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A closer look at motor torque and torque multipliers

Publication date: 
October 2004
Cyndi Nyberg Esau, Former EASA Technical Support Specialist

The basic definition of torque is the measure of the force applied to produce rotational motion, usually measured in pound-feet or Newtonmeters. Torque is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied. Torque = Force x Radius Obviously, if the force is increased, the torque will increase. If the magnitude of the force is maintained, but the radius is increased, then the torque is also increased. When this principle is applied to a sheave, chain or belt system, the effect of increasing the radius is to slow down the driven load, while increasing the torque. The basic torque equation is: Torque = Horsepower x 5252/rpm Speed and torque have an inverse linear relationship, which means that however much the speed is decreased, the torque will increase by the same percentage. For a motor system with sheaves, the horsepower in the above equation stays constant, but by lowering the final speed of the driven equipment, the final output torque can be increased without a change in the driving motor's power rating.