Moment of inertia

[Freedom Fries]

Has anyone constructed a test rig to measure actual moment of inertia values? I'm considering it to measure things like motor parts, purchased wheels, and other items that aren't accurately modeled.

[Freedom Fries]

Has anyone constructed a test rig to measure actual moment of inertia values? I'm considering it to measure things like motor parts, purchased wheels, and other items that aren't accurately modeled.

[Buckingham]

You don't really need a "rig". Hang it from some strings, push it so it oscillates rotationally, and measure the natural frequency and you can figure out the inertia.

The other option is to accurately model them.

Before you do an analysis on the quantitative effects of inertia on vehicle performance (or any parameter for that matter), you should run uncertainty calcs to determine the following:

Find the sensitivity of your output to your input. From this you can determine the largest change in inertia that will yield no significant change in vehicle performance. The uncertainty of your intertia measurement need only be less than this. Then design your test or measurement to only be as accurate as it NEEDS to be.

As far as the inertia of your wheel, a 15 min. solid model or some simple hand calcs on representative shapes could be all you need. Its also quite possible that knowing the mass of the wheel and assuming it is a 13" OD x 6" thk disk of uniform density is all you need to do.

What if the difference between that outlandish assumption and a 99.99999999% accurate value of inertia results in only .00001 seconds of difference in lap time (which is the only real output you should ever concern yourself with)?

Those are just numbers I am throwing out there, but the point is that there probably isn't any realistic gains to be had by designing and building an inertia measurement rig.