The main problem is scaling the signals. The potentiometer will be something like 0 - 10v, the joystick is in -1 to +1, and you are thinking in terms of angle of the arm. Take a look at the following link:
http://team358.org/files/programming...2009-/LabVIEW/
Towards the bottom is a good Labview example of slaving a Joystick to a potentiometer signal using PID. I think this is similar to what you want to do. Take a look and reply back with more questions.