A Robot Plays Music by Automatically Twanging Four Rulers
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.
They've automated the classroom trick of twanging rulers—and multiplied it by four. Bring this to school and you might get scolded by four teachers at the same time.