# Static Mass Balance

#### kashoo

What is the procedure of static Mass Balancing of any assembly which has a total mass of 100 kg with subsystems which would assemble in it is ranging from 2.5 to 10 kg ...
i think to hang the complete system freely in air and then checking the placement of exact cenetr is an appropriate method.
Is there any standard (like ASTM etc) for this particular testing.

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#### FredGarvin

We used to hang objects from three different points to determine CG. I can't think of anASTM spec for that though.

#### kashoo

What would those three points...Our Assembly is just like a cubical box....so whould we hang copmlete assembly form its top surface?

#### FredGarvin

It's been a while since I have done this (college) but, IIRC they were just random points spread out over the body. We used to do this for wierd shapes like automotive seat assemblies.

#### minger

Yes, hand the object from three points. If the object is an extruded object (like...a 2-D object with constant cross section and some thicknes), then you simply hang the object from three points and draw a vertical line from that point straight down. Where the three lines intersect is the CG (in the center of the body of course). If your three lines intersect to form a triangle, then simply find the center of the triangle to find the center of the body.

Try this link for a lecture I remember for a lab that was on finding an objects center of gravity and moment of intertia:
http://www.eng.utoledo.edu/~cciocane/courses/mime3390_041sp/lec/m3_center_of_mass_and_mass_moment_of_inertia_lecture.doc [Broken]

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#### FredGarvin

Minger,
After browsing that you reminded me of the test we would do to determine the mass moment of inertia of rotor disk assemblies. The pendulum test works pretty well once you get the hang of it. It really isn't necessary now with complex models and Pro/E. Occasionally we have a legacy piece that that test still needs to be performed.

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