Solving For Output Torque With Gear Ratios

Have done calculations for a single 11 watt motor and an 11 watt motor plus a 5.5 watt motor. Keep in mind that I am running both motors on freespin and with a red cartraige in the 11 watt. this is ok because torque compounds whilst rpm stays at 100prm as 5.5 watt will be set to 100rpm. Keep in mind an 11 watt by itself has an output of approx. 2 Nm with an 11 watt and 5.5 watt being approx. 3Nm. I am also running the gear ratio 36:84. Here are my results:

  • TA = teeth on gear 1 (36)
  • TB = Teeth on gear 2 (84)
  • NA = rotational speed/rpm gear 1
  • NB = rotational speed/rpm gear 2
  • TA = torque (Nm) input torque by motor
  • Pout = wattage out
  • Pin = wattage in
  • GR = Gear Ratio

Hope this helps anyone who was struggling to see if they had enough talk.


An 11 watt motor… and your calculations are showing 273 watts… something sounds fishy. Additionally, 273 watts is approx 1/3 of a horsepower… a real stretch for a motor of that size.

I have not taken the time to check formulas/etc, but this doesn’t pass the sniff test.


Like an engineering professor of mine once said, to a classmate:

“You think there’s compression in a rope?”


haha, yes, missing divide by 60. But also an odd way of doing the calculations.