Self Balancing Egg ( Columbus Egg )

thingiverse

This egg always remains upright once you release it. It contains at the bottom a 5/8-inch or 16-millimeter metal bearing ball that shifts its center of gravity close to its broad base. I printed it in its vertical position with material support only from the printing bed (that is, no material support inside the egg). When it finished printing the internal cylinder I paused the printing, dropped the ball in, and added some glue from a hot gun (epoxy or any similar glue should also be fine), then un-paused the printing. When the printing was complete, I cleaned up the bottom with an X-Acto knife and sanding foam sponge to round it out. Then I balanced it by placing it on a flat and smooth surface, observing its orientation and sanding slightly the side of the bottom that was too high (the egg tilts away from the high side). PLA, 0.2 millimeters, material cooling fan on, 30 millimeters per second, support from printing bed only (not inside the egg). If you want to tweak the design or dimensions, load the .scad file and generate the STL using OpenScad (free, open source, runs on all major OS's). I tried to mark it as customizable but Thingiverse timed out too early.