Gear Face Width

[scottandme]

Originally Posted by asid61

Wow, that's a much more dramatic effect than what I have experienced. I stand corrected.
I think I said what I said, than 32p does not save space, because I'm used to designing side-by-side CIM gearboxes. This makes 32p impractical, because you need a minimum center-to-center distance of 2.56 inches anyway.

Sure, but only for that one usage case (2+ CIMS on a single gearbox).

If you're using non-CIM motors, or only 1 CIM, you can realize those gains.

See here for an example: http://media.team254.com/2012/08/gearbox.jpg

[Tristan Lall]

Originally Posted by Chris is me

You are right in that the first factor is the shaft size - obviously the pitch diameter can't be smaller than 8mm.

For the more adventurous, you can turn down the shaft diameter, and add an aftermarket gear (like the ones for the RS-series motors). You could also cut gear teeth in it directly.<sup>1

1</sup> For the most adventurous, if you really want to go crazy to prove the point that we aren't limited by the shaft diameter, and aren't averse to some creative fixturing and metallurgy, you might even be able to machine it, then harden it in place, and finish-grind the diameter (to maintain concentricity) and the teeth (to clean up the profile). That would permit a very small, strong shaft. This isn't remotely easy or cheap, and it's virtually inconceivable that any FRC team has ever tried it. You'd need a lot of very direct heat and a lot of heatsinking ability to avoid cooking the varnish in the motor or demagnetizing the magnets, while still changing the phase of the steel at the tip of the shaft. Then you'd need to quench it fast. And finish grinding of gear teeth essentially requires a custom fixture, which you'd have to build. (Note that if the next set of FRC rules have a definition of modification that allows disassembly of motors, this becomes a fair bit easier.)

[asid61]

Originally Posted by Tristan Lall

For the more adventurous, you can turn down the shaft diameter, and add an aftermarket gear (like the ones for the RS-series motors). You could also cut gear teeth in it directly.<sup>1

1</sup> For the most adventurous, if you really want to go crazy to prove the point that we aren't limited by the shaft diameter, and aren't averse to some creative fixturing and metallurgy, you might even be able to machine it, then harden it in place, and finish-grind the diameter (to maintain concentricity) and the teeth (to clean up the profile). That would permit a very small, strong shaft. This isn't remotely easy or cheap, and it's virtually inconceivable that any FRC team has ever tried it. You'd need a lot of very direct heat and a lot of heatsinking ability to avoid cooking the varnish in the motor or demagnetizing the magnets, while still changing the phase of the steel at the tip of the shaft. Then you'd need to quench it fast. And finish grinding of gear teeth essentially requires a custom fixture, which you'd have to build. (Note that if the next set of FRC rules have a definition of modification that allows disassembly of motors, this becomes a fair bit easier.)

Actually, you can open up the CIM and remove the shaft for machining. I distinctly remember one team did this. I think is was to allow CIM mounting to a versaplanetary.

[Tristan Lall]

Originally Posted by asid61

Actually, you can open up the CIM and remove the shaft for machining. I distinctly remember one team did this. I think is was to allow CIM mounting to a versaplanetary.

There are two issues: firstly, the definition of modification and secondly, the utility of removing the rotating portion of the CIM.

Modification isn't straightforwardly defined, particularly because it's difficult to account for the cases where something is disassembled, and then reassembled in a functionally-identical way. When the assembly was apart, it was clearly modified, but it is arguable whether reassembly restores it to an unmodified state, leaves it in a functionally-identical modified state that negates the illegal modification, or leaves it in a functionally-identical illegally-modified state.

As for removing the CIM shaft, although it's straightforward to open the motor up and detach the rotating parts from the fixed ones, I don't recall it being practical to remove the CIM shaft from the armature. As a result, overheating the varnish is still a concern (but overheating the magnets would not be). But you're correct that this would nevertheless simplify the process significantly.