I played around with cardboard, tape, glue and marbles a lot as a kid, making tracks and ramps and such just for fun.
I had been wanting to make one of these for years, just to see what I could come up with now that I'm a little older. The main thing I'd been wondering about was how I could get the marbles back to the top with some sort of mechanism made from simple, available items.
The whole thing turned out pretty well, and surprisingly, the motor/conveyor belt system I came up with works perfectly, although the initial version was really fast (see the video in step 6).
I made a few changes to slow down the conveyor, and the final painted version is shown here.
Step 1: Supplies
I used lots hot glue, along with some wood glue and white glue in a few places.