“Remix of Marble Caster by HipsterLogic (http://www.thingiverse.com/thing:8959/) Designed for a 5/8” ball bearing (http://www.mcmaster.com/#96455k58/=z8321g), which operates smoother than the marble. Full drawing robot project documented at http://www.instructables.com/id/Low-Cost-Arduino-Compatible-Drawing-Robot/”