[Greg Needel]

i personally am a big fan of encoders. if you put an encoder on the motor driving the arm, or any other rotating shaft in the system; you can figure out the set number of rotations from start to your limit. I think this works well because at any given time you can change the location of your stop just by changing the number of rotations. You will still need a limit switch at the bottom of your arm movement to act as a "zero switch" so that the system re-calibrates itself when it comes in. Another advantage to this is you can make buttons that go to exact positions on the arm. since you know the number of rotations at any given height you could make a "center goal" button and not have to drive the arm manually to get there.