[sanddrag]

For drive gearboxes, 20 diametral pitch gears (made by Martin) are pretty much the norm for FRC. You can get them from Small Parts or Motion Industries. Small Parts usually always have them in stock but Motion is usually a bit cheaper, especially on the larger gears. 24 pitch would work too but they are less common. For low loads like the first stage of gearing off the fisher price motor, 32 pitch is good. 32 pitch would most likely hold up on the CIM too but why not standardize it all at 20?

For face width, we've always used 1/2 but 3/8 is fine.

Also usually these gears will have large hubs which you should/could turn down or face off to save a lot of weight. You can also take some material out of the gear too by making it thinner in the area between the teeth and the bore, or by drilling holes.

Let me know if you have any more questions.