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.
Also known as: bipedal robot, two-legged robot
Updated
Two legs define the mobility class
ISO 8373:2021 places the biped robot under legged mobile robots and distinguishes it by travel using two legs. The classification says how the robot moves, not how human-like its complete body is.
A full-body humanoid that walks on two legs is both humanoid and bipedal. A research platform made only from a pelvis and two legs is bipedal without necessarily being humanoid. Conversely, an upper-body humanoid on a wheeled base retains human-like morphology but is not a biped robot while using that base.
Bipedal motion alternates constrained contacts
During walking, one or both feet normally support the body while another leg can swing to a new contact. Running and jumping can add flight phases with no ground contact. The controller must coordinate joint motion, balance, foot placement and contact forces even though the floating body pose is not directly actuated.
The MIT notes on highly articulated legged robots show why practical systems often plan footsteps and centre-of-mass motion before resolving a feasible whole-body motion. This decomposition is useful, but the realised motion still depends on friction, impacts, actuator limits and terrain.
Dataset labels need more than “biped”
A biped dataset should state the robot model, leg and foot geometry, joint layout, payload, terrain, footwear or contact material and whether external support was used. It should distinguish commanded gait from measured contact state and record falls, catches and safety interventions.
Motion captured from a person is not yet biped-robot data. Retargeting must account for the target robot’s dimensions, joint limits, mass distribution, actuation and contact constraints before the motion can be treated as physically executable.
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Related terms
Hardware & control
Humanoid robot
A humanoid robot is a robot whose body is modelled on the human form, typically with a torso, head and limbs, so it can move through human spaces or use human-scale tools and interfaces. The term describes morphology, not intelligence or autonomy; wheeled, partial-body and simplified-hand designs are also sometimes classed as humanoids, so the robot's actual configuration should be stated.
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
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.
Hardware & control
Floating base
A floating-base model represents a robot’s root body with six unconstrained spatial degrees of freedom—three for translation and three for rotation—instead of fixing it to the world. Those base coordinates are not directly actuated; a legged robot changes them through joint motion and external contact forces.
Hardware & control
Whole-body control
Whole-body control coordinates a humanoid’s full multibody state, actuated joints and environmental contacts to pursue several motion or force objectives while respecting constraints such as balance, joint limits and friction. It is a family of hierarchical or optimisation-based methods, not one algorithm; implementations may output joint positions, accelerations or torques.