1. Oct 27, 2014

### zoom1

I have a motor with rotor inertia of 140gcm2 with 71:1 gearhead.
Considering this configuration what would my inertia be at the output ?

140*(1/71)2 ??

2. Nov 1, 2014

### Greg Bernhardt

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

3. Nov 1, 2014

4. Nov 4, 2014

### Gmen

Let me make a try.
By rotor inertia you mean the rotor's moment of inertia, I suppose. This is a characteristic of the rotor and does not change. It sounds like asking how much the mass of a car would change depeding on its engine (or gearbox ;) ).

What/why are you asking such a question?

5. Nov 17, 2014

### Dr.D

Let the motor mass moment of inertia be J, and let r be the gear ratio, such that
theta-out = r*theta-motor
If the inertia of the gears is neglected, the system kinetic energy is
T = (1/2) J * theta-motor-dot^2
= (1/2) J * (theta-out-dot)^2/r^2
So the apparent MMOI, as seen at the output shaft is
Jout = J/r^2