The reason why you can NOT stall the DC gear motors

When motors stalled, both stall current and stall torque will be very high. The high current will burn or damage the commutators and brushes, the high torque will damage the gears. We suggest you apply current limitation on PCB to prevent stalling. If motors have to stall in your application, please contact us, we will make an evaluation per your specific stall situation, and give you more suggestion and offer you solution.