With belt speed in m/s and drum diameter in metres, the drum speed in rpm is n = v × 60 / (π × D). If there is no chain or pulley in between, this value is the gearbox output speed.

Example

  • Belt speed 0.75 m/s, drum diameter 0.30 m
  • Drum speed: 0.75 × 60 / (3.14 × 0.30) ≈ 47.8 rpm
  • Motor 1,450 rpm → i = 1,450 / 47.8 ≈ 30.3 → standard ratio 1/30
  • Actual values: 1,450 / 30 ≈ 48.3 rpm; belt speed 48.3 × 3.14 × 0.30 / 60 ≈ 0.76 m/s

Use the outer diameter of the drum including lagging; lagging thickness can change the speed by a few per cent. Once the ratio is found, the torque is calculated separately: belt pull multiplied by drum radius gives the torque needed at the gearbox output. Motor options for conveyor drives are on the conveyor belt electric motors page.