# How to obtain the moment of inertia of the rotor?

I need to measure or calculate the moment of inertia of the rotor in order to simulate a DC motor in computer simulation. Is there a procedure that can be followed to measure or calculate the moment of inertia without special lab equipment? Thanks

• There are some torsional pendulum methods that can found by searching the internet.
– user80875
Commented Apr 23, 2017 at 2:10
• Perhaps you can try to identify the time constants from a step response? Commented Apr 23, 2017 at 3:42
• You can use a weight on a string, wrapped around a shaft or pulley to accelerate the rotor. The applied torque is known. The acceleration of the rotor as the weight falls will allow you to approximate inertia. Assuming drag is low. Commented Apr 23, 2017 at 4:08
• It's only useful to know the moment of inertia of a mtor if you're going to try and build some control system. So, suggest you just crack on and build a position servo with straight feedback to coil current. The circuit will oscillate (when you know the inertia you can stabilise it later). From oscillation frequency and the value of the position to current gain you used, you can calculate the effective rotor inertia. Commented Apr 23, 2017 at 6:52
• If you have (or can make) an accurate model of the rotor something like Solidworks will calculate the moment of inertia about the centroid of mass. Commented Apr 23, 2017 at 11:58