I didn't have any particular design in mind, so I designed it as I built it. Being so small at only 4" square, there wasn't much room for many varied tracks for the ball bearings, so I eventually settled on the design of the letters USB as the tracks. The ball bearings are about 4mm taken from an old dead bicycle hub, it probably work better with more ball bearings, but I haven't got any yet. The Marble machine has a USB port on the front which which can be handy,
- Plywood 12mm and 18mm, about a foot square of each should plenty.
- Ball bearings, around 4mm
- An old VCR read head, with bearings in good order
- A small DC motor from a CD drive or similar
- 6 - 8 diodes, any will do
- Small slide switch S.P.S.T fine
- Wood screws 1"
- Epoxy (5 minute cheap stuff fine)
- Thin clear plastic, from drinks bottle or craft store
- USB cable with male connector
- USB cable with female connector
Warning: I am not an expert in electronics (in case you didn't notice from my dire soldering), if you blow your USB port up, your computer, your house or your cat, it's not my fault! Proceed with caution!