Catweazel, AKA Michael Leefers, was kind enough to create computer-rendered instructions for building TrotBot in LEGO, and share them with us! Instead of using 3/16" aluminum rods to prevent TrotBot's inner frame from sagging, Catweazel cleverly added a Technic beam to connect the inner frame to the outer frame, which helps to prevent the plastic support axles from bowing. This is the same solution I was planning on using for the support rods of my large bamboo TrotBot - great stuff!
You can access or download Catweazel's instructions and efficiently purchase parts via his Rebrickable page. Thank you Mr. Leefers!