# How do I calculate moment of inertia in a wheel?

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1. Feb 22, 2015

### shannonxtreme

What I have are two wheels, weight assumed at 50 kg overall for both, joined by an axle. The wheels are 900 mm apart from the centre of one tire to the centre of the other. The diameter of the tire is 690 mm. How do I calculate the moment of inertia in order to find the torque in the centre of the axle?

For the torque calculation I know the angular acceleration is -0.43rads^-2

2. Feb 22, 2015

### Staff: Mentor

For a real system like that, you would either use FEA modeling or do a physical test. Do you have access to a dyno?

EDIT -- Or do you have access to the physical system? You can use a falling weight on a rope to calculate the moment of inertia MOI with an experiment...

3. Feb 22, 2015

### shannonxtreme

Nope, I do not have access to any testing equipment right now. I'm assuming its a perfect system, just need the theory right now. Testing and implementation when I have access to materials :)

4. Feb 22, 2015

### Staff: Mentor

How much experience do you have with MOI calculations? You can approximate the MOI with several component pieces...

5. Feb 22, 2015

### shannonxtreme

Little to no experience other than basic theory. I'm doing this as my final project for my bachelors, and my project supervisor says I don't need to make it over complex because I just don't have the experience

6. Feb 22, 2015

### Staff: Mentor

So model the system with a series of disks and shafts, and add up the MOIs of the components. They add linearly.

So model the axle as a shaft, the wheels as disks, and the tires as a combination of disks and the outer bands. Each component will have the appropriate density (steel or rubber). Does that seem do-able?

7. Feb 22, 2015

### shannonxtreme

That actually does! Thanks a million! I won't be able to do that for my interim report tomorrow but this will help a great deal :)

8. Feb 27, 2015

### Dr.D

What MMOI do you want to find? What is your reference axis?