Don’t build to max dimensions. Make your robot as small as possible. Even shrinking a few inches off of your length and width can save a lot of weight due to the Square-Cube law.
FEA isn’t really worth it for FRC. Just build it, test, and iterate. Iterate towards good functionality first, then iterate on weight. If it doesn’t break, keep taking material away. Make it out of thinner sheets or extrusion profiles. Change steel to aluminum. Change aluminum to polycarbonate. Change polycarbonate to thinner polycarbonate. Reduce the infill on 3D printed parts. Once it horrifically breaks, back up one revision.
Think twice about pneumatics. Only use them if you need at least three separate small binary actuations. A complete pneumatics system gets heavy, fast. Don’t use any pneumatic cylinders with greater than about 14 inches³ of stroke volume (equivalent to Ø1.5" bore x 8" stroke). I know you are thinking, “but this Ø2” bore x 24" stroke cylinder seems perfect". It’s totally not. See prior point.
Use the smallest possible wheels, gears, timing belts, etc. Don’t use 8 inch wheels when you can use 3-4 inch wheels. Smaller wheels require less gear reduction for the same effective robot speed. Wheels get lighter, you need less gearing, etc.
Robots and mechanisms don’t have to be indestructible anymore. Without the bag, robots only need to survive a single competition. Assuming we’re in a post-COVID world, you can easily gut your robot and replace and/or rebuild a lot of mechanisms in between events now. This allows you to use even lighter materials or “sacrificial anode” type components / structure.
Reduce the size of all fasteners. Unless you are screwing into a tapped hole or interfacing with a specific component that expects a specific diameter bolt, replace all 1/4"-20 hardware with #10-32. Replace all #10-32 with #8-32. Replace all #8-32 with rivets. If a fastener is simply holding two or more static members together in shear, default to use rivets. These riveters are awesome.