Here's my story for the past two days. Pretty much I have spent all my waking hours (outside of class) trying to get our arm design to work. We have a 5 foot upright (made of 2" square aluminum tubing) with our swinging arm made from two pieces of 80/20 extruded aluminum (one piece slides to increase length with the help of a piston), and then our whole gripper/grabber assembly on the end of that. The whole swinging arm weighs around 4 pounds. To power this we are using a single Fisher Price motor with the stock gearbox. We modified it a little so that our output is now a 1/2" keyed shaft.
At first, we tried using some 1/4" timing belt with pulleys we ordered from McMaster Carr, but there wasn't enough engagement and the belts would slip. So we quickly rigged up some chains and sprockets (with the same reduction) to see if we'd have enough torque. The arm moved with ease, but the setup was a bit messy (sprockets cockeyed, chains too long/short etc.) and the Victor would trip if we put more than about 20% power to it.
So, we cleaned up the setup a bit, and it looks pretty nice now, and still moves the arm with ease (extended and retracted). I will try and get some pictures, unfortunately the only reference I can provide is this little pic I painted for your viewing pleasure. Slapping that tetra on there though puts about another negative 40 or so foot-pounds for us to work against and trips the Victors and releases a little magic smoke.
So we concluded we are going to have either make our own transmission, use a different motor, or both. Right now, we are thinking about perhaps putting the globe motor on the FP transmission, or maybe using two FP's in tandem. We would like two arms though so our goal is to save the other FP if it works; we'd definitely rather have one versatile arm over two of what we have now though.
Anyway, anyone have any idea why we are stalling it and tripping the Victors? The way we calculated we should have more than enough torque but oh well
It's about a $50 (so far lol) setback that we don't really want to make bigger.