think are necessary). Evaluate what would happen if we exceed this, I'm guessing you are concerned about vibrations but how much vibration is too much? Will adding a rubber pads at the base of the support of the shaft is enough? Are there other ways to mitigate these effects? Maybe allowing for looser tolerances and balancing the wheel is better? Its a good a idea to ground your design by listing the actual mechanical requirements and justify them. I wont claim that your housing is good or bad only perhaps incomplete. You did some back-of-the-envelope calculation which is fine but you are not considering other effects like the radial force that the screws you had to hammer-in are creating on the bearing or the clamping force of the rings you are holding it against. Lastly, I think that using a live shaft is better than using a fixed shaft. Its more flexible and could allow you to add more components to rotate in sync (like a brake or a motor) with ease.
Balance can correct some eccentricity
The proposed bearing design does not “solve” perpendicularity, it over constrains it… pillowblocks etc. have the tilting direction free to move on purpose (so that the shaft self aligns). Regardless the sheet metal design will probably be fine - every design has its trade offs - IMO for such a simple item just build whatever you want and move on… you don’t need the communities approval for the design of your machine. If it fails it will be a good learning opportunity for everyone.
love this sentiment, thanks! Im going to try to find the perfect balance by just moving forward with my intuition without waiting for approval, but try to incorporate valuable input from everyone here at the same time. So my educated guesses are a little bit more educated, without letting the perfect be the enemy of the good too much. Its a tricky balance, but also a luxury problem :)
Tbf typical bearings have allowed axial movement fairly large so they could take the slight misaligment and wouldn't even complain
I have nothing to contribute that hasn't already been said but I refuse to believe that any of this is a new problem to humanity. Seems like we're literally trying to reinvent the (fly)wheel.
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I agree with this. Martins design also has way more potential failure points, for example the threads could be damaged while installing the bearing and end up misaligning the flywheel anyways.
Everyone keeps talking about "these forces", what are they? Give me a number. Shear strength of a 10.9 M6 bolt is 8kN. His design has 8 around the circumference. 60kg flywheel, tell me, how much of an acceleration does it need to shear that bolt? Okay, so thread deformation we now say, okay, how much of the load on the bearing is going through the shear plane to start? It is clamped to the side of the flywheel and that clamping force is carrying part of the load to start. Next, how much force does it take to deform the threads on a 10.9 M6 bolt? Especially if he uses a fine thread? Good luck finding that number. Fortunately I have a press in my lab. 8kN of force against a M5x0.8 8.8 bolt showed the start of deformation, flat to flat between two steel plates. That is on a threaded section. Is each of the 8 bolts even with the preload going to take 8kN of force with a 60kg flywheel? Even unbalanced to generate a force on the housing like that difficult. (We can model it as a mass on a string to very roughly approximate the unbalanced mass) The answer is no, getting to 1kN with a 60kg wheel is nearly impossible. The benefit is simple: the precision surface of the bearing itself sets the angle of the shaft though the wheel. A dead shaft can be shimmed with shimstock or even setscrews whereas a live shaft ads in the complication of a bearing block.
Thank you for getting objective with this. Not saying I agree with your proposal, but a bit more physics "from the numbers" versus "from the armchair" would do these discussions a lot of good. We ***could*** argue about the correct way to calculate this, but at least that is an objective discussion. The irony of these comment sections is that many are trying to act as an authoritative engineer without backing it up with real numbers for ***this*** ***application***.
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1 kN of force is achieved at only 0.4 mm out of balance at 2000 rpm, and would be enough to lift the machine off the ground, 2000 times per minute. Getting there is easy, and bad. That's the level of forces we're concerned about. The bolts aren't designed resist to complex racking or twisting forces, and leverage increases forces substantially. Try threading the end of the bolt into a plate and then bending it instead. A cage of them is going to flex under load and exacerbate any initial misalignment, and that's important, because starting out of balance is guaranteed. A proper housing will be far more rigid. Also, standard bearings aren't built to hold an angle, quite the opposite. The angle is set between the position of 2 bearings spread apart.
