There is going to be a pull-type 12V solenoid at the end of each arm that will trigger the drum stick by pulling its end up, so it comes down and strikes the drum. The spring on the other end will pull the drum stick back up after a strike.

I tried relays, but since the music is Drum and Bass, the High Hat will be getting a barrage of 16th notes at high tempos, so I went with MOSFETs. I got a few different solenoids, but this medium sized one from McMaster Carr seems to be a good fit for striking most drums. The heavier solenoids might work best for pedals.