Mark, we (1899) were probably the team you are thinging about, while our frame was aluminum, the arm was all wood. We did get a lot of visitors to the pit looking the arm. Interesting enough our spare arm, hung at the back of the pit was painted and most people assumed was metal (I had several questions as why we switched from alum to wood), whereas the one on the bot was unpainted. A photo of the arm is
http://www.popularmechanics.com/tech...c=rss#fbIndex5
The truss section weights 2.5lb (wood only), the arm including motors, wiring, preloading, etc weighs < 19lb.