You don't necessarily have to rotate the joint of the arm to get the arm to rotate. You could use a lead screw/cable to pull/push somewhere on the arm. There a lot less torque involved if you do it this way.
If you're interested in 254's 2010 climber, they have pictures on their build blog.
It looks like the teeth on one of the sprockets are a little broken.
I'm having trouble linking to the pictures, so here's a picture uploading to google docs.
https://drive.google.com/file/d/0Bzf...it?usp=sharing