2.3 · Kinematics, Dynamics, and Contact
A learned policy operates inside the mechanics of the platform. Kinematics determine reachable motion; dynamics and contact determine which motions are feasible, stable, and safe.
- Relate joint state to end-effector pose and velocity.
- Recognize singularity and feasibility constraints.
- Explain why contact creates hybrid, discontinuous behavior.
Forward and differential kinematics
Forward kinematics maps joint configuration to pose. The Jacobian maps joint velocity to end-effector twist and exposes local sensitivity, redundancy, and singular directions.
Dynamics and limits
Inertia, Coriolis effects, gravity, friction, external wrench, torque, power, and acceleration limits bound feasible action. A policy need not model every term explicitly, but the platform always obeys them.
Contact is hybrid
Small pose changes can switch among free motion, impact, sticking, and sliding. Averaging across these regimes can produce an action that is valid in none of them. Controllers and evaluation must reflect the true contact mode.
The robot body is not a rendering target; it is the dynamics that every learned action must satisfy.
