Stepper motors commonly used on 3D printers and other CNC machines can be made to hum at specific frequencies. For this instrument we used that possibility to play notes with a droning quality. On the back of the instrument you can see the 4 nema-17 stepper motors. For convenience we used a popular arduino CNC shield on top of an Arduino mega.
back of the instrument
front of the instrument without the fins
Each motor has a birch plywood wheel with cutouts that when in motion generate Moiré patterns.
Some of the initial tests for the wheels involved spirals, here are some of the initial spiral simulations:
https://s3-us-west-2.amazonaws.com/secure.notion-static.com/97a08e3e-2de1-489f-9936-f4c2366e86c3/spirals1.mp4
https://s3-us-west-2.amazonaws.com/secure.notion-static.com/bbe443d1-d61e-4054-839b-74a89d5c1fd8/spirals2.mp4
And we ended up going with a simple wheel and fins design:
https://s3-us-west-2.amazonaws.com/secure.notion-static.com/a8b3a1ef-df92-4f53-9346-27dd0b26b06a/fins.m4v
One of the challenges of using small stepper motors to drive big wheels is that there can be missed steps if the motor can't move the wheel. Our work around was to create flexible joints in order to give the motor some flex on every start. That explains the kerf bending pattern on the center of each wheel:
An added benefit of this configuration is that it increases the noise produced by the instrument as these wheels behave like vibrating strings and the case works as a resonator. Each fin is attached to the stepper motor using a stepper motor flange shaft coupler.
Four of these adafruit nema-17 stepper motors are driven by A4998 stepper motor drivers, these are stacked on an arduino uno CNC shield for convenience and that is connected to an Arduino Mega on top of a prototyping shield (also for convenience). We are using the NRF24 module for wireless communication. Everything is powered though a single 12v 3A power supply. The arduino mega can accept 12V on it's barrel connector and conveniently it can output 3.3v for the wireless module.
