Hey thanks a lot for all the input. I forgot to turn on email notifications and was a bit surprised that I did not get any reply. lol.
Please look at the attached images for an explanation of what I want to do. Never mind the marbles, but for size comparison note that they are of a bigger size than the standard marbles. 
It is a toy piano with metal bars/staves/rods whatever you would call them, but not strings. I guess I should have been more clear with that.
I am not out for making it playable by midi in any ordinary sense, I am more out for creating som experimental textures or motions.
Multiple solenoids could work I guess but it would be very expensive since it is something like 12 rods.
I think that that leaves me with a pulley that is connected to either a DC motor, stepping motor, or a servo. Stepping motor seems to be the best.
Please look at the sketch to see my idea for a hammer. For lifting to skip notes, maybe a solenoid would work?
How fast can a stepping motor go?
