If you have a laser machine collecting dust because you have nothing inspirational to cut you are in luck. This Laser Cut Hand Crank Marble Machine by Martin Raynsford is the final version after a ton of experimentation. It looks like it is lots of fun and would be simple to stick a motor on the shaft that is normally turned by hand.
“The main feature of this marble machine is the ring lift. Three stacked pieces of wood mean that the holes the balls are sat in are actually sloped. When the ball enters at the bottom it wants to stay inside the ring, as the ring is flipped upside down the slope is reversed and it wants to push the ball out of the ring. The balls then run down a 5 loop spiral and back into the bottom of the machine ready to go again. The machine holds 6 balls comfortably but a few more could be held in the lift at any given moment.”