I had bought Pololu 30:1 HP Micrometal Gearmotors last year in November. Recently a strange behaviour has been noticed in a motor mounted on my robot. The motor ran perfectly for a short period of time (about 15 minutes with regular breaks of 2-3 minutes each time the two motors heated), but after that it got jammed. I detached the gearbox and found out that the small gear situated behind the gearbox was not rotating. Instinctively I slowly pulled it outwards marginally, and it started rotating again. I reassembled the motor and continued my work, but the same problem was observed, and after a similar period of time, in the other motor also.
The only change I have incorporated in the PD based code for my line follower robot is a functionality of reversing the appropriate motor when the error becomes too high or too low.
I would appreciate a solution, and would also like to know about the reason for this problem.