# Shaft Torque

In a DC Motor whole of the electromagnetic torque (T) developed in the armature is not available on the shaft. A part of it is lost to overcome the iron and mechanical (friction and windage) losses. Therefore, shaft torque (T_{sh}) is somewhat less than the torque developed in the armature.

**Definition:** Thus, in the case of DC motors, the actual torque available at the shaft for doing useful mechanical work is known as** Shaft Torque.** It is so called because it is available on the shaft of the motor. It is represented by the symbol T_{sh}. The output of the motor is given by the equation shown below where T_{sh} is the shaft torque in r.p.s and the N is the rotation of the motor in r.p.m. The shaft torque is expressed as

The difference between the armature torque and the shaft torque ( T_{a} – T_{sh} ) is known as the lost torque and is due to the formation of the torque.

**Brake Horse Power (B.H.P)**

In the case of the motor, the mechanical power available at the shaft is known as Brake Horse Power. If T_{sh} is the shaft torque in Newton Meter and N is the speed in r.p.m then,

The output brake horsepower is given by the equation (1) shown above.