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I NEED HELP WITH MATHS - moments of inertia
MK9R - 21/7/09 at 10:21 AM

Lets see if you clever locostbuilder fellows can help me with this (its been a long time since i was in the classroom)

I have been given some mass moments of inertia calculations at work, but i need to find out some of the parameters to enter into another data sheet.

I 've been given the moments Ix, Iy and Iz, the mass, The distance of the centre of gravity in Axis Z and the combined distance (hypo) in X and Y. I need the X and Y dimensions. I tried working back the formulas Ix=m(y2+z2) but results are comingout strange, any idea what i am doing wrong. Here is some sample data:-

Ix = 2.1 kg/m2
Iy = 6.91 kg/m2
Iz = 8.32 kg/m2
Z = .311 m
XY = 0.083
Mass = 105kg

My calculations were coming out that X was .176m and Y is .277m which is obviously wrong

coozer - 21/7/09 at 10:38 AM

Should there not be another input to determine the XY ouputs correctly?

MK9R - 21/7/09 at 10:44 AM

quote:
Originally posted by coozer
Should there not be another input to determine the XY ouputs correctly?


i used
Ix=m(y2+z2)
Iy=m(x2+z2)
Iz=m(y2+x2)

but it hink this must be the wrong thing to use as i can't get the results to tie up. I may be barking up completely the wrong tree, like i say its been a long time!! I used to get 90-100% in this subject at uni, but not used it for years and my brain is now pickled

mad4x4 - 21/7/09 at 11:23 AM

In Iz=m(y2+x2)

is m not Gradient of line defined as

dy/dx or (y2-y1) / (x2-x1) for x-y planes.