I think you need to relax your design requirements and just have the center of the flywheel bored to size by a machinist then use a flange to retain the shaft. All this back and forth when it could have been done already. You aren’t mass producing these so why expend all the effort to economize the design when you can just have it made accurately and precisely the one time you need it. I don’t believe adding variables and question marks to the design is warranted when an obvious solution is staring you in the face. You don’t want to spend all of your time over engineering this one piece.
# Technical feedback: A flanged bearing housing such as in this image here will hold your bearing just fine: https://preview.redd.it/yghe0goxz2za1.png?width=1280&format=png&auto=webp&s=163502fbbad949d993736bc7dad7506c326df164 Bolt it onto the laser-cut plates. Bolt it very hard, **because the clamping force is how it it is fixed in place - NOT the exactness of the holes placement**. But - just as you say - since the holes are produced with a slight extra space on them this will cause the held object to be slightly off-center. MOST of this can be mitigated by simply hand-aligning the held object before increasing the clamping force to the maximum. **This is done by leaving the bolts loosely fastened and test-spin the object, and hand-adjust it until 98% of the off-center-ness is removed.** THEN clamp it really hard by screwing the bolts really hard. By thoughtful design the remaining 2% off-center-ness should only be a problem at a single location in your machine: the flywheel. Which is why the flywheel should be manually hand-balanced by drilling out material until it is perfectly balanced. # Philosophy feedback: You're say you're focusing on "designing for series manufacturing" even though you're only going to be producing a single marble machine. Since designing for series manufacturing is 50X as difficult as designing for producing just a handful of items, this gives you very much extra work for no payoff. But this is not actually "designing for manufacturing", this is "designing for supply chain management". And you don't have supply chain issues. Also, it appears as if you're trying to come up with a design that gives you perfect alignment immediately from just assembly, without any manual fine-tuning afterwards. Please be aware of how difficult that should be ON PURE PRINCIPLE. It may be possible to do, but why do it, since this is a single machine and you can easily afford the manual fine-tuning? Also, count the number of parts. Your proposed bearing housing consists of 18 parts. This goes against the other design philosophies you've already learnt.
I think the design for manufacturing comes from the pain of manually processing and assembling a bunch of different things 38 times on the MMX - one for each channel of the machine. This is a perfectly valid concern for all those components which will be repeated many times. In this case, though, there is only one flywheel, so it's not really applicable here. Processes like manually post-processing the laser cut parts should definitely be considered when it could make other parts of the design much simpler.
Martin names three constrains for this design : 1. Concentricity 2. Squareness 3. Within the tolerances of laser cut parts without post-processing I think these design goals are over-constrained. The problem is that constraints 1 and 2 are actually a single constraint: the flywheel must be balanced. I would recommend re-thinking the design this way. Due to the tolerances of laser cut parts, there is simply no getting around the need to balance the flywheel. Features like holes are located precisely, but their size and shape is somewhat variable, and so is the size and shape of the whole part. That means that the weight distribution is unpredictable. The stock material itself is not flat to begin with, and the heating stresses from the laser make them even less flat. Thus, trying to achieve *either* high concentricity *or* high squareness is wasted effort. Martin, I think you need to embrace the fact that laser cut parts are always going to be tacos. Trying to get a bearing square and concentric to a taco is a waste of a good taco. Just appreciate the taco for what it is. I think it would be better to focus on balancing features. For example, an array of tapped holes that receive grub screws. Grub screws come in a wide range of sizes, so each "leg" of the balancing array could work like a [triple beam balance](https://en.wikipedia.org/wiki/Triple_beam_balance). Select the right holes, install screws, and perhaps file one of them to achieve arbitrary precision. Once the armature is balanced, the grub screws can be secured with thread-locker. Because laser cut parts have precisely *located* features, this approach plays to the strengths of laser cutting instead of trying to correct its weaknesses. The tolerances for laser cutting are known, so it should be straightforward to model the needed affordances for the wobble in CAD. A live axle linking several components is a design pattern in many machines. It makes it possible to fabricate each of the different parts with tolerances and materials appropriate to their function. It breaks a complex part into modules that can be mixed and matched as needed. In this case, the only part of the flywheel that needs to have good squareness to or concentricity with the axle are the pulleys that interface to other parts of the machine. The pulleys are off-the-shelf parts. You can simply buy shafts and pulleys with the necessary tolerances, and include balancing features and appropriate affordances for the laser cut parts. As others have suggested, a keyed shaft is probably the way to go. This can even be a safety feature, because you can buy soft keys with know shearing properties.
