All of our robots we have ever made have used 1/2 inch steel box section. Its cheap, light, easy to weld and strong. Our robot stood up to me jumping up and down on it (and i am around 15 stone ) so its pretty strong. We even made a small "featherweight" for robot wars thing here once out of it. Its just really good
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One of the factors you didn't mention was price, which is a definate problem for us, we have to pay for entry and get there from uk, costing more in flights than any of the US teams (not sure about the brazilians)...
In america sponsorship is much more easy it would seem :\ its like getting blood from a rock here lol
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