Starting torque

This is defined as the torque measured when a predetermined voltage is applied to the motor or when the motor starts moving extremely slowly by applying a predetermined current. Figure (a) shows the T/N characteristic (torque vs. speed characteristic) of a squirrel-cage induction motor, and (b) the characteristics of a permanent magnet type DC motor.

As indicated by the ☆ symbol in fig.(b) the opposing torque that is needed to reverse the motor slowly is larger than the starting torque. When friction caused by the bearing is negligible, half of this difference gives the braking torque due to hysteresis in the iron core.

Shidou torque is the Japanese term designated by the Institute of Electrical Engineers, but it is often referred to as kidou torque in industry.