That's exactly how the arm on Storm II works, it uses a 10k Pot mounted inside the gearbox block that drives the arm mechanism to relay end-stop (not position) information to the speed controllers. We avoided creating a 'giant servo' approach where the arm would fight to stay in whichever position we wanted it in for fear that in a fight that's just not practical, something jams the arm and you're looking at a stalled out motor with very little you can do about it.

Can't tell you enough how you do NOT want to run that as a giant positional servo