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At stall, a motor has no back EMF... The back EMF is caused by the turning of the rotor. This is exactly why it does heat up so much, because when there is no back EMF, the current is only limited by the internal restance of the wires. In other words, the motor is simply a resistor when stalled. Again the back EMF is caused by the rotating rotor. When the rotor spins fast enough that the induced back EMF is equal to the forward EMF, the motor has reached it's "no load speed" or "free speed".
In stall, the amount of heat generated is the power applied to the motor (voltage * current) since ALL this power is wasted since the mechanical power produced is zero (torque * ang. velocity = 0).
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Systems Engineer - Kiva Systems, Woburn MA
Alumni, Former Mechanical Team Leader - Cornell University Robocup - 1999, 2000, 2002, 2003 World Champions
Founder - Team 639 - Ithaca High School / Cornell University
Alumni - Team 190 - Mass Academy / WPI
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