I have a question regarding inertia and friction between gears. I have a gear which is connected to the rod at one end and an electric motor which is connected to the other end. I know the torque of the rod and I want to calculate the torque of the motor I need. I have been told that I can't lay on transmission ration only and I also have to include the calculations of the inertia and friction between gears.

Can please someone explain me how should I do it (every example will appreciated).


1 Answer 1


To turn your gear from rest, you'll need to overcome the inertia of your entire system (rod and gear).

Torque = inertia x angular acceleration. You'll need to figure out what angular (rotational) acceleration you need/can get from your motor. You can approximate inertia with I = (1/2) x mass x radius^2.

You can approximate gears being 95% efficient if you're using spur gears (straight teeth). This means 5% of the energy put in is being lost as friction. So your required motor torque = (operating torque + acceleration torque)/ 0.95 efficiency [friction].


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.