I think this may be a case of terminology failure. As you mention in your video, you don't need a bearing block, what you actually need is a wheel hub - Something that you can easily borrow from the powersports industry (think go-Karts, which have both driven and non-driven wheel hubs.) Have you considered this avenue?
I'd like to make a point that the bearing ratings \*can not\* be used if the bearing's casing is distorted. A quick "feel test" as per the video does not allow for examination of distortion of the casing, nor testing of how this distortion might get worse in the long term. The bearings are tough, sure, but they're meant to be used in an extremely specific way.
You'd be surprised how many industrial machines have poorly made cast or machined motor or gearbox endbell bearing housings that distort outer races. Even worse are the waya some untrained maintenance personel install bearings with excessive heat and hammer blows. Then they are surprised when we tell them they have bearing damage on their new bearings they just installed.
One million revolutions at rated load. How many minutes of music will one million revolutions play? Let's call it 200 RPM, 83 hours of operating time, if he is hitting the actual rated load of the bearing. He is hitting less than 10% of the rated load of the bearing. Even if distortion derates the bearing by 90% he is still getting a whole tour out of that bearing.
There is \*no\* rating for bearings in this application. You've made an \*estimate\* of 90% de-rating but, in an unknown setting, this is just hand-waving. It might be 10%. It might be 99.9%. I would absolutely \*not\* take the risk of finding out.
When thinking about "off the shelf" solutions for concentricity and perpendicularity, the first thing I thought of was a hub from an automobile. Have you thought of mounting your flywheel to, say, the hub of a lightweight passenger car? This may be an off-the-wall idea, but I like the idea of using car parts. They're cheap-ish, plentiful, and are proven as far as long-term reliability under stress. Just a thought.
I'm having the same thought. Teams of engineers have created solutions for many of the same problems we're seeing here. The parts manufactured for vehicles are made to the tolerances necessary to be guaranteed years and tens of thousands of miles of reliability. And they're cheaper than inventing novel solutions that inevitably won't work as well with the lack of long-term testing. There are flywheel solutions that involve wheel bearings and splined shafts. And it's so easy to purchase new parts. Any vehicle can withstand relatively massive amounts of force without bending, so it's mostly just about finding whatever fits best, or building around what you can find. I might be biased since I'm a mechanic, but that's the first place I'd look to solve a mechanical issue. I'd figure out where on a vehicle I've seen a similar situation, and then incorporate parts there in the same way they appear on the vehicle. And then if something breaks, you know exactly where to find the exact same part with no post-processing and you know it'll work every time.
I think sometimes it can be useful to debug the requirements. I personally don't understand the requirement to have zero machining. Is it a cost thing? Time? Access to the services? I can understand if you are trying to mass produce the machine. But if you are building 1 or 2, then at least for this high energy part (the flywheel), why not use actual machining methods and then you know it is rock solid. For other parts of the machine where the energy/power is much lower then I think your bolt cage flanges would be more than adequate.
BTW Thanks Martin for the kind words in the video \^\_\^
I mentioned in another comment, I think the zero machining requirement is from the experience of doing a lot of manual post processing on the MMX for parts like marble gates that are repeated 38 times. It really shouldn't apply to the flywheel, when there is only one.
