Material selection is a lot of fun, and there are strengths and weaknesses to all materials. The weaknesses of solid wood (in robots) are that it has low impact resistance at the point of impact -- the fibers in the wood can crush or get gouged out, and that the joint between metal fasteners and the wood can be a weak point. The good things about wood are that it has incredible strength in compression (think "tall tree") and is light for its stiffness. Dave Gerr in his book "The Nature of Boats" has several chapters on the different common hull materials for pleasure boats: fiberglass, wood, steel, and aluminum. You'd like the book: the title of one chapter on materials is "Even From Cheese Whiz (Almost)," in which Gerr posits out that the important thing is matching the material to the purpose, not picking "the best" material, which he claims doesn't exist.
It's interesting that Gerr says that when you remove cost of construction (where fiberglass wins), and maintenance (where aluminum is best), the material that works the best for boat hulls in the yacht range is Douglas fir, when looking at strength and stiffness per pound of material. When we built the FRC robot "Wooden Thunder" four years ago, we created side bumpers out simple 2x4 Douglas fir boards planed down to 1.25" thick. We took some terrific bashes from other robots, including one that gouged out a chunk of wood an inch long and a half-inch deep, without any damage that would have actually hurt the robot.
A single layer of 6-ounce woven fiberglass cloth, or even better 12-ounce biaxial fiberglass set in epoxy on each side of the frame will increase the breaking strength while adding very little weight. My #2 son did a middle-school science project which consisted of cutting 1x6 "white wood" boards from Home Depot into blocks, and then gluing the blocks together. He then tested the glued joints to destruction using a mechanism we built together. The results were kind of fun. As you'd guess, superglue was terrible on wood. The joints failed before the material in nearly every sample. "Gap filling" superglue was just about as bad. Polyurethane glue ("Gorilla Glue") worked well when the blocks were clamped very tight. In some samples where the clamping wasn't perfect, the glue lines failed, and in other samples the wood split before the glue line. Yellow carpenter's glue and epoxy joints held perfectly -- the material failed before the glue line. The fun samples were the ones where he used epoxy, and then epoxied a single layer of 6-ounce fiberglass cloth on both sides of the joint. In the reinforced sample, the wood broke at the edge of the cloth in every case, and we had to add so much weight that we nearly broke our test mechanism before the wood broke. If I remember correctly, the super glue joints failed at about 40 pounds of applied force, and it took more than 150 pounds before the reinforced blocks broke -- and not in the reinforced area. Six-ounce cloth is called that because it weighs six ounces per square yard, so the builder could reinforce that frame with a lot less than a pound of 'glass and epoxy. (When I quote weight, we were applying the force along a very narrow edge pressing directly on the joint with a lever arm holding 5-gallon paint buckets into which we placed rocks as weights -- the weight is the weight of the rocks, not a scientific "pounds per square inch" measurement -- it was middle school.)
I buy most of my marine epoxy and glass from System Three (
www.systemthree.com), but there are several good brands. Stay away from polyester resins, which simply don't hold as well as epoxy. Make sure you keep the epoxy off your skin by wearing long sleeves and gloves and if you do a LOT of epoxy work, you might want to wear a $25 respirator. Partially cured epoxy can be BAD to sand, as the particles easily trigger skin allergies. If you want to sand your 'glassed and epoxied frame after construction, wait as long as you can before sanding it (like a week or longer), and wear long sleeves, long pants, a respirator, gloves, and use a sander hooked up to a shop vac. Epoxy WON'T cause cancer, as far as we know today, but it can trigger allergies, and the more often you have contact, the more likely you are to get a reaction. I've been doing epoxy boat building and maintenance (hobby, not pro) for about five years and I sometimes get a little redness on my skin for a day or so, and I have repeated contact and am careful. Like any other construction method, learn about and follow the safety rules.
Anyway. Using lumber (instead of plywood) for the frame of a robot is a terrific idea. It's nature's own composite material, and the way that frame is laid out makes good use of its strengths. If it was me, I might use lumber with a lower specific gravity than red oak, and then not drill speed holes, but I have nothing against the one in the pictures. Please tell the woodworker that it's pretty.