I was wondering if you could guide me in my choice of material in one of my projects. I must design a robot capable of being very cost efficient, light, and durable. What material is best suited for this? It's difficult to research this sort of information on the internet, due to such a high amount of material classifications. In one of my books, Plywood, Steel, and Aluminum are said to be very Strong, and Steel is said to be the most cost effective. However, there is no information regarding weight. Also, is "Strength" necessarily equal to "Durability" ?