Hardware & control
Gait
A gait is a recurring pattern of leg motion and contact phases used for legged locomotion. For a biped, it describes how left and right stance, swing, double-support and any flight phases repeat over a cycle; gait is narrower than locomotion, which also includes starts, stops, turns, transitions and recovery.
Also known as: robot gait, legged-robot gait
Updated
A gait organises repeated contacts
ISO 19649:2017 defines gait through the cyclic motion pattern of legs in legged locomotion. A gait cycle provides a reference interval over which contact events and limb motion repeat.
For a walking biped, each foot normally alternates between stance, when it supports load, and swing, when it moves towards the next foothold. Double support occurs when both feet contact the ground. Running commonly introduces a flight phase with neither foot in contact, although exact classifications depend on the motion and model.
Gait is more than a pose sequence
Joint angles show limb shape but do not fully identify how the motion interacts with the ground. The same visible pose path can correspond to different timing, contact force, speed and stability. The MIT walking notes model legged locomotion as hybrid dynamics because continuous motion is interrupted by discrete contact changes and impacts.
Useful gait descriptors include cycle period, cadence, stride length, step width, duty factor, contact sequence and phase. A controller may generate a periodic nominal gait while adjusting foot placement and body motion on every step.
Not every locomotion segment is cyclic
Starting, stopping, sidestepping, turning, climbing and push recovery may transition between patterns or never complete a full cycle. Calling every locomotion trajectory a gait can hide those non-periodic decisions.
Training data should preserve measured contact state, event times, target and actual velocity, terrain, base motion, joint state, contact wrench and intervention or fall labels. If phase labels are inferred rather than measured, the labelling method and uncertainty should be documented.
Sources
Related terms
Hardware & control
Locomotion
Robot locomotion is the process by which a robot transports its body from one place to another through physical interaction with its environment. Robots may walk, roll, crawl, hop, fly, or swim. For a humanoid, locomotion usually means coordinated legged movement such as walking, turning, stepping, climbing, or recovering balance.
Hardware & control
Biped robot
A biped robot is a legged mobile robot that travels using two legs. Biped describes the locomotion structure, not the robot’s overall resemblance to a person: a biped can lack arms or a head, while a robot described as humanoid may use wheels instead of two-legged locomotion.
Data & collection
Trajectory
A trajectory is a time-ordered sequence of states or observations, actions and, where applicable, rewards generated as an agent or robot evolves. A complete episode or policy rollout often yields a trajectory, but the terms are not universally identical: trajectories may be partial, while episodes have dataset- or environment-defined boundaries.
Hardware & control
Support polygon
The support polygon is the convex hull of a robot’s contact areas on a declared support surface. For a biped on level ground it is formed by the loaded parts of one or both feet; it changes when contacts are added, removed or reduced to an edge or toe.
Hardware & control
Centre of pressure
The centre of pressure is the point on a support surface at which the resultant of a distributed contact pressure or ground-reaction force can be represented as acting. In legged robotics it summarises how load is applied through one foot or across coplanar contacts and is commonly estimated from a measured contact wrench.