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Finding Inertia Values about the centre


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Is there a way to create a macro which would find the inertia of a region out the (0,0)?


Currently, I have to Massprop the object, draw a line from (0,0) to the centre of the object, move the object from the end of the line to the centroid, and then massprop it again to get the correct Ixx and Iyy values.


I have looked into creating a macro for it, but I don't know how to use the initial centre values to move the object to (0,0). Is there a way to do this via amacro?


If not, is there any other method unknown to me to find the Iyy and Ixx values of an object as if it is sitting at (0,0)?


Thanks in advance, hope this all makes sense.

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When you run massprop there is an option to send results to file, what you can do is read this file and using this info move object to the required point then rerun massprop again. Its been a while since I did this. Will have to do a bit of home work.

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  • 1 year later...

I wish ACAD would output the MOI through the centroid for the Ixx and Iyy plus the Ixy. From what I've discovered MASSPROP calculates the MOI's about an axis thru 0,0,0. Is there a lisp routine that would draw short lines through the centroid parallel to the X axis and another short line parallel to the Y axis? A line at the angle of the Izz minimum MOI would also be nice so I could find the distance to the shapes outer fiber to calculate the stress due to bending on the Izz axis.

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