Summary

Very impressed by the design of the horses,
http://www.thingiverse.com/thing:584516
I decided to make a simple but reliable setup for the synchronization of the illumination.
The stepper motor could be a geared DC motor as well, depending what you have in stock. However, a geared DC motor gives a more stable view. The motor runs at constant speed. Th the small neodymium magnets trigger a Hall sensor. If your printer is big enough, you could make the rods for the horses a bit longer and rotate them diagonally on the bed. That's why the SCAD file is included. Your magnets have a different size? Just change it in the SCAD file. There you can also change the shaft diameter. The housing (for a stepper motor) is ready for improvement. That was a quick and dirty design, just to get things moving. The cap with moving cylinders is optional.