Between my P2V+ and P3S, I've only had one motor problem that also blew the ESC board. My fault. Got some sand in it upon landing (another reason I now hand catch). They are brushless motors, wound with a continuous string of wire, operated by electrically rotating a magnetic field to make the motor turn. Almost nothing to go wrong. If you're having a motor problem, likely fault is the ESC board or driver(s). Swap out the motor with the one on the adjacent arm (that is, swap the CW motors, or the CCW motors). If the same motor still doesn't spin right, probably a bad motor. If the swapped motor doesn't spin right in the same arm as before, then an electrical problem. Keep dirt out of them and prevent a tip-over on landing and they should last a long, long time.