How to use Gearbox Ratio& Output Torque Calculator
- Enter Motor rated power (kW) and adjust the options as needed.
- Run the tool and inspect its results, evidence and limitations.
- Copy or download the result, then verify it against the actual website, source data or business records.
Try a concrete example
7.5 kW 4-pole motor (1450 RPM) driving a helical gearbox (ratio i = 25, 95% efficiency) through a 120mm sprocket: output speed is 58 RPM with 1172.93 N·m (119.6 kgf·m) nominal torque. Applying 1.4x service factor requires a rated torque ≥ 1642.10 N·m. Sprocket tension yields 19.55 kN overhung load Fr (~1.99 tonnes force); ensure output bearings tolerate 19.5 kN or enlarge sprocket pitch diameter.
How to interpret results
Gearbox sizing hazards include broken shafts, burned bearings, and sheared gear teeth. Neglecting service factor fB risks shock overload failure during motor start; ignoring overhung radial loads Fr from sprockets or pulleys causes early shaft fatigue.
Frequently asked questions
What is gearbox service factor fB and how is it selected?
Service factor fB is the core safety standard established by SEW and Flender. Motor nameplate power reflects steady-state load, whereas cyclic reversals, shock loading, and starts induce peak stresses. Uniform conveyor duty uses fB = 1.1~1.3; cranes and agitators with moderate shock use fB = 1.4~1.6; heavy shredders and rock crushers require fB ≥ 1.8~2.0.
Why do sprockets or pulleys on the output shaft cause overhung radial loads?
Direct shaft couplings transmit pure torsional torque without radial force. Sprockets, belts, and gears exert heavy transverse tension on the shaft overhang (Fr = 2000 × T / d × kr). Smaller sprocket pitch diameters d yield much higher radial forces. If Fr exceeds catalog ratings, mount sprockets closer to the housing shoulder or increase pitch diameter.
Why does worm gearbox (NMRV) efficiency differ drastically across gear ratios?
Worm gearing transfers motion via continuous sliding friction. Small ratios (i = 7.5~15) have steep lead angles achieving 82%~86% efficiency. High ratios (i > 40~60) feature shallow angles with physical self-locking, dropping efficiency to 65%~70% where 1/3 of input power turns into heat. For continuous duty, helical or helical-worm reducers save substantial power and run cooler.
How does gear ratio calculation prevent motor mismatch or gearbox mechanical failure?
Output torque scales as T2 = T1 × i × η. High ratios of 50~100 amplify even a 1.5 kW motor to over 1000 N·m. If the machine jams, motor rotational inertia will shear gear teeth instantly. Install mechanical torque limiters, shear pins, or VFD electronic torque clamping.