Robot control
Centroidal dynamics
Definition
Centroidal dynamics describe the motion of a multibody system’s center of mass and the evolution of its total linear and angular momentum. External forces and moments determine the rates of change of those momenta.
Also known as: Centroidal robot dynamics
Updated
Summarizing the whole robot
A humanoid has many links, but their combined linear momentum equals total mass times center-of-mass velocity. Its angular momentum about that center includes the contributions of all moving links. MIT's derivation shows how the full system can be summarized through these momentum quantities.
Ground reaction forces, gravity, and other external contacts change the total momentum. Internal joint torques redistribute motion among the links; by themselves they do not create a net external wrench on the complete robot.
Planning useful contact forces
A walking planner can optimize center-of-mass motion, angular momentum, and foot forces before solving for every joint trajectory. Unlike the simplest linear inverted pendulum model, centroidal formulations can explicitly retain angular-momentum changes and more general contact geometry. The survey by Wensing and colleagues compares the simplifications used by different planners.
Connecting momentum to joint motion
A centroidal momentum matrix maps generalized velocity to total momentum for a given configuration. This helps connect the reduced description to whole-body control.
However, the MIT notes warn that simplified centroidal planning can miss joint position and effort limits. A contact-force plan may satisfy momentum balance yet require an unreachable posture or excessive joint torque. Consistency with the full robot must still be checked.
Sources
Related terms
Center of mass
The center of mass is the mass-weighted average position of a body or a collection of bodies. For an articulated robot, its position changes as the links move.
Whole-body control
Whole-body control coordinates a robot’s joints and contacts to satisfy several motion and force objectives together. In humanoids, it commonly combines balance, foot motion, hand tasks, and posture subject to physical constraints.
Zero-moment point
The zero-moment point is a point on a chosen support plane where the net moment associated with the ground reaction wrench has zero components parallel to that plane. In flat-ground walking with the usual contact assumptions, it coincides with the center of pressure.
Model predictive control
Model predictive control repeatedly optimizes future actions using a system model, applies the next part of the solution, and replans from updated state information. It can account for objectives and constraints over a finite prediction horizon.