Update 5: Machine Assembled, Problem with Worm Gear

So we finished manufacturing all our parts and finally put our machine together. The rack and pinion used to extend the arm works really well. We had to epoxy two racks lengthwise to the arm to make sure it could extend through the entire slot. In order to make sure that this gap would still have the same pitch as the racks (so the gear could run smoothly over them), we used the simple idea of holding the gear over the racks while the epoxy dried, which forced the pitch to be correct. There was also a slight deflection in the gear, but we simply used kevlar string to constrain it in place.

However, we also had a problem constraining the motor that's mounted to the worm gear. While the worm does control the gear for certain angles, Once the arm drops steep enough into the slot the arm's weight is too strong for the couple holding the worm, and the worm deflects back and the gear spins freely. We need to find a way to constrain the worm from deflecting back. The difficulty with this, however, is that we need the worm to be at an exact pressure against the gear. If it's slightly too loose, the worm will deflect back and the arm will fall down. If it's slightly too tight, the gear will bind. We did not account for how difficult it would be to constrain the motors in our original design.

We tried a quick fix of using kevlar string to constrain the motor, but this appears to only work sporadically. If we need a more consistent constraint, we will have to manufacture it.