CIM to 3/8" Coupling?

Hey all,

I am currently working on a Swerve Module, mostly for practice and fun. My issue is that I’m wanting to use a CIM as the drive motor with the CIM shaft coaxial to the driving bevel gear. I’m hoping to use either the 3/8" Hex bore 15t bevel gear from WCP or a similar 3/8" hex bore bevel gear, but I’m not finding many options for going from the 8mm CIM shaft to a 3/8" hex bore. I can use a VersaPlanetary with the 3/8" hex output, but was wondering if there was something simpler or shorter for this application.

Thanks in advance.

Andymark and Vexpro offer shaft adapters that take 5/16" keyed CIM shaft up to 1/2" hex.

My team has made similar adapters using 3/8" hex stock drilled through in an accurate lathe chuck, then cutting the keyslots through by hand with a Dremel. The 2mm key height needs to be reduced by about 0.01" (filing in a vise works) so it won’t extend beyond the 3/8" hex.

How will your bevel gear set-up handle thrust load on the CIM?

I’m a big fan of the adapters you mentioned, but I didn’t think a similar adapter could be made from 3/8" hex due to the walls becoming too thin, but if you’ve worked with them and they work, that’s great. Do you use the aluminum hex shaft from Vex, or do you have steel shaft for this purpose?

Also, I’m not quite sure I understand what you mean with the thrust load. Do you mean the force pushing up directly against the CIM shaft?
If so, I was planning to use 1 or 2 thrust bearings from McMaster Carr on either side of the plate that the 3/8" shaft would pass through; one bearing between the driving bevel gear and the wheel carriage and one bearing between wheel carriage plate and the base mounting plate.
That’s the current plan, but I really haven’t gotten far enough to worry about it.

Yes, that’s what I meant by thrust load. You will need a way to keep the bevel gear from sliding on the shaft adapter, and to keep the adapter from sliding on the shaft.

We used Vexpro aluminum 3/8 hex shaft stock, but I think steel would work also. CIM torque is not high enough to require steel. Wall thickness is not much, about 1/32", but it is enough if you can cut the key slot for a tight fit.

Ok, thanks for all the help. Currently, the bevel gear can’t slide at the moment due to its position in the system, but I’ll have to figure out to keep the shaft from sliding up and down. I’ll figure that out when I have a better idea of the spacing and where everything will go. I’m wanting to make sure that the sliding motion of the shaft is isolated from the CIM enough that it can take a decent amount of impact without that force being transferred to the motor.
I’m not trying to make this the most compact or lightest Swerve module, I more want it to be able to take some abuse without dying on the field.
But again, thanks for the input.

Center Drilling a 8 mm hole (.315) in stock that’s .375 hex won’t leave much (.03) wall thickness across the flats. You would then need a 2 mm keyway broached into the corner of the hex. If your robot gets hit hard in a defense game, that’s a failure waiting to happen.

I would suggest going with a different miter gear on a larger round shaft. Look at SDP, Martin, & Boston for alternate miter gears. Adding a keyway for a miter on a round shaft is trivial on a milling machine.

Another advantage of round shaft is there are smaller ball bearings available and you can use needle bearings. There are no 3/8 hex bearings smaller than R8 (1.125 inch OD). That will make for a larger steering tube.

+1 on using smaller round shafts. I’ve done this on some of my bevel-beside-wheel swerves, and it ends up making the whole setup lighter and nicer.

If you have access to a 1/2" hex broach, it might be better to just drill and broach the bevel gear and use a standard CIM to hex adapter. Just a thought.

So I have not been able to work on the designs much recently, but I think I’ll actually be putting the CIM through a VersaPlanetary, and so I’ll be able to use either size of hex output, or a round shaft output. But I’ll certainly consider the suggestions you guys made.