I have chosen to replicate the shoulder.
Given the above diagram and thinking about which hinge would allow for the full rotation of the shoulder, I remembered the ball joints laying around my dad’s shop.
The ones I purchased look like this:
The hip joint does not do the same kind of rotation that the shoulder does.
The photo below illustrates the problem (that is the maximum angle of rotation once the dowel has been inserted):
And put the dowel through a bit of aluminum.
And put a dowel in the piano hinge.
And then attached the hinge to the bit of metal:
So then I needed a counter-weight so that the “arm” would rest like it would on the body.