The effect of leg compliance in multi-directional jumping of a flea-inspired mechanism

Inspired by the relationship between leg compliance and jumping performance in the false stick insect, this paper describes how variations in leg compliance and jumping direction affect the performance of a flea-inspired jumping mechanism. The amount of energy lost during jumping was determined by examining the ratio of kinetic energy to input energy (also called conversion efficiency). Leg compliance is modeled based on the compliant mechanics to determine energy transfer during jumping and determined the optimum degree of leg compliance for maximizing performance. Jumping experiments are then performed using six different legs with progressively greater degrees of stiffness and three different jumping directions. The experiments show that conversion efficiency decreases by approximately 3-5% as leg stiffness increases, compared to the optimal case. In the most compliant legs (i.e. stiffness of 0.0338 Nm rad^-1 or less), conversion efficiency rapidly drops to near 0% because the leg bends so much that it cannot support the thrusting force. The optimal conversion efficiency tends to increase when the mechanism jumps vertically owing to reduced slippage and increased ground reaction force. These investigations show that optimizing leg compliance can improve the performance of a jumping robot by up to 5% by enabling more of the initially stored energy in the leg to be used. This finding will likely prove helpful for choosing the leg stiffness for a small-scale jumping robot.