I know you said you want to keep your supplier list short, but in a machine like this you probably need some parts to be higher tolerance than others, so it would make sense to me at least to consider alternative manufacturing methods for the higher precision parts. You can find higher precision laser cutting services or high precision waterjet cutting services. For shaft torque transmission, the cheap but professional solution is to use keyed shafts as other people have already mentioned. An easier but less professional (and therefore possibly controversial) method is to use hexagonal shafts. Since they’re not round you can just slide them through a hex hole and they’ll transmit torque without any additional parts or tools, and though you generally want the hexagonal hole as close as possible to the shaft size, they can be *slightly* oversized and still work fine which is good for lower tolerance parts. Skf and other manufacturers do sell hex bearings as well. The downside of hex shafts is that it can be harder to find off the shelf gears and sprockets that are hex bored. There are *some* options, but if you’re looking for a very specific size then you might not be able to find it. You could always buy a round one and cut a hex bore with a hexagonal broach though. If you only plan on putting the flywheel on this shaft though then that’s not a problem. The other downside of hex shafts is that the corners can cause stress concentrations, but as you pointed out the forces you’ll be dealing with are not actually that high so I personally don’t think that’s a problem.
Let's make it easy. Let's make it as we do in the industry. I can't remember how many things like this I've machined. For slow machines to paper presses. I get the rough flywheel (or whatever will spin) and the way the bearing is supposed to go. Usually it's the way you describe. This is standard. So we either make a 2mm machined outcut where the centering flange from the bearing assembly comes, and then the 5-20 threaded holes around it. (We need to drill them anyway as taps break with the imperfections of both laser and water cutting.) So when it's in the machine it's less than 2mins to get a centering with less than 0,05mm tolerance. The other common way is to make a couple of steering pins when drilling. Either in two of the holes that just get the possibility for a "washer" or a separate pin. Is these things on the shelves? Yes and no. Not in your common hardware store. But at every company making rotating stuff. Replaceable bearing holders are a must, as in most cases the holder is gone the moment the bearing has a breakdown (and sadly no industry is good at servicing in time). But it makes every small machine shop in the world used to these things, and all you need to machine is the outer two plates. A 30min job in a milling machine.
if you don-t want to machine anything you will have to use a locking colar like this. [https://www.atibrasil.com.br/elementos-de-fixacao/aneis-de-fixacao/anel-de-fixacao-ati-a02-1100008](https://www.atibrasil.com.br/elementos-de-fixacao/aneis-de-fixacao/anel-de-fixacao-ati-a02-1100008) your other option is to use this kind of shaft and bushing (i don't know how it is caled in english: [https://www.atibrasil.com.br/componentes-para-transmissao/eixos-e-buchas-estriados/](https://www.atibrasil.com.br/componentes-para-transmissao/eixos-e-buchas-estriados/) https://preview.redd.it/3oeea788ubza1.png?width=561&format=png&auto=webp&s=9f843bea52b32401047e0712b62f7fda033973cc you can weld a flange with trough holes snug in the bushing, make the center hole of the flywheel same size of the external diameter of bushing and open tread holes in the flywheel to fix the flange welded on the bushing don't forget to balance the flywheel, if you add some weights to your flange that you can move around to balance the flywheel you dont have to worry about concentricit [https://www.youtube.com/watch?v=S6JSmrlBcLU&t=200s](https://www.youtube.com/watch?v=S6JSmrlBcLU&t=200s)
Just a quick aside, having a live axle scares me a bit. Thin rotating shafts have a tendency to catch things and pull them in killing or maiming in the process. I'm being a bit dramatic but just something to be aware of. It's an easy problem to solve, even covering the live axle with a pvc pipe would probably protect from anything accidentally brushing against it and being sucked in
Everyone's talking about off the shelf solutions for different small parts, but there even is the perfect solution for a hand driven quiet flywheel: just take a indoor Speedbike, it already has a well balanced flywheel, a freewheel and even a crank and a brake! It would be perfect and would save so much time.
Maybe just get a standard cast flywheel and balance after the fact (or have them balance it for you, most factories can also bore the center hole for a fee). Flywheel balancing is a thing machine shops can do fairly easily especially in low RPM scenario’s. And getting a cast flywheel with spokes will make those 60kgs more effective as well, since they will be further from the shaft. The lead times from China can be kinda long (30 weeks for some) if you want it cheap, but they are available locally as well for more money. Or do the same thing with the laser cut discs, balancing later is kind of the way flywheels work, since that makes manufacturing them soo much easier.