On: The Lego Great Ball Contraption

[shagie]

At Brickworld, they have workshop modules that are fairly simple to make and get involved with GBC.

For example, the 2022 module - https://youtu.be/AO-5eH7vHTM

https://www.greatballcontraption.com/gbc-instructions

Build four of them and you could run them in a loop.