Not exactly structural, but we used polycarbonate this year as guides for our conveyor (
easier to see when zoomed in), which also served to center the ball for the shooter. We used a heat gun to bend the pieces and the distance between them when attached to the robot was slightly smaller than width of the boulder where the guides gripped it, so the ball was slightly compressed while it was being held there. The flexibility of the polycarbonate gave us a firm grip that hugged the ball really nicely. The guides were 1/4" at one point, can't remember if that was the final thickness used or not.
Other uses of polycarb on this year's robot were chain guards, CDF manipulator (linkages on the bottom of the intake), bellypan, sides of our winch spools, and the
top of our conveyor (added to block the ball from flying up and out of the robot after being grabbed).