A base for my high school robotics team's second robot, Discovery.
Some figures of merit for FRC robot chassis are low center of gravity, good manufacturability, and decent stiffness. The design sought to achieve these, keeping in mind that our machining capabilities were quite limited.
I opted for a simple frame made of 1" aluminum box tubing, which could be easily bolted together, and would accommodate our independently-steered (swerve) wheel modules. Simple FEA study showed displacement under expected load was minimal.
It worked pretty well, and that's about it.