Students with no design experience are often not sure how to approach this process
of designing parts for dynamic applications. The following suggestions are offered to
get you started. As you gain experience, you will develop your own approach.
It is often useful to create complex shapes from a combination of simple shapes, at
least for first approximation dynamic models. For example, a link could be considered
to be made up of a hollow cylinder at each pivot end, connected by a rectangular prism
along the line of centers. It is easy to calculate the dynamic parameters for each of these
simple shapes and then combine them. The steps would be as follows (repeated for each
link):
1 Calculate the volume, mass, CG location, and mass moments of inertia with respect
to the local CG of each separate part of your built-up link. In our example link these
parts would be the two hollow cylinders and the rectangular prism.
2 Find the location of the composite CG of the assembly of the parts into the link by
the method shown in Section 11.4 (p. 531) and equation 11.3 (p. 524). See also Figure
11-2 (p. 526).