Built this about 10 years ago. It came back a few years after that for new rubber bands and shrink wrap tubing :) when I took this video of it in operation. I only recently found it (this morning).. was a fun project, thought I'd share it. All pneumatic, no electronics -- and pretty low-budget! Uses 3 air cylinders, one valve (5/2?), and air limit switches. And rubber bands, of course!