[JimGRobot]

We had similar problems with our arm, and the main problem is that gravity makes this really two control problems, and one controller can't be tuned to do both well.

When the arm is moving up, gravity turns it into a self-regulating process, which is easy to control with straight proportional. When the arm is moving down, gravity turns it into a runaway process, which is harder to control. We ended up measuring the speed of the arm when moving down, and controlled it that way.

Jim