[Jonathan Norris]

We ran into a similar situation with our arm, we designed it to work with two FP in the 256:1 gearbox's (assisted by a 30lb gas spring). However, during ship night while testing and tuning PID loops one of the gearbox's broke down on us. We had spares of the last plate made for our first regional, but after our first experience didn't feel comfortable with the gearbox's.

So we decided to totally change motors and install a gas spring strong enough to hold all the weight of our arm (90 pounder). This meant we didn't need the torque of the FP anymore and could get away with using on window motor to power the arm. The unexpected advantages of using the window motor is that it made the movement of our arm much smoother and more controllable, plus the advantage of it using a worm gear so no back-driving.

These gearbox's can be useful for some purposes.. but driving the main joint of a FIRST arm is not one of them.