arduinopi:
what will over voltage of a DC motor do? like say I have a 12 volt motor and run it at 24 volts. What exactly happens when it "burns out"? too much heat?
if so can I run it in cold temperatures?
The startup current and stall current will both double, and the heat dissipated within the motor at startup and when it is stalled will go up by a factor of four. It's conceivable that this would be enough to burn windings out.
The mechanical issues from doubling the free running speed have already been mentioned. I would have thought that if the motor was safe and reliable and durable at the free-running speed with 12V then running at twice that speed is unlikely to do anything catastrophic in the short term.