I know I have some better close up pictures at home, PM me your e-mail address if you'd like them. This is from our Overdrive robot:
http://www.chiefdelphi.com/media/photos/30270
http://www.chiefdelphi.com/media/photos/30267
The whole thing is pretty straight forward:
- Each stage fits inside of another stage, loose enough that it doesn't bind, but tight enough that it doesn't wiggle loose.
- At specific points, there are brackets that hold small wheels on (you can see one of the wheels at the top of the first picture) in order to hold the whole thing together. The outer most stationary section has the wheels bolted to the top, and the middle section fits inside of those wheels. Then the middle section has wheels bolted to the bottom that wrap around the outer section. As you pull the middle section up, the wheels get closer together. As you can imagine, this means there's more stability when it's all the way down, versus all the way up... but still stable enough for our purposes.
- We used a big drum at the bottom, powered by a motor, to lift the arm, and allowed gravity to lower it as we ran the drum in reverse. The cable routing went from the drum to a fixed pulley at the top, down to a pulley attached to the bottom of the middle stage, up to a fixed pulley at the top of the middle stage, and finally down to terminate at the bottom of the inner stage. If required, you could run a cable opposite this one on the same drum to pull it down.