In this video i show how to use an electromagnet with an optical sensor to continuously accelerate ferromagnetic / magnetic spheres around a circular track.

A 12V LiPo battery supplies power to a driver board that energizes a 300turn coil when a sphere approaches, causing it to accelerate into the center of the coil. I've successfully run the device with up to 3 spheres at a time.

The electromagnet is far more powerful against a magnetic sphere, but much more erratic and unpredictable, and the sphere tends to stop suddenly after a few rotations.

STL files:
https://www.thingiverse.com/thing:491...

Music:
Kevin MacLeod George Street Shuffle
Heatley Bros Dimension Drift