Alec Smecher assembled this project that produces synthesizer sounds with spinning speakers attached to a motor controller operated by a toy guitar:
Motor controllers and their matching motors make neat (often octave-ish) noises. In essence, a motor driver is a synthesizer of sorts.
Motor drivers are basically the same as amplifiers.
Plastic toy guitars are often horrible anti-instruments and need rehabilitation.
I’ve always had a soft spot for the Leslie speaker.
He walks through the build process in the first part, with the spinny sounds bits beginning around 3:45:
Awesome. Simply awesome. BoM and build notes here at cassettepunk.