Bioinspired Jumping Robot with Elastic Actuators and Passive Forelegs

This paper presents a novel approach in determining the best strategy for locomotion in small robots. In particular, jumping rather than walking can been chosen as the more suited gait for micro-robots. When dimensions get smaller, scale effects influence the choice of the best gait, and for relatively high forward velocities, the ratio between kinetic and potential energy makes the gait switch from walking to running. In addition, in unstructured environments a jump can make robot overcome obstacles and uneven terrains. To verify these assumptions, a prototype was developed. The prototype Grillo is a quadruped robot, 50 mm long, that weighs about 8 gr. It has active rear limbs and passive elastic forelegs. The power needed to thrust the somersaults is provided by loaded springs relished at takeoff by a click mechanism. During the flight phase, a tiny pager motor compress the spring for the subsequent jump. In this way, the motor power can be drastically reduced: while the actuator absorbs 0.3 W, rear legs deliver a peak power of about 5 W. When landing, passive compliant forelegs buffer the impact energy, which can be used to empower the robot performances in a continuous gait. In conservative simulations, the robot was able to perform a triggered gait, with a forward speed of 1.5 m/s, which corresponds to about 30 body length s^-1