The location of the mass center of a collection of parts is compued by finding the point about which the mass moment is zero, (in other words, the "average" mass moment). This is done as follows;
1) Compute the mass moment of each part of the system:
Mass moment = position vector (of CG) x mass - this gives the mass moment about the x, y, and z axis.
2) sum all of the mass moment vectors (Total x, y, and z moment)
3) divide the total moment vector by the total mass (sum of all the masses)
This is a vector that points to the location of the mass center.
(Note that all of the position vectors must be in the same reference frame. The resulting mass center is in this reference frame)
