I printed @mroek's Cyclone triple track marble machine and loved it. However, being rather lazy I wanted an easier way to operate the marble lift. So I replaced the drive cap with my own that has a Phillips' indentation at the top, thus allowing a Lego Mindstorms motor to drive it with ease.
mroek's Cyclone triple track marble machine:
http://www.thingiverse.com/thing:1340784
*** IMPORTANT ***
Because the original STL for the marble machine was too large to print using my Dreamer, I printed the marble machine at 90% scale. Therefore, this cap will ONLY fit a 90% scaled machine! You could try scaling this cap UP to 111% which might then fit the original scaled machine.
Here's my video of it in action:
https://www.youtube.com/watch?v=pgCtHhMcmp8