Student Josh Sheldon has created an incredible Stepper Motor Organ, a hand-crafted instrument that’s built around 49 back driven stepper motors in order to create a unique synthesized sound. The organ is also comprised of 49 disks, a keyboard with handmade keys, lever arms and finishing keys which were all mounted onto a wooden frame. Amazingly, this build only took about a month to complete.
The operational principle is that when stepper motors are back-driven, they induce a pseudo-sinusoidal alternating current. If this signal is amplified and connected to a speaker, you can listen to it as sound. The pitch of the sound is determined by the frequency of the wave, which depends on how fast the motor is back-driven. Higher speed will be a higher note. I thought this sound was interesting, so I wanted to make an instrument that used this mechanism to make music. This is an experimental instrument I built that uses back-driven stepper motors to synthesize sound.There are 49 stepper motors, one for each note in my four octave instrument. At rest, each motor floats above one of 49 disks, which increase in size exponentially as the notes ascend in pitch. The disks spin together, driven by a single speed-controlled DC motor. When a key is pressed, the corresponding stepper motor is engaged with the corresponding disk in the disk stack, and the disk back-drives the stepper motor.
photo by Josh Sheldon