Motor torque comes from the relation 9550 × P / n. The gearbox reduces speed by the ratio and raises torque by roughly the same ratio; the loss in between is deducted through gearbox efficiency (η). In short, T2 ≈ 9550 × P × η / n2, or T2 ≈ T1 × i × η.

Example

  • Motor: 2.2 kW, 1,450 rpm, rated torque 14.5 Nm
  • Ratio 1/30 → n2 ≈ 48.3 rpm
  • Loss-free upper limit: 14.5 × 30 ≈ 435 Nm
  • Actual output torque: 435 × η; η is taken from the catalogue according to gearbox type and ratio.

Worm gearboxes have lower efficiency than helical types, and it generally drops as the ratio grows. So with the same motor and ratio, a worm gearbox can deliver noticeably less output torque than a helical one. Taking η as 1 in the calculation leads to an undersized motor when the torque requirement is tight.

Motor-side torque values by power and speed are in the electric motor torque table article.