Gait Cycle and Duty Factor

The gait cycle is one full stride from touchdown to the next touchdown; the duty factor is the fraction spent on the ground.

The gait cycle, or stride, is the complete cycle of a single foot from one touchdown to the next, split into a stance phase (foot on the ground, bearing weight and propelling) and a swing phase (foot lifted and moving forward). The duty factor β = stance time ÷ cycle time. Biomechanics commonly uses 50% as the dividing line: a duty factor above 50% counts as walking, where at least one foot is always on the ground; below 50% counts as running, which includes an aerial phase. For quadruped and humanoid robots, a periodic gait can be described with three quantities: the cycle period, each leg's duty factor, and the phase offsets between legs — a diagonal trot, for instance, has the two diagonal leg pairs offset by half a cycle. Model-based controllers use these quantities to schedule when each leg touches down (gait scheduling), and reinforcement-learning locomotion controllers often feed a phase clock into the observation or reward to guide the policy toward a desired rhythm.

ExampleA leg with a 0.5 s cycle that spends 0.3 s on the ground has a duty factor of 0.6, above 0.5, so it counts as walking; if it only touches down for 0.2 s, the duty factor is 0.4, and there's an aerial phase — that's running.

Also called

Stride, Duty Factor

Related

Gait · Stance Phase / Swing Phase · Trot Gait · Gait Planning · Gait Phase (Phase Clock) · Flight Phase (Aerial Phase)

Sources

Wikipedia: Gait