Torque in Gear Drive Design

There is one key issue that many users of power transmission equipment have when detailing their requirements with us; underestimating the torque requirements of a particular drive.

Many is the time a customer will say “it is only going very slowly” without realising that this is how a lot of torque is generated.  Most gear drives utilise a four pole electric motor (1400 RPM) on the input and reductions generate torque as a function of their ratio. 

When converting motor design power for a particular job into the output torque, the following formula is used:  Torque (Nm) = (Motor Power (kW) x 9550) / Speed (RPM of output shaft).  As we can see, the denominator is speed, so the slower the unit is going, the less we divide by and the higher the torque value.  In American terms, Torque (in lb-ft) = (Motor Power (HP) x 5252) / Speed (RPM).

Very large reductions will require a very large gearbox, usually with an electric motor that looks tiny in comparison and out of place.