This coming semester, I've volunteered again to teach a robotics course at the local high school. The class of 20 students will be studying CAD and programming, beginning with ActivityBot programming in Spin. I will have 10 students on Tuesdays for an hour and a half, and the alternate ten on Thursdays for the same amount of time.
The course objective this semester is to design and program a robot arm capable of solving the Towers of Hanoi problem. (Thanks, erco, for the idea!) The CAD side will design the mechanical parts in Rhino, to be cut out on the school's laser cutter. The programmers will have to learn how to control the robot and figure out the puzzle algorithm.
I've never built or programmed a robot arm before. In order to stay a step or two ahead of the kids, I needed to do that -- pronto! So I went online and found a laser-cuttable arm design (the uArm
) that uses standard servos and is free to duplicate under a Creative Commons license. In order accommodate the cheap 2.7mm meranti doorskin that I wanted to use, my own bearings and bushings, the Activity Board, and my own gripper design, I needed to make a considerable number of mods to the uArm patterns. Here's a short video of the result:
I like the uArm design, since it incorporates parallelograms that keep the gripper relatively level. That way a lot can be done without needing a wrist motor. It also has the advantage of keeping all three motion servos affixed to the base, so the arm does not have to lift them.
The video demos my first program, and the motions were sketched in totally by trial and error. I need to do a thorough kinematics and reverse-kinematics analysis yet, in order to produce predictable results. I'm thinking of redesigning some of the parts to incorporate protractor elements on the joints. That would make it easier to calibrate in terms of pulse-width vs. arm angle.
Anyway, I'm hoping to get the Towers of Hanoi program operating in time for the first class day. I can then invite a volunteer to try to beat the robot, using a separate of set of spindles and disks.
Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery