Actual Arm

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 :smiley:

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).


We used pneumatics, not worried about backdriving or breakage. The double piston gives us three positions and our forearm makes up the difference.
(our “forearm” is short and driven at 3:1 with a window motor)

That is exactly like our arm too. Except we typically refer to it as a wrist and shoulder instead of elbow and shoulder. We ended up using a CIM-U-LATOR gearbox tied to a GEM 500 gearbox to get enough torque for our arm. When we started it in testing we imediatly started breaking chain left and right. It was crazy, but then we found a really nice system for hooking turnbuckles into the chain directly by using master links. This fixed the connection points in our chain, and it hasn’t broken since. Here is a video of everything working:

We did the same thing. We used two denso window motors with a gear reduction system for the first joint. Then we used an eight inch stroke piston for the second joint and a six inch stroke piston for the claw. As you can kind of see in the photos. It works great for us, we can pick tubes up off the ground without any problems and place them on any of the racks.

We have a shoulder and elbow as well, with a gusset that reduces our required torque by about 45% and latex tubing providing ‘neutral buoyancy’ so that our 64:1 BB has to exert very little force to lift the arm. (I can do it easily with one finger, and I have both carpal tunnel and tendinitis!)

It doesn’t backdrive at all.

we made our “arm” an actual arm. it has a should joint, elbow joint, wrist joint, and a hand(claw). It works great but the shoulder joint dosent work to well

Ours is also an arm with three sections: the long one, the short one, and the gripper :smiley: (with Points Of Articulation #1,#2, and #3 down the arm). We seemed to have the torque issue fixed with an adjustable spring and pulley system, and then the chaining started pulling our window motors apart due to the forces involved in braking the arm during a fall :eek:. Hopefully we’ll be able to resolve that issue and actually make a gripper by competition (the one I had made was much too heavy, 5.5 ibs at the end of a 4ish foot arm).

Subtract 1000 from the team number of the original poster and you get 997. We also did an arm with a shoulder and an elbow. Producing enough torque was definitely an issue, especially with the weight of our gripper. A series of belts and pulleys has solved our issues.