So we figured - we have machining resources, and we’re not afraid to use them! Why not make a few?
We have supplies and tooling on hand to make a few, and it’s a short drive to pick up more materials. Thanks to Nico Machado (3309 alum, @nxmq99) we have an extra set of hands and more access to the shops here at WPI.
So what we want to know - would teams be interested in a limited flywheel run? We’re looking at something with the following tentative specifications:
Probably machining simplicity. I can’t speak to how they’re planning to produce parts, but eliminating the need to broach with an arbor press eliminates a (probably manual) step in the process, which could speed up the entire production run.
Is there any reason not do have just a straight hex bore?
Exactly as Jon said - machining simplicity. We can crank these out with two mill ops if we have a bearing bore, while a hex bore would require buying a nearly $300 broach and making poor Nico get on a press.
Plus, not everyone uses 1/2" hex bore; we figured it would be most useful to let teams have the option of what shaft to use, including dead axle support.
Extremely pocketed! Plenty safe though - we’ve done a whole bunch of FEA and soon some real world testing, both the 6" and 4" version are rated up to around 6.5k RPM w/ a FoS of around ~8 (we’re being careful on this one).
Sure thing! When we’ve finished a beta unit or two we’ll do some testing and see what these can take in the real world. We’re still not sure what sort of balance we’ll be able to achieve, which is why we’re initially hesitant to rate at those sorts of RPMs, but we’ll update our specs once we have some real-world numbers.
Ran the current CAD through Ansys FEA at a few different RPMs, simulated centrifugal force as well as shock loading (full deacceleration over 0.1s). FoS is calc’d from yield strength of the flywheel material (1018) given stress reported by the solver. We’re tuning some parameters for maximum MOI:mass ratio, so numbers might change a bit - we do hope to be able to rate at least the 3.9" flywheel to the low five digits RPM-wise.
Next question - you’re giving a common hole pattern - but are any of the hubs available for that hole pattern capable of holding that wheel at that high a speed?
You could wire edm a hex, but it would be quite an adventure to mill one. In theory you could drill out the inscribed circle, and then go in with a very small (easy to break) end mill, however, It would probably cost them more then buying the hex broach in the end, and it would never be a true hexagon.