Impossible stubborn Rattleback - self-reversing

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This is a rattleback, a deceptively simple object with a mind of its own. Spin it one way, and it rotates smoothly. Spin it the other way, and it rattles, wobbles, and mysteriously reverses direction!

 

Tips: If it doesn’t seem to work, try spinning it on a smooth surface or grind with sandpaper visible layer lines.

 

Specs: 11 g, PLA or PETG, 3D printed with variable layer height for perfect balance.

 

Why does it reverse?
The rattleback’s behavior comes from subtle asymmetries in its mass distribution and curvature. When spun in the “wrong” direction, these imbalances generate torque that flips its rotation—turning the seemingly impossible into reality.