[Jon Stratis]

Yes, FRC motors can cook themselves, under some circumstances. Mostly, when they stall (don't move) while being powered. With some motors, this can even happen on the robot before the breaker trips.

It's all a question of heat dissipation. Moving that much current through a motor will cause it to generate heat. Some motors, like the CIM motors, have significant thermal mass, and can absorb a lot of heat - stalling them out for short periods is usually ok, which is why they're almost always used on the drive train. Other motors, like your typical 500 or 700 series (Banebots 550, 775, for example) don't have that thermal mass. Instead, they rely on built in fans to draw air through the case to dissipate the heat. Those fans only move when the motor is moving, so when you hit a stall condition and are still generating heat, there's no where for it to go... it builds up quickly and poof, your motor is dead.

Make sure whatever potentiometer you're using is rated to carry significant current- most of them aren't! A better (and much easier) solution is to get an old drill. Take it apart, remove the motor and hook up an Anderson connector on one end and whatever standard connector you use on your motors on the other. You can also stick a breaker in the middle somewhere. Then you can easily plug in a motor, control it's speed dynamically, and even switch between forward and reverse! Plus, the internals are going to be able to handle the current in a vast majority of cases.