Stewy is a very interesting robot, with some slightly odd kinematics. Its head is a Stewart platform, which is a common-enough 6-DOF actuated plate normally used with a fixed base. By connecting legs to the same servos running the Stewart platform, [JD] turned it into an adorable hexapod walker. The walker had a problem, though: it can’t feel its feet, and [JD] thinks that would make it much more mobile on uneven surfaces. So he got some resistors to turn the cheap servos in its legs into force-sensing actuators.
Well, almost. He’s not actually putting strain gauges or anything like that into the legs; he’s just measuring the voltage drop across a resistor in series with the servos. Since the motors draw more current the more torque they’re putting out, he has a very quick and easy way to sense the current and thus the torque using good old Ohm’s law and an analog input on the microcontroller driving the robot. It’s a simple hack, but the data he’s getting is surprisingly good for how much work it is to add to a robot, as you can see in the video — at least once he slowed down the servos a touch.
Perhaps this isn’t a ground-breaking innovation, but [JD] does a very good idea explaining it. Of course if you want to use resistors to sense force directly, force-sensitive resistors are a thing that we’ve seen in everything from Twister-mat MIDI controllers to self-leveling 3D printers.
