/diy/ - Do It Yourself

I've been thinkin' of doing the same thing.
You could try looking into getting some Revoltech joints.
They're joints used for Revoltech action figures, and allow a good range of movement granted you don't glue the joints into the holes. Really they're just ratchet joints, but you can buy them by themselves for fairly cheap. They even come in different sizes, and I believe you can even buy the double-joint kind. You can find some here: http://www.hlj.com/scripts/hljlist?Word=revoltech&Dis=2&DisplayMode=images&Sort=std&
qid=AWO7IMTVS3Q&set=1&q=1&MacroType2=dolcloth
They're usually 4 dollars for 6 of them.
What you can do is make your mannequin, cut out the places where you want movement, and make snug holes to put the Revoltech joints in.

The problem with mire armatures is that they eventually snap off, same with the plastic if you're constantly moving it. With action figure joints you can interchange them or replace them if they ever break, so you won't ruin your whole mannequin.