[MrBasse]

Our lightest robots ever have had full steel superstructure built from 1/2 inch square steel tube. In 2011 we were ~85 lbs. and in 2013 we were right around 105 lbs.

We found that with a steel frame we used so much less material for the same strength.

Another benefit is when you hit something wrong, you just bend it back. Aluminium sure doesn't play as nice in that regard.

We use aluminum alot now simply because so many nice COTS items interface with common aluminum extrusions.