Metal
A metal robot is good to visualize, but bad to design and develop and hence is not always the best choice. They are bulky, harder to work with and also expensive. Since metals are good conductors of electricity, a badly designed robot can short and even fry. But if you are seriously into designing a fighting robot, then you should shake hands with metal. Metal can give your robot that rugged look, strength and capability.
Most robots use either Aluminum or Steel; rarely have I found robots using other metals.
Aluminum
This is a soft, light and inexpensive silvery metal which is available in a wide variety of shapes and sizes. One of the most important reasons of using aluminum against other metals like steel is its resistance to rust. Working with aluminum is easier for thin sheets and wires, but tricky for bigger sizes. If you have thin sheets, use a pair of scissors to cut and shape it. Unlike other plastic materials, aluminum can be reshaped, bent, folded and twisted. For thicker sheets and rods, you may need a hacksaw, driller and other standard mechanical tools.
When I started with robots, most of the robot bases were made of aluminum due their availability and ease of use.
Steel
If you need a strong material for your robot, then what is the best selection other than steel? Use steel for body, as support structures, and other parts. Steel balls are generally used for making castor wheels supported by an aluminum casing. Steel is heavier than aluminum, but a good choice for your outdoor and rugged robots. At the same time steel adds additional weight to your robot; hence your motors and battery should be planned such that it can take the weight and still work as expected. Cutting and drilling is complicated compared to other materials. Even thin steel sheets require standard mechanical tools to cut and drill. Thicker sheets are a nightmare to handle. Joining them is another terrifying task as glue and tape turn useless. Soldering does not stand good and you need to either use bolts or nuts or weld steel sheets to join them. Use metals only when you are sure you definitely need them; else go ahead with plastic and polymers.
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