Sensing servo torque

Whilst playing around with my servo controller I realised that the power used by a servo goes up considerably when it’s under heavy load (such as when it’s pressing against the table and still trying to move). I can, potentially, get an idea of this load by measuring the current that each servo is using and using this feedback somehow. I’ve yet to work out how, but at the very least it could be used to protect the servos against overloading; if the load gets above a certain threshold then stop moving!

Servos with status feedback

I saw these Dynamixel DX servos mentioned on Trossen Robotics this morning, see here. They’re interesting because they have a richer interface than the normal hobby servos that I’ve been looking at and they provide a multidrop RS485 interface so that you can chain multiple servos together and control them individually via a single line. You can get feedback on the angular position, velocity and torque and also alerts if temperature and voltage deviate from expected (user specified) ranges.