Some friends of mine visited Mali and brought back a baliphone as a present. These are marimba-like musical instruments constructed from wood and calabash gourds and played with mallets.
I thought it would be fun to build a programmable mechanical baliphone player. It includes a MIDI interface so that the baliphone could also be played using an electronic keyboard.
This was the first time I had worked with rotary solenoids. One difficulty was minimizing the noise that the mallets made when deactivated after striking a note. Foam padding was adequate, but a potentially fruitful area of further exploration is actively controlling the solenoid current as the mallets recover.