Make it swing: Fabricating personalized roly-poly toys

A roly-poly toy is considered as one of the oldest toys in history. People, both young and old, are fascinated by its unique ability to right itself when pushed over. There exist different kinds of roly-poly toys with various shapes. Most of them share a similar bottom which is a hollow hemisphere with a weight inside. However, it is not an easy task to make an arbitrary model to swing like a roly-poly due to the delicate equilibrium condition between the center of mass of the roly-poly toy and the shape of the hemisphere. In this paper, we present a computer-aided method to help casual users design a personalized roly-poly toy and fabricate it through 3D printing with reduced material usage and sufficient stability. The effectiveness of our method is validated on various models. Our method provides a novel easy-to-use means to design an arbitrary roly-poly toy with an ordinary 3D printing machine, extricating amateurs from the dilemma of finding extra weight to balance the shape.