Gearbox Ratio and Reflected Inertia

WHAT THIS SCREEN ANSWERS

A gearbox changes more than speed. It trades motor speed against output torque and transforms the inertia the motor feels. That inertia transformation is squared, which is why a ratio that looks modest can materially change acceleration performance. This page puts speed, torque, and reflected inertia beside one another before a motor and gearbox become a locked pair.

Enter the reduction ratio as output-to-motor reduction, the output load inertia, output torque, output speed, and a supplier-supported efficiency estimate. MechPlane divides load inertia by the ratio squared, multiplies output rpm by ratio, and translates output torque back through the ratio and efficiency. The three results expose the basic trade: more reduction lowers reflected inertia and motor torque while increasing motor speed.

There is no universal ideal ratio. A high ratio may improve inertia matching but push motor speed, gearbox input speed, backlash, or efficiency into an undesirable range. A low ratio may preserve a slow motor speed but leave too much inertia at the motor. The right comparison depends on the actual load cycle, component curves, cost, packaging, and positioning requirements.

The result is deliberately limited to a simple kinematic and energy relationship. Gearbox internal inertia, torsional compliance, backlash, tooth loading, thermal limits, shock, and allowable overhung load remain outside it. Use the page to form a candidate envelope, then confirm the specific gearbox with current supplier data and continue to the motor duty screen.