Question

how to get the center of mass of an irregular shaped object?

Answer 1

The most practical way depends on the object. If you can divide the shape into two areas of equal mass in two different way then the spot where the two divisions meet is the center of mass. Of course if the shape has any symmetry then you have your first division along the axis of symmetry.

If it is an irregular shape made up of regular shapes then you can find the center of mass of each sub-shape and the weight of each sub-shape. The coordinates of the center of mass is then the coordinates of center of mass of each sub-shape weighted by their weights.