[fox46]

Well at 20% of stall current (130A) and 12V, you have a power consumption of ~300W. To put it in perspective, thats about the same amount of heat generated by 10 soldering irons. This heat is localized in the armature and brushes of the motor which can melt the laquer that insulates the windings and overheat the brushes. If you insist on stalling them, I would make sure you have a couple muffin fans blasting air into/out of the motor case as much as possible. But again, stalling the motors is a poor engineering practice. I would strongly suggest you modify the design to include a ratchet, one-way bearing, worm or similar gearset to limit backdriving.