The drives make sounds mecahnically by electrically pulsing the motor at any number of positions to generate different frequencies (and different notes). For this reason, I've narrowed down my classification choice so far to "52. Electromechanical instruments and devices" which MIMO says are:
"Configurations of (electrically excited) silent, mechanical moving parts with encoded patterns, and electronic circuitry. The movement enables the encoded patterns to be transduced into an analogue fluctuation of an electric current"
Which makes sense to me.
They subdivide this into "Tone wheel instruments", "Photoelectric electromechanical instruments", "Record/playback devices", "Electromechanical samplers", and "Electromechnical sound processing devices". Having read through all of these and their examples, I feel like musical floppy drives are closest to tone wheel instruments such as the Telharmonium, but I am definitely not an expert on the subject.
Hopefully this is the right place to ask this, but is there a better classification in the Hornbostel-Sachs system? Or is this classification correct?
Thanks so much!