Check out the last way about how to calculate MOI.

https://www.youtube.com/watch?v=0RVmxpCk0SE

Posted by: Walter

Check out the last way about how to calculate MOI.

https://www.youtube.com/watch?v=0RVmxpCk0SE

This is for brake based dyno.

Maybe this will help to you:

How do you measure Rotational Inertia (I)?

There are a few formulae for working out the moment of inertia of differently constructed drums / rollers. I'll only deal with the one here. The formula for a solid cylindrical drum / roller made of uniform material is;
I = m/2 * r²

You can calculate the mass of the drum or other components by calculating the volume of the piece and using the density figure i.e. 7900kg / m³ for steel.

Using the dimensions of my drum, I'll calculate it's MOI here.

The drum is 360mm wide, has a diameter of 460mm and has 2 stub axles 120mm X 80mm.

Volume for a cylinder = Pr²* h

V = P * .230m² * .360m
V = 0.0598284 m³ * 7900 (density kg/m³) = 472.6450kg

Now for the Stub axles;
V = P * .040m² * .120m
V = 0.0598284 m³ * 7900 (density kg/m³) = 1.5168kg

Now for the MOI
I = m/2 * r²

The drum;
I = 472.6450/2 * .230²
I = 12.5014kg×m²

The stub axles;
I = 1.5168/2 * .120²
I = 0.02184kg×m² now times 2 there are two of them!

Grand Total of;
MOI = 12.5451kg×m²

(I had my drum weighed and it came up at 476kg, the calculated weight is 475.6786kg. Good enough for me.)

(By the way, notice how much the radius of the cylinder affects its rotational inertia. First of all, the mass depends on the radius squared. A cylinder twice the diameter of another has four times the mass. Then, the rotational inertia is that times radius squared AGAIN. This comes from the particle distribution. Two cylinders with the same mass, but one with twice the radius of the other (i.e. not so wide, but with a bigger diameter), has four times the rotational inertia. This is why I settled on the largest diameter I could get hold of.)

Posted by: sieniu

 I want to put accurate MOI into YourDyno, but i don't have specification to my dyno.

Dyno is bosch LPS 002 with flywheel. I don't want calculate MOI because i don't know inside construcion of rollers. Did someone know MOI value of bosch LPS 002 ? or someone know how to measure MOI of dyno ?

Hello 

What is correct moi for lps002 inierta dyno ? 

Best regards

I’ve got mine set to 13,5 which gives good (real) figures