Passive bipedal running.

Human-like running is a natural dynamic mode of a simple mechanical biped. Such a machine consists of two telescoping legs with linear springs, connected by a hip joint with a torsional spring. It will run passively; no pattern of forcing is required to generate the gait. With careful design its energy consumption can approach zero, but in any case the passive cycle can be ‘pumped' by various means to sustain running over a range of speeds and slopes. Passive running can also be realized over a wide range of mechanical design parameters. Some parameter sets produce cycles that are inherently stable; otherwise the mode can be actively stabilized by a simple control law. Thus the passive running model offers an effective foundation for design of practical running machines, and also provides an insight into the physics of human locomotion.