A Passive, Origami-Inspired, Continuously Variable Transmission

Transmissions play a vital role in machines by transforming the torque and speed of a motor into a desired output. They are often necessary for operating a motor at peak efficiency or power. The majority of variable transmissions are mechanically complex, large, and expensive, which limits scalability and is often cost prohibitive. As an alternative, we propose an origami-wheel design that is capable of varying its own transmission ratio between motor torque and ground reaction force, effectively creating a passive, continuously variable transmission. The wheel responds to an increase in torque by reducing its radius through the spring-like properties of the origami structure, increasing the force applied by the wheel to the ground. We demonstrate that the wheel is able to match the speed of a 55 mm fixed-radius wheel when unloaded, and can also tow loads as high as a 25 mm wheel without stalling. This design could be used to provide smaller, cheaper robots with an effective means to vary their output while maintaining motor efficiency.