[ZZII 527]

Originally Posted by AdamHeard

Last night we experienced a weird failure on our arm while we were tuning a PID loop.

We have two 42mm 256:1s on our shoulder joint with further reduction after that. One Fischer price and one banebots.

We were tuning, and therefore some oscillation of the arm was unavoidable.

After some test, we found the arm couldn't move. At all. We removed the chain and found the BB gearbox could spin, the FP one was jammed. We disassembled both and looked inside. The BB was fine, the FP however had sheared about 1/3- 1/2 of the teeth off each of the brass planetary gears in the final stage and had jammed shut. We replaced the damaged gears (The sun and carrier were fine), closed it up and it worked.

What was interesting about all this is that the Double-D joint was fine in both boxes, and had no more backlash than our untouched gearbox.

We found that the BB motor PWM had become loose, so we never gave current to the motor, and therefore were putting to much strain on the FP gearbox. This is just a guess, any insight would be appreciated as we hope this does not ruin this season if it has the potential to reoccur.

The only thing I can think of (other than what you said about backdriving the BB with the FP) is something that happened to our 42mm gearbox: The four long screws that hold it together came loose little by little until eventually the entire housing would twist under the torque from the motor. This would not occur if you are using the holes on the sides of both bearing plates to mount the motor, but we are only using the front face of one bearing plate. Luckily, we spotted this before it became a problem, but I imagine it would really mess with the alignment of the gears and could cause them to bind. The simple solution is to Loctite them and tighten a lot.

Glad to hear that your carriers are holding up, though. Team that are using the 42mm with FP as speed sources with a lot of extra reduction should be okay.