I’m designing a west coat drive for my team and am wondering the best way to keep the wheels from sliding off the axle. We don’t have the manufacturing capability to machine snap ring grooves, so I was wondering what the best alternative would be.
Thanks,
Jack
8230 KoiBots
There’s a couple of decent options.
Load one of those up on the outside of the wheel. Cheap, easy to install… but you need to crank down hard, and there’s a size/weight penalty (if minor).
The other typical one is if you can drill a hole down the center of the shaft, tap it, and screw a washer in with loctite.
Usually, teams place a spacer between the outer bearing on the rails and the wheels, and then drill a concentric hole on the end of the shaft, tap it and screw a washer into it to hold the wheel on. Remember to use loctite and some teams use special nylon patch screws from McM or alternative to help the screw stay. Also, shaft collars can work, but are heavy.
This is the method we use. As you can see it is also more compact than extending the hex shaft through the wheel to attach a collar around it. As long as you remember the Loctite it should be bulletproof (and we just use the blue).
You can use a dremmel to cut the grooves.
… If you’re perfect about it. I’ve done this on a lathe with proper jigging (putting grooves in hardened shafts means either use abrasive methods, or carbide)… the results are less than ideal. Snap rings are finnicky items.
Just tap the ends of the shaft. Use lock collars in the middle of shafts where you want things to be assemble-able (but once assembled, the collar could come loose and you’d be OK). Use spacers to take up slop.
Or just directly tap the ID of thunder hex. No drilling required.
It’s worth mentioning that a hole for a retaining screw need not be perfectly concentric. A hand-drilled hole will do just fine for a vast majority of situations.
If you don’t have a lathe to center drill a shaft, you can very easily create center lines using a home made jig, printed jig, rulers, etc and then punch your center before drilling.
can help when you don’t have a lathe to add a perfect concentric hole in a shaft.
I don’t know if I’ve seen it on a FRC robot, but there plenty things that hold their wheels on with a washer and cotter pin (if side drilling your hex shaft is simpler for you).
Bear in mind, these help you make a concentric hole, not necessarily a coaxial hole.
Better than nothing for teams without access to a lathe. For FRC purposes, good enough.
If the hole is only being used for purposes of adding a screw for wheel retention, it doesn’t need to be either concentric or coaxial.
Can confirm, tapped thunderhex to hold wheels on. The center hole is definitely not concentric or coaxial. Wheels stayed on. Would recommend. Minimal drilling required - you could just send the tap in as is but I recommend drilling it to .201 first because of tolerances on extrusion.
Assemble the drivetrain, turn on the motors and cut a snap ring groove with a saw. Works every time.
We use this method, but no Loctite and I don’t even think the screws have nylon patches most of the time. If you get them really tight, they generally stay fine.
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