Rattleback

Edit: I had some trouble with this originally and VeryWetPaint was nice enough to fix some things and uploaded a derivative. I didn't want to leave this half finished though so now that I've printed and tested, I'm updating with new models and the original Inventor files. If I get a chance I may try to figure out how to model this in Openscad.

A fun and confusing toy that will rotate freely in one directly, but when spun the opposite direction will stop, wobble, and reverse directions.

More on wikipedia: http://en.wikipedia.org/wiki/Rattleback

Uploaded at the request of Spacexula