A hexapod walker called Stewy uses a Stewart platform as its head, with the same 6-DOF servos driving both the platform and the legs. The robot could not sense ground contact, limiting mobility on uneven terrain. Builder JD fixed this for roughly 6 cents per leg.
The method is a resistor in series with each servo motor. Current draw rises with torque, so a voltage drop across the resistor, read by an analog microcontroller input, gives a real-time torque estimate. No strain gauges, no load cells. Just Ohm's law. The signal quality is better than the parts cost suggests, though JD had to reduce servo speed to clean up the data.
The technique is not new, but the implementation details and the signal quality JD demonstrates on video are worth studying. The original also covers where this approach breaks down and points toward purpose-built force-sensitive resistors as an alternative path, which have appeared in applications from MIDI controllers to self-leveling 3D printers.
[READ ORIGINAL →]