[JesseK]

CAD a gearbox with a clutch in it. Source the clutch, try to find a sketch or detailed drawing for it, and put it into the gearbox.

Clutches act as good mechanical safeties for the very likely event your programmers muck something up during the course of sensor software integration. You mostly likely can counter-balance your lift or arm so the clutch isn't always slipping; conversely if the arm/lift gets caught on something then the clutch will slip. The caveat to this approach is that your rotary sensor (potentiometer, encoder) will need to be mounted after the clutch rather than before it -- i.e. you should put it on the rotary joint itself rather than the 1st-2nd stage of the gearbox.