If you want to see a really cool material check this out.
Aluminum honeycomb composite
I stumbled across it one day in the McMaster Carr catalog. (a little light reading material
)
Pg 3363
-0.6 lbs/foot^2 for 1/4" thickness
-compare to 3.6 lbs/foot^2 of 1/4" aluminum sheet
I'm not even going to speculate some of the possible uses for this on a FIRST robot. BEWARE the price 8$ -12$ a square foot depending on thickness