TORQUE
Torque is a measurement of twisting ability about an axis. Basically it is a force vector (F) applied at a distance (R) which is measured in ounce-inches, pound-feet, dyne-centimeters, newton-meters or gram (force)-centimeters. For the relationships of these units, go to SHORT DISCUSSION IN PHYSICS  The above shows that torque is constant for all gears or drivers fixed to a shaft. Not shown for clarity, a driver would appear as a larger wheel on the same shaft with the same torque but less force. A good example is a torque wrench, which measures torque at the thread radius of a screw or nut by applying a force at the bar end. GEAR TRANSFER FUNCTIONS Examination should reveal the transfer functions. The (right) driving gear with 20 teeth, 1 inch radius and 2 ounce-inches torque rotates CCW at 200 RPM and and exerts a 2 ounce force on the driven gear with forty teeth for a ratio of 2:1. Ratios are usually stated as driven teeth:driver teeth. NOTE: The following relationships are totally independent of the gear pitch. They also hold true for pulleys using diameter or radius ratio. No slippage is assumed. The direction of rotation is not reversed. If the teeth are of equal size to permit proper mesh, the driven gear must have 2 inch radius. During one revolution of the driver, 20 teeth pass 20 teeth on the driven, resulting in only one half revolution CW, which means the driver must turn twice for the driven to turn once. This produces 100 RPM or a 2:1 speed reduction. Often misunderstood, torque transfer is not quite so obvious. Since the driver output force is at a radius of 1 inch: |
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