Jumping Tensegrity Robot Based on Torsionally Pre-Strained SMA Springs

This paper introduces the addition of torsional pre-strain into the manufacturing process of shape memory alloy (SMA) springs to form torsionally pre-strained SMA (TPSMA) springs. These springs have higher performance at the same power input for the same loads and same coil dimensions as regular SMA springs. A modified thermoconstitutive model was presented that can predict the behavior of the actuator based on the amount of torsional pre-strain added into manufacturing process and a simple two-state model is used to predict its actuation stroke. These improved actuators were used in the development of a tensegrity robots capable of fast rolling motions and of jumping both vertically and horizontally. This robot is capable of rolling at 0.14 body length per second (BL/s) and can jump up to nearly a full body length.