[Travis Schuh]

We are also very concerned about backlash on our arms. This year we achieved some pretty good backlash performance. We used a large chain reduction for our first reduction, and then on the first shaft we made a custom shaft where we sized the hex shaft as a press for the sprocket on it and the gear for the next reduction. The Vex Pro hex in their hex broaches gives a lot of wobble, I think we sized it at .507 for the light press, a big difference from the .500 undersized hex they sell. We use #35 chain because not only would we be on the edge of #25's strength, but #35 chain is much stiffer than #25. This isn't backlash, but does impact the dynamic stiffness of the arm system. A classic example is looking at 968's arm in 2005 compared to 254's that year. 968 ran #25 and was in spec, but it added a low natural frequency to the system that was apparent when the arm stopped. 254 ran #35 and didn't have this problem. Another thing we do is our encoder is mounted via MXL timing belt off of the chain reduction shaft so that what little backlash we have is practically all behind our encoder.