gait

A gait is the repeating pattern that decides which legs move when — the choreography of stepping. Just as a horse can walk, trot, canter, or gallop, a legged robot has several gaits to choose from, and each is simply a fixed order and timing for lifting and planting feet, repeated cycle after cycle. Picking a gait is like picking a dance step: once chosen, the legs take their turns in the same rhythm over and over until the robot decides to switch.

Different gaits trade stability for speed. In a walk, the legs move one at a time so plenty of feet always stay on the ground, keeping the robot steady but slow. In a trot, a four-legged robot moves diagonal pairs of legs together — front-left with back-right, then front-right with back-left — for a quick, balanced jog. In a gallop the legs fire in a fast, sweeping sequence, and the footfalls follow so rapidly that there is a brief instant when no foot is on the ground at all — the fastest gait but the least stable, since the robot is momentarily airborne and must time its landing.

Engineers boil a gait down to a single revealing number: the duty factor, the fraction of each cycle that a given foot spends on the ground. A duty factor above one-half means each foot is down more than half the time, so several feet always overlap on the ground and the robot is solidly supported — a slow, safe walk. A duty factor below one-half means each foot is up more than it is down, leaving moments with too few feet (or none) touching, which only works at speed using momentum — a run or gallop. So the duty factor neatly separates careful walking gaits from fast running ones.