Rattleback

thingiverse

This ancient curiosity spins one way easily, but refuses to spin the other way! Watch it instead rattle and start to spin back the other way! (Before I realized that the key to getting jaysay's excellent design to work was a gentle sanding, I spent a week designing my own. The original still works better than this one, nevertheless, I thought I'd share.) Instructions To prepare: Print. (I've oriented it at a 45 degree angle to maximize printable space.) Gently sand the bottom of the curved surface especially near the center. It doesn't have to be entirely smooth, just smoother than fresh off the printer. To use: Place on smooth, flat surface curved side down. Flick one end to make it spin. Watch closely. Does it keep spinning? Flick it the other way. Watch closely. How is its movement in this direction different? Observe the shape to figure out why!