Snapping Helical Legs Let a Palm-Sized Robot Hop, Flip, Climb and Swim

A UCLA and University of Michigan team built a 98.2-gram, 11-cm robot whose rear Nitinol legs slowly wind into a helix and then snap, releasing elastic energy far faster than the servos could move the limb. It reaches 3.21 body lengths per second on wood versus 0.79 for a rigid version, and the same snaps act as paddle strokes in water.

• Robot weighs 98.2 g, measures 11×8×4 cm and runs on a 7.4-volt LiPo pack
• Top speed on wood is 3.21 body lengths per second; average across six surfaces is 2.46
• A rigid-legged version reaches only 0.79 body lengths per second and stalls on cloth and grass
• In water the snaps form paddle strokes propelling it at nearly half a body length per second