Torque Definitions

Torque is the product of a force and the radius at which it is applied. The British unit of torque is pound-feet and in smaller motors this unit is reduced to ounce-inches. The metric unit of torque is Newton-meter. 

Few motors produce a single value of torque over their entire speed range so that a torque vs. speed curve is often necessary for torque evaluation. Definitions of terms used to describe specific points on the curve are listed below along with definitions of some other commonly used terms for motor torque specification.

Pull-In Torque: the maximum torque at which a synchronous motor (stepping motor included) can accelerate its load to synchronous speed. 

Pull-Out Torque: the maximum torque which a synchronous motor (stepping motor included) can develop and still maintain synchronous speed. 

Full-Load Torque: the torque developed by a non-synchronous motor at its rated full-load speed. 

Breakdown Torque: the maximum torque that the motor can develop; it occurs as a point on the speed-torque curve below synchronous or full-load speed. #FengTech Motor 

Locked-Rotor Torque: the torque developed with the rotor at standstill. 

Holding or Static Torque (Stepping Motor): the torque required to displace the rotor from its equilibrium position with one or more stator phases energized with the rotor at rest. 

Detent or Residual Torque (Permanent Magnet Motor): the torque developed in an unenergized motor when the permanent magnet rotor is displaced from a position of minimum stator eluctance.