Good ideas about hitting the rod (it is not strings) in an alternate way. Slapping is a one of the solid ways I think. The vibration idea is nice, and would produce a unique sound! I still need to figure out how to move between rods.
That is some really cool projects Mike!
I am curious on how fast those solenoids can work, like if they can hit again before they are retracted fully. Reason is, I am out for artificial (and good) sounding playing, maybe a bit Nancarrow-like, if you are familiar with his music. Thinking a bit more now, if each of the 13 rods is hit by the solenoids with 10 ms in between, the first solenoid would get 130 ms to get ready.