Computational design of wind-up toys.

Wind-up toys are mechanical assemblies that perform intriguing motions driven by a simple spring motor. Due to the limited motor force and small body size, wind-up toys often employ higher pair joints of less frictional contacts and connector parts of nontrivial shapes to transfer motions. These unique characteristics make them hard to design and fabricate as compared to other automata. This paper presents a computational system to aid the design of wind-up toys, focusing on constructing a compact internal wind-up mechanism to realize user-requested part motions. Our key contributions include an analytical modeling of a wide variety of elemental mechanisms found in common wind-up toys, including their geometry and kinematics, conceptual design of wind-up mechanisms by computing motion transfer trees to realize the requested part motions, automatic construction of wind-up mechanisms by connecting multiple elemental mechanisms, and an optimization on the part and joint geometry with an objective of compacting the mechanism, reducing its weight, and avoiding collision. We use our system to design wind-up toys of various forms, fabricate a number of them using 3D printing, and show the functionality of various results.