[daltore]

I would also suggest the Fisher Price (Johnson Electric) motors. They're 1/3 horsepower a piece (2/3 the power of the CIM, which is 1/2 HP) and runs at 15,600 RPM. Shooter wheels at normal diameter seem to work pretty well direct-driven from CIMs (5,000 RPM), so gearing the FP's down by a factor of 4 or 5 should probably be good (because of the less torque of the motor compared to the CIM) for about 3-4 K rpm. If you can't make a gearbox, Banebots makes some good ones that fit well with that kind of reduction range, and there's also the planetary transmission from AndyMark (3.67:1). With whatever gearbox you use, if it's low reduction, make sure you don't stall the motors, because those FP's have a lot of magic smoke in them, and are quick to release it. When you have a third of a horsepower in such a small motors, there's a trade off in the pounding it can take. They can burn up without ever tripping a breaker.

Alternatively, if you're using the FP motors already, you could use the Banebots motors. They're less powerful (about 1/4 HP), but run faster (17,500 RPM) and don't burn up AS EASILY (that's not to say they don't burn up). Banebots sells gearboxes for these with the motors only, because the motors themselves are only about $5.