pic: 3 CIM PTO With Break

Any reason as to why you have such a huge gap around the CIM motor’s raised face?

If its the spot I think you’re talking about, I would bet its so the gear on the CIM (which appears to be a bit larger than most) can be taken off with the motor… but that’s just a guess.

Yup. That’s right.

If you use the 12t pinion instead the 14t it fits in the profile of the .75" boss, so this is guaranteed. And a smaller pinion gets you the needed reduction in fewer and smaller stages. But 14t may be appropriate in this case, I wasn’t around for your decision-making process.

I was thinking about doing something like this, but I couldn’t figure out how to do the gear spacing. Because I didn’t know the spacing for different gear-sets, I couldn’t choose the right ones. How did you avoid that issue?

In FRC a lot of people use the following formula to calculate gear center to center dimensions:

C to C = ((N1 + N2) / (2 * DP)) + .003

N1 and N2 are the number of teeth in the two gears you’re meshing, and DP is the diametrical pitch of the gears (which in your case is 20).

See this thread for more info:

we had something similar to that this season we had a 3 cim pto with a two speed and also a brake. https://sphotos-b.xx.fbcdn.net/hphotos-frc3/978033_678745172142135_1347743242_o.jpg

Screws aren’t really meant to take shear force, nor are they intended to locate features. If you use a large center hole for the CIM, the hole will no longer be able to constrain the motor as intended. Depending on how large your clearance hole for the 10-32 mounting screws is, you could end up with as much as .005" of play in either the closer or farther directions. This is obviously optimal for neither gear efficiency nor backlash, and completely mitigates the effect of adding .003" between gear centers. You should really reconsider the benefits of a large boss hole, and whether or not they outweigh the negative consequences.

Yup. Saw that at the NYC regional and as the driver for my team, I wished I had one. So I made one lol.