JVN Build Tip: CIM Pinions

The CIM motor has 0.75" diameter protrusion on its face which is GREAT for piloting (keeping the CIM centered where you want). Relying on the (2x) 10-32 mounting screws will work, but won’t result in as consistent a mounting. If you have any slop in your mounting holes the CIM could shift, resulting in a loose or tight gear mesh.

Typically, people use a 12-tooth or 14-tooth 20DP gear as a CIM pinion (see KOP transmissions).

One of my favorite tricks? Always opt for the 12t pinion. The 12t gear fits through a 0.75" hole while the 14t gear does not. This allows you to swap a CIM motor in/out without removing the pinion gear. You can have CIM motors on-hand ready to swap in.

Then again… I’ve never had to remove a CIM motor except to work on something else… Maybe this isn’t such an expert tip after-all.

As always… good luck in 2011!


Originally posted here: http://jvengineering.blogspot.com/2011/01/jvn-build-tip-cim-pinions.html

Another great tip John. I’ve had to remove far more than my fair share of CIM motors and it’s a real pain every single time the pinion is not smaller than 0.75" OD. However, sometimes I don’t like using 12 tooth 20DP gears because I believe they are undercut. Not a big deal really, but I just feel the 14 tooth gears mesh a bit nicer. I really wish we could get a bigger boss on the face of the CIM, like 1" maybe.

Also, for the pinions, which see the most cycles of operation, I like to use Martin S20XX series gears, as they’re slightly harder and I’ve experienced some odd wear issues with the AndyMark pinions. Of course, if I wanted to I could probably harden the AndyMark ones.

Totally agree about the 12tooth pinion! Even for the one time you assemble it, it is worth it to just pass the entire motor through the 0.75" hole and tighten it in place.

I can’t recall a time where I’ve switched out just a CIM motor, but I can imagine getting to that step and having to take the pinion off would be a pain!


As an alternative to using a smaller pinion than you want, you can make an adapter bushing for the CIM 3/4 boss and make a larger centering hole to accommodate the larger pinion. Of course, you are limited to a max diameter on the bushing by the edge to edge distance between the 10-32 FH screws to mount the CIM. In addition, you should have several CIM/Bushing motors set up so you are not “pressed” to remove a pinion if a swap becomes necessary. By the way, we have never lost a CIM motor, and have done a review of them in the past after a long competition season and post season play, and have never been disappointed in their durability.:slight_smile: :slight_smile:

Another tip I’ve been asked to pass along: CIM motors aren’t designed to handle significant cantilevered load – make sure you’re not using them in an application where they have significant side load on the shaft.

Luckily, most people don’t really do this so it usually isn’t an issue.

Could i get a link to the gears you like to use