Torque Sensing (Commutator)

A passive commutator has no sensor: the animal's own rotation, applied through an off-center tether, is the force that turns the rotor. A motorized one must detect the rotation first. A gyroscope (an inertial measurement unit) on the animal side reports the turn as it happens; it rides on a 34 AWG wire bundle under 1 g, or, with a compatible X-Series headstage, its signal travels over the HDMI cable with no separate sensor. A Hall sensor on the rotor reads a magnetic encoder inside the commutator, so nothing is added to the animal, with tracking sensitivity and speed adjustable at the panel or the PC. Either signal drives a low-noise motor with continuous active torque compensation.

The choice is made at order and sets the PRO's configuration: the gyro configurations carry the Neuropixels ports and the HDMI headstage port, with GPIO and the gyro control on the same cable, and suit Neuropixels and behavior, where the head carries little and the response must be immediate; the Hall configurations suit rats and preparations without Neuropixels, where the torque the animal exerts on the joint is enough to be read at the rotor. The two commutators are compared under Commutators, and the decision is worked through in Choosing a Commutator for Freely Moving Recording. Research use only.