Quote:
Originally Posted by dmitch
Our team's arm has an elbow joint and a shoulder joint just like an actual arm. Does anybody else have this design? Only problem with ours is that if it is fully extended there is too much torque so we have to be careful of that or else we will break the arm  |
Yup, and those are the exact terms we use. We were very careful to put the weight of motors, et. al., close to the shoulder joint, we minimized the torque we'd put on the shoulder when at full extension. We have a custom-made worm gear on the shoulder to act as our anti-backdrive (shoulder powered by two BaneBot 775's through a CIMple Box, through the worm gear), and when the arm is fully extended we broke teeth (from a cast-iron worm gear) when we stopped the arm quickly. Our elbow is driven by a FP motor mated to a yellow DeWalt drill motor (to give us anti-backdrive there), with one intermediate stage to slow down the rotation rate of the elbow.
We reduced the amount of work the shoulder had to do by adding counter-force on the shoulder pivot. We got some rope, pulleys, and springs from Home Depot and connected the springs to the arm on the back of the pivot - that means instead of adding to gravity and momentum, we actually have to POWER the arm down (which makes it much smoother). On the up-swing, we're powering against gravity, but also getting help from the springs. We are also adding ramping code so that we don't "suddenly" start and stop motors to prevent damage to the worm gears.
EDIT: You can see two of the springs just above our bumpers on the left side (another set is on the other side), and follow the white rope up to the back of the main arm (they're held by loops attached to the box aluminum on he back of the main arm).
-Danny