Understanding Torque For Gears, Pulleys or Chain

Torque has two units: length and a force. The typical unit of measurement is Nm or Newton-Meters. Newton is the force and meters is the length. Since we are dealing with small motors, we will use oz-in (ounce-inch) as the units, ounce being the force and inch being the length. The length is the measurement from the center of the shaft and the force is the amount of force it takes to turn the motor shaft at the length from the center of the shaft. torque = length * force So, there is always a relationship of the amount of force that the motor will be able to turn the shaft with where the force is located from the center of the shaft.

To determine the torque using a gear or pulley ratio: TorqueOut = TorqueIn * GearRatio Example (leger gear on motor): TorqueOut = 100 oz-in * 1:2 = 100 * 1/2 = 50 oz-in Example with the gear ratio reversed (smaller gear on motor): TorqueOut = 100 oz-in * 6:1 = 100 * 6/1 = 600 oz-in