Hardware

Flexible Joint

A flexible joint is a robot joint exhibiting non-negligible elasticity between the actuator and the driven link, arising from compliant transmissions such as harmonic drives, belts, or deliberately introduced springs as in series elastic actuators. The elasticity adds unactuated dynamics that can cause oscillation and complicates control, motivating techniques like full-state feedback on motor and link positions, or singular perturbation approaches. It also provides beneficial shock tolerance and force sensing.

Why it matters for physical AI

Compliance protects hardware and humans during unexpected contact and enables torque estimation from spring deflection, but the added dynamics must be modeled or learned for precise, high-bandwidth manipulation.