So upon testing my robot a couple days ago, one of our motors somehow suddenly self-stalled itself and thusly stalled the other motor (in the drive train).
Upon removal and inspection of the first motor, manually turning the motor was very difficult; not enough resistance to cause me to break the motor/gears, but there was definately something stopping the motor from turning. Removal of the internal gears and powering the motor via the 9-volt still causes the motor to self-stall.
Inspection of the actual motor (without removal from the casing) reveals no sign of electrical shorts between the red and block wires. Turning the actual motor has a considerably larger force than a normal motor. Has anyone else had this problem, and if so, what was the cause?
Our motors were not running well also. I went to my local auto parts store and bought a can of electrical parts cleaner and got 60W shock oil from a hobby store. I cleaned our the motors with the parts cleaner and drained it then lubed it with the shock oil. It may not help you now, but it should make your motors last longer and run smoother if you do some maitenance on them.