Gearbox Motor Torque Guide
A gearbox motor torque calculation checks how a motor behaves after speed reduction. It links motor power, motor speed, gear ratio, gearbox efficiency, and duty factors. The calculator uses these values to estimate input torque, output speed, output torque, usable rated torque, and force at a driven radius. It also compares available torque with a known load torque.
Why Torque Changes
A gearbox trades speed for torque. When the ratio increases, output speed falls. Output torque rises by the same ratio, but only before losses. Real gearboxes lose power through friction, oil drag, bearing load, and gear mesh heat. Efficiency accounts for those losses. A worm gearbox may need a lower efficiency value. A helical or planetary gearbox may use a higher value.
Design Factors
Service factor adjusts the result for shocks, starts, stops, and duty hours. Safety factor adds an extra reserve. These factors do not create more torque. They reduce the torque that should be treated as safely usable. This is important when a conveyor starts loaded, a mixer sees uneven material, or a hoist must avoid overload.
Power and Speed
Motor power and speed define motor shaft torque. A low speed motor creates more shaft torque at the same power. A high speed motor needs a larger ratio to reach slow output speed. The output power is lower than input power because efficiency removes losses. The output speed is motor speed divided by gear ratio.
Using the Result
Start with nameplate motor power and rated speed. Enter the selected gearbox ratio. Use measured or catalog efficiency when possible. Add a realistic service factor. Use a safety factor for uncertainty. Enter load torque if it is known. Then compare usable torque with load torque. A positive margin suggests the selection may work. A negative margin means the motor, ratio, or gearbox rating should be reviewed.
Engineering Notes
Torque calculators support early sizing. They do not replace manufacturer ratings. Check thermal limits, shaft loads, bearing life, duty cycle, lubrication, mounting position, brake loads, and start frequency. Also confirm that the gearbox rated torque exceeds the calculated design demand. For critical equipment, verify results with test data and approved electrical design practice before final purchase approval.