Robotic vertical jumping agility via Series-Elastic power modulation

Several arborealmammals have the ability to rapidly and repeatedly jump vertical distances of 2m, starting from rest. We characterize this performance by ametric we call vertical jumping agility. Through basic kinetic relations, we show that this agility metric is fundamentally constrained by available actuator power. Although rapid high jumping is an important performance characteristic, the ability to control forces during stance also appears critical for sophisticated behaviors. The animalwith the highest vertical jumping agility, the galago (Galago senegalensis), is known to use a powermodulating strategy to obtain higher peak power than that of muscle alone. Few previous robots have used serieselastic power modulation (achieved by combining series-elastic actuation with variable mechanical advantage), and because of motor power limits, the best current robot has a vertical jumping agility of only 55% of a galago. Through use of a specialized leg mechanism designed to enhance power modulation, we constructed a jumping robot that achieved 78% of the vertical jumping agility of a galago. Agile robots can explore venues of locomotion that were not previously attainable. We demonstrate this with a wall jump, where the robot leaps from the floor to a wall and then springs off thewall to reach a net height that is greater than that accessible by a single jump.Our results show that series-elastic power modulation is an actuation strategy that enables a clade of vertically agile robots.