I found this tremoloa instrument in a dumpster near my house. I gave it a second life.

 

Automated Tremoloa.

I found this tremoloa by the dumpster, so I took it home and automated it. Everything is currently controlled by an Arduino Nano. The aluminum frame was made from stock material from Home Depot, and the acrylic parts were designed in Fusion 360, then cut with a laser. The chords are played by solenoids, controlled by a relay module. The stepper motor for the plucker is a nema 11 and the drive rail is a nema 17. Position of the rail and plucker are calibrated with limiter switches.

An Arduino Nano is the brains of the project.
The Arduino Nano sits on top of two motor controllers with large heat sinks. One controller the stepper motor to move the plucker along it's rail, the other controller the motor on the that did the plucking.
The chords were struck by small solenoids, controlled by relays.
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An early iteration of the plucking device, laser cut from acrylic. The cheap stepper motor was replaced with a better one and a limiter switch was added to confirm if a full plucking motion had been completed.
The solenoids used to strike the chord strings.
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