Hardware

Torque Ripple

Torque ripple is the periodic variation in an electric motor's output torque as its rotor turns, arising from cogging between magnets and stator slots, non-ideal back-EMF waveforms, and current measurement or commutation errors. In robot joints it produces velocity fluctuations, vibration, and acoustic noise that are most pronounced at low speeds, degrading smooth trajectory tracking and clean force estimation. Mitigations include skewed magnets, optimized windings, and ripple-compensating current control.

Why it matters for physical AI

Smooth low-speed motion and clean proprioceptive force sensing both suffer under ripple, which matters for robots that estimate contact from motor currents instead of dedicated force sensors and for precision tasks like polishing and insertion.