Warhound Waist templates...

Now for the ring/joint/pivot you'll need a tube 1.75" in diameter, and it should be thick... this is the keystone of your Titan. 

You need to cut it so it will fit the notch-shape in the Warhound's body.

There's some detail on the back of the waist, just use bitz and wire for that. Pistons connecting the hips should be ~1/8th of an inch thick.