We have a shoulder and elbow as well, with a gusset that reduces our required torque by about 45% and latex tubing providing 'neutral buoyancy' so that our 64:1 BB has to exert very little force to lift the arm. (I can do it easily with one finger, and I have both carpal tunnel and tendinitis!)
http://www.youtube.com/watch?v=FUNFcvnKQ-Q
It doesn't backdrive at all.