Our percussion bot uses two motors as actuators in an unusual manner on top of a commercially available cajon. Here is a short explanation :
The idea came from watching Donald Bell's experiments using the same method here and here. According to him (in personal communication) this was an idea by Moritz Simon Geist(on IG).
The advantages of using motors in this fashion instead of solenoids is that they have a less "clicky" character and the expressiveness can be adjusted by varying the pulse lengths in software (or on/off timing) and mechanically by changing the spring's tension or the stopping points.
The microcontroller on this one is a Teensy 2.0 driving the motors through the trusty IRLB8721 N-channel power MOSFET in a configuration very much like this one (here is a comprehensive tutorial):
