Bow Leg Hopper

The Bow Leg hopper is a novel locomotor design with a highly resilient leg that resembles an archer’s bow. During flight, a “thrust” actuator adds elastic energy to the leg, which is automatically released during stance to control hopping height. Lateral motion is controlled by directing the leg angle at touchdown, which determines the angle of takeoff or reflection. The leg pivots freely on a hip bearing, and is automatically decoupled from the leg-angle positioner during stance to preclude hip torques that would disturb body attitude. Upright attitude is maintained without active control by allowing the body to “hang” from the hip joint. Preliminary experiments with a planar prototype have demonstrated impressive performance (hopping heights of 50 cm or more), high efficiency (recovers over 70% of the energy from one hop to the next) and low power requirements (45 minutes of operation on a small battery pack).

Our immediate goal is to develop a self-contained, 3D hopper that can be driven by radio control. Engineering challenges include:

• Design and fabrication of the leg and two-axis, actuated hip;
• Development of energy-input (“thrust”) mechanism that is sufficiently fast for normal hopping frequencies (1-5 Hz);
• Sensing and control of body attitude, requiring fine adjustment of the CG/hip relation to generate correcting torques.

The long-term goal is to develop a robot with path-planning capabilities that can accurately step on selected footholds in arbitrarily complex terrains.

A US Patent (#7,270,589) was recently issued for this locomotion concept.