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282 CHAPTER ELEVEN
Materials
Robots can be made out of just about anything. The environment and the mission of the
robot often pose severe constraints on the materials that can be used. The Air Force is
hoping to make robot butterflies for reconnaissance. Although it’s true that most cars
are made out of steel, I doubt a steel butterfly would get very far.
Many different materials are available for new robot design, and many considerations
must be made when choosing the materials:

