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Can Not Validate VW MMoI Data


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I am having a hard time trying to retrieve the 3D properties for a simple extruded rectangle. In particular, I am trying to find the MMoI (Mass Moments of Inertia) for it. I am using this simple shape as a test to determine if the VW calculations coincide with my calculations before I move on to the actual more complicated parts that we need this information for in order to run our simulation software. At this point the MMoI does not match my calculations. In design layer, I placed the origin at the CoM (Center of Mass) using "next mouse click is zero (0,0)" in the set origin command. Any tips?

-please see attached

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Guest Frank Brault

Hi Al,

Not sure what might be the problem. One thing to try is to set the origin using the "Set origin to drawing center" option. This would correct the calculation of the underlying code uses the hard-wired default drawing origin rather than the User set origin.

hth,

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Thanks Frank,

It is still giving me wonky numbers for Mass Moments of Inertia (x,y,z) that are not even close to what it should be. Even MMoI for a sphere are incorrect. The numbers are all the same, which is right, but the the numbers are incorrect. It seems like I have tried everything! I appreciate your input.

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  • Vectorworks, Inc Employee

Noticed MikeG working on this case and thought I'd post the results here too:

This was apparently an issue in Vectorworks 2012 with 3D Properties/Mass Properties calculation and was fixed in 2013, so it now works in Vectorworks 2014 as well. Unfortunately it was found too late for it to be added to the last patch of Vectorworks 2012 (what this initial calculation was done in)

Give it a shot in the trial of Vectorworks 2014 and see if Vectorworks' math then matches your own:

http://www.vectorworks.net/trial/form

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