I have a 4-bar linkage arm (or similar design) for a telerobot used in the VEX Robotics Competition. I want to be able to press buttons on my PS3-style controller to have the arm raise to certain angles. I have a potentiometer to measure the 4-bar's angle.
The potentiometer measures the angle of one of the joints in the shoulder of the mechanism, which is similar to this:
What type of control should I use to stabilize the arm at these angles?