CIM motor to 1/2 Hex shaft coupler

So I have researched this a bit on Chief Delphi and the internet but did not find an answer.
Is there a coupler out there that will connect a 8mm keyed output shaft to hex shaft?

I have seen the following answers in other post

  1. Drill out the hex shaft to 8mm and put in a set screw
  2. Use hubs to couple the two (we have used this, but it is large)

I did find this part but don’t know if it is the proper dimensions, will call tomorrow to find out.
It is from a soft serve ice cream machine

Anyone else have an idea ?

Thanks in Advance

Is this what you are looking for?

This may also be of interest:


Have used before. Good shaft adapter.


Depending on your situation, you may want to go with a versa planetary gearbox from vex with no reduction stage. That will give you some convenient mounting options. If you plan to mount the cim directly to your robot then the option above should work.


In addition to the commercially available adapters, if you have a lathe, an 8mm drill bit, and a 1/8" keyway broach, you can turn any chunk of hex into an adapter.

It’s nice to have those things, above, for making your own, but it’s nice to have the COTS solutions available for pretty cheap, too.

I realize others have given you the proper part but your setscrew method reminded me.

If you want a more custom solution, where you connect your motor directly to a longer shaft, setscrews are the way to go.

There’s something called a “dog point” setscrew. Get the appropriately sized one that fits into a 2mm keyway on the motor shaft, and completely forget about slippage.

Something like this could work: (the keyway in the CIM shaft is actually 2mm).

I can’t disagree more. Ever since we slipped a set screw on our climber in 2010, we’ve never trusted them for any torque-producing application; we always use either keys, shaft geometry (square/hex), or roll pins – and we’ve never, ever regretted that decision. Set screws can come loose, so pick an option that literally can’t.


So the first one turns the 8mm shaft into a 1/2" hex shaft.
We have used the 2nd one and bolted it to a 1/2" hex shaft hub
but we were looking for something more compact.

The coupler would be female to female 8mm keyed shaft to 1/2" hex shaft.


Pandamaniacs (and perhaps some friends I can’t speak for) will use the shaft adapter Nathan linked with AndyMark’s 1/2" hex aluminum spacers. We ordered a bunch of the 1.2" pre-cut ones to save time. Not 100% sure how we’ll constrain the spacer along the shaft, but if it doesn’t just naturally fit then I’m hoping a dab of CA glue will be enough. (There should not be much, if any, load along the shaft’s axis on our shooter.) Worst case, it’ll be shaft collars.

(Yes, I worked at AndyMark.)

If you don’t have the lathe or broach, but can get an 8mm bit, and a saw, you can do something similar with a couple of shaft collars and thunderhex (pre-bored for #10 through bolt) shaft.

  • Bore out the ends of the shaft to 8mm, to the depth of the CIM shaft length.
  • Saw along a diameter of the shaft to split it at both ends,
  • Slide on a couple of shaft collars with whatever other hardware you need on the shaft between them.
  • Insert the CIMs in each end, move the shaft collars down to the split, and tighten.
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Did you check out the link he posted?

We’re referencing these particular setscrews. They don’t rely on friction to keep a hold on shafts, as these physically engage into the keyway. 2-3 of these on a shaft is more than secure enough for a first stage shaft.

While setscrews may have been an issue for you in the past, that doesn’t mean they’re utter garbage. There’s plenty of good applications for setscrews, some of which that even transfer torque. I’ve had my fair share of mechanical design with high reliability systems, and I can’t tell you how many setscrews I’ve seen. It sounds to me like a poor design choice over a poor fastener design.


I personally try to stay away from setscrews, but they’re a tested mechanical solution and have their place. They’re extremely cheap and fit in small spaces.

I would never use a setscrew without some sort of positive locking mechanism (like the extended point, or a BIG flat on the shaft).

It is legal to modify the shaft of a motor in FRC, so grinding a flat or drilling a cross hole is an option. The CIM shafts aren’t very hard so they can be filed or drilled with some care. I’ve used worn-out CIMs for personal projects and was able to hand file some really nice flats on the shaft for belt pulleys.

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Another thing you can do is drill out to 8mm, then cut a slit down the middle with a band saw or something. Then, clamp it onto the output shaft with a shaft collar. We’re using it on Falcons for our prototype shooter with no issues.

You have the keyway in the output shaft

This is very similar to how pinions are applied to motors for use with VersaPlanetary gearboxes.

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To be that guy, a looooot of COTS suppliers and people use set screws incorrectly. The slightly pointed screw into a round shaft is no bueno obviously, but a d-shaft and flat bottom set screw with a lot of surface area and threadlocker is very nearly as secure as a proper d-shaft and bore. Of course, if there are methods with more positive engagement and fewer parts you should pretty much always go for them.


Slightly off topic, but because you are direct driving the shaft, make sure you have 2 bearings on the shaft for support and are well aligned, so you don’t put radial loads on the motor. That’s a quick way to destroy your motor.


Came here to recommend this exact solution. You can even use a hose clamp if you want. This is far more robust than you will need, as janky as it sounds, and can be done by essentially any team with a lathe, perhaps even with just a drill if they are drilling out a shaft that already has a hole in it (since concentricity is a must).

This is obviously better than the worst set screw applications, but this is still unacceptably risky / for FRC, and I would never recommend it in this application.

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