[KenWittlief]

At this point in the design cycle I would recommend looking at your drivetrain design, to keep the motor RPMs high, so you dont need a fan

it should be easier to design in one more set of gears in your drivetrain, to get the motor RPMs up, than to design for bad design and fabricate monster heat sinks and fans.

You can run those drill motors all day long, at their intended speed and load, and they will not get hot.

Every team should take a motor apart (one you dont need anymore) and see whats inside. The heat that is generated in a stalled motor comes from the armature, the part that spins. This does not touch the case of the motor at all, except at the bearings. You will also discover the drill motors and FP motors have blowers built into them, by the commutator. This blower does an excellent job of pulling air through the motor where you need it: across the windings (as long as you dont block the openings where the air comes out).

If your motor gets so hot that you cant touch it, and it smells like burnt varnish, the armature windings inside must be almost glowing! Blowing air across the case will only cool the magnets that are in contact with the case. The windings on the armature will continue to cook.