Definition: Torque

Torque is defined as:

Force x Moment Arm = Torque

In the English system, torque is measured in "foot-pounds", "inch-pounds", or even "ounce-inches".

In the Metric system, torque is measured in "Newton-meters".

8.851 inch-pounds = 1 Newton-meter

1 foot-pound = 12 inch-pounds

16 ounce-inches = 1 inch-pound

1 Newton = 1 kilogram-meter per second squared

A 1 horsepower (746.0 watt) motor operating at base speed of approximately 1750rpm produces 3 foot-pounds of torque. The formula is as follows:

(horsepower x 5250)/rpm = foot-pounds

(Foot-pounds x rpm)/5250 = Horsepower

Tip: A simple way to determine the torque required to move a load is to connect a torque wrench to the load and take a reading.

<A name=Torque>Torque, Horsepower, and Drives

Dont confuse torque with horsepower. While it is true that standard speed (1750 base rpm) motors all deliver about 3 foot-pounds of torque per horsepower, this is only true if they are running at base speed. A standard speed 1 hp motor running at 50% of base speed is still delivering about 3 foot-pounds of torque, but only requires 1/2 hp of power.

To understand this better, assume that a 1 hp standard speed motor requires 750 watts of power (actually 746 watts). If operated at 50% of base speed, this motor would still deliver the 3 foot-pounds of torque, but would require only about 375 watts of power.

Drives are nominally sized by "horsepower". However, they are actually sized by amps of output current. Therefore, if we had an application where we could guarentee that the above 1 hp standard speed motor would only operate at 50% of base speed, we could provide a 1/2 hp drive.

Here endeth the lesson....................