Weight Concerns

[Rick TYler]

Originally Posted by Gdeaver

I've posted before on this. Take a piece of 1/4" Birch or Oak plywood, some 6oz. s-2 fiberglass cloth and some laminating epoxy. Put one layer of fiberglass on each side. The strength is amazing. Cost - 4'x4'x1/4" 24$, 1 qt. epoxy 18$. 2 yard x 60" S-2 6oz. cloth 16$ per yard. Put some fiber in your robot's diet and you'll loose weight.

My sons and I built a 17-foot expedition canoe last summer. It has a hull made of 4mm Okoume plywood with layers of 6-ounce glass on the inside and outside. It weighs about 60 pounds, which is at least 15 pounds less than an aluminum canoe of similar length and width. The biggest advantage of metal over plywood (even a glass/ply composite) is that metal has better puncture resistance. The ply/glass composite will be stiffer and stronger for the same weight -- or weigh less for the same stiffness and strength. Lexan is really strong, but for its stiffness it is heavy.

Last season, Wooden Thunder was hit so hard that our 1/4-inch birch plywood electronics shield actually cracked -- but it protected the controller. It took us 10 minutes to cut and fit a new one, which was installed in time for the next match. Light, strong, and easy to repair are all advantages of good plywood.

I swear that some year we are going to build a robot that is all hand-laid composites, and only uses metal for gears, conductors, pulleys, chains, and stuff like that. The towers I designed for Woodie last year would have been 3-inch diameter carbon fiber-fiberglass-epoxy composites on a foam core. They would have only weighed a couple of pounds for both of them, and would have been insanely strong. I was outvoted by conservative teenagers (curse them...). Really, the biggest shortcoming of epoxy-laminated composites in FIRST is that you have to really plan ahead on your connections and attachment pads. You can't just run a bolt through a carbon fiber column in any old place.