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ManojWaghmode1-Visitor
1-Visitor
August 2, 2011
Question

CG calculation

  • August 2, 2011
  • 1 reply
  • 3186 views

hello,

I have calculated CG of assembly ASM1 with respective cs0.

also the CG of all child part of Assembly ASM1 wrt cs0.

Now i am taking the avarage of x y and z coordinate of all parts CG and comparing it with the CG- xyz of Assembly ASM1.

the values are different.

can any one please let me know am i doing right practice.

if not please let me know which is correct processes to calculate the CG of assembly if i know the CG of all child.

Regards,

Manoj.


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1 reply

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DavidButz1-Visitor
1-Visitor
August 5, 2011

Imagine a 10 lb. cube adjacent to a 1lb. cube of the same material; the CG is not the average of the 2. Then when you assemble parts of different densities ...

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ManojWaghmode1-VisitorAuthor
1-Visitor
August 6, 2011

Thanks for the reply,

Can you please let me know how it is calculated?

Thanks again,

D
DavidButz1-Visitor
1-Visitor
August 10, 2011

Manoj,

Well, briefly, the actual calculation involves a triple integral summation of density dxdydz. However, that may not be what you really are asking.

Think of parent and child on a see-saw. Dad's cg is in the middle of his body, say 4 feet from the pivot; his daughter's cg is on the other side, say 6 feet

from the pivot. The average of these two cg locations is 1 foot from the pivot on the daughter's side, but, obviously, the combined cg is not there but at the pivot itself, distance zero.

Not to confuse the issue, but, technically, what is being calculated by the software is center of mass, not center of gravity. In a gravitational field they are

not identical because the mass which is "lower" in the field has a greater effect. Thus the moon's center of gravity is closer to earth than its center of mass.

But that's just gratuitous nerdiness for the sake of completeness; we don't have a gravitational field at play within the ProE modeling environment, so center of mass and center of gravity are coincident.

David

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