Hardware

Joint Coupling

Joint coupling is mechanical or kinematic interdependence between joints, where actuating one degree of freedom produces motion or torque at another. It arises by design in differential wrists, tendon-driven fingers, and underactuated hands, where fewer motors drive more joints, and as a parasitic effect in cable-routed transmissions; either way it requires a coupling matrix or model in the kinematics and control stack.

Why it matters for physical AI

Coupled, underactuated designs cut cost and weight in hands and wrists, but their nonlinear motor-to-joint mappings complicate calibration, simulation fidelity, and the action spaces exposed to learned policies.