Gear Backlash in Robot Joints

Most robot joints are driven by a fast small motor through a gear reduction, and the position controller almost always reads only the motor's own encoder — cheaper than adding a second sensor on the output side. This simulator models the small dead-zone between gear teeth (backlash) that sits invisibly between those two encoders: a real single-link joint swings under a PID controller that thinks it is tracking perfectly while the output link lags, drifts under gravity, or — with aggressive gains and a wide gap — falls into a visible limit-cycle chatter as it repeatedly crosses the dead zone and slams the opposite tooth face. Adjust the backlash gap, gear ratio and PID gains and watch the "gap consumed" and tracking-error readouts reveal exactly how much of the joint's real motion the motor-side controller can never see.