ATM RE: Formula for centroid of a semi-circle

["Sidor . Kurt" <KSidor@drc.com>]

Ken,

Your math skills are just fine!  The location of the centroid of a semi
circle is (4*R)/(3*pi) units from what what would have been the center of a
full circle.  However if you descide to remove a few "chunks" from the
interior of this shape to lighten things up the centroids position will
shift.  The method for calculating the new centroid involves translations of
moment of inertia formulas relative to some reference axis for the
particular geometries of your removed sections.  Since your math skills seem
just fine, I'm sure this would not be too much more of a "head-scratcher".
The easy way, if you have CAD software, is to simply draw it and have the
computer tell you the centroid point.  I think some of the shareware CAD
programs can do this.

Good Luck!

Kurt Sidor
Mechanical Engineer
Dynamics Research Corp.
Encoder Division