08-17-2017, 12:08 AM
Hydraulic arm - use syringes, aquarium tubing, wood. Kids build a similar one at a 4H junk drawer robotics class and love it. Pencil top erasers at the end of the hand work well as grippers. Let them try it first with air in the lines instead of water - air compresses so it doesn't work as well. (Good to teach some about properties of liquids, solids, gasses.)
Mechanical Arm
Here's a mechanical arm I built for a class this semester. It uses syringes and rubber tubing to act as a hydraulic system. For the most part syringes work nicely, but filling them up so there's no trapped air is a pain. Since water is practically incompressible, the syringe plungers should move equally because both syringes are the same diameter. I should have changed the gripper syringe's diameter so its plunger had less movement but more power. Currently, half of its length is unused.
Hydraulic Animation
The general idea.
We had three weeks to design and build it, and then we were supposed to have a contest to see who could stack six wooden cubes into a pyramid the fastest. The contest never really materialized although I think mine would have come in second. A lot of other people's arms didn't really have much range of motion or were awkward to use.
I set my syringes up to act as first class levers while everyone else used a third class lever setup. Both have the same power, but I think it was easier to adjust mine to get a good range of motion. Our arms were required to have four degrees of freedom. Mine swivels at the base, moves at the shoulder and elbow, and has a gripper that's way too complicated.
The gripper has a total vertical displacement of 27 inches. It can reach 5 inches below its base, and a maximum of 22 inches above. The whole arm can rotate through about 35 degrees which is pretty good compared to my classmates.
