XA10C4's Ruler Drive turns the familiar trick of twanging a ruler over the edge of a desk into a four-voice automated instrument. Stepper motors change each ruler's effective length to set its pitch, while solenoids strike the rulers; the machine is controlled over MIDI and the published demo performs the notoriously fast piece Rush E.

Built from an aluminum frame and 3D-printed parts, it mechanizes a very simple school-desk noisemaker into a programmable musical robot.