Introduction and Brief Description

The Krakuri “Ready to Fly” penguin is a mechanism that has one degree of freedom. The clockwise rotation of the input crank causes a nautilus gear to turn. Since the shape of the gear changes nonlinearly with respect to theta, it causes a slider inside the mechanism to move up and down. The slider in turn moves the penguin body up and down. Finally, the wings are pinned to the stationary frame, and the vertical movement of the penguin causes the wings to flap up and down. 

Krakuri Book. Pg. 22

The interesting behavior of the penguin is seen in the nautilus gear. Unlike typical spur or helical gears, the nautilus gear changes radius as a function of its rotation. This allows the penguin to have a sort of exciting motion as it bops up and down.