We just finished assembling our replacement arm. It uses a van door motor driving an 8 inch diameter pulley to increase the torque and slow down the motion so that the limit switches have time to act. In the video, the limit switches are actually wired in series with the motor so that they cut off the power to the motor at the appropriate time. We used some 3mm Dyneema cord wrapped around the motor shaft and the pulley. We found some "non-traditional" material to make the body of the arm out of. It has more than adequate stiffness, was easy to work and has a low coefficient of friction.
http://www.youtube.com/watch?v=auKJTV7fTj4
We will see how well it works tomorrow at Lone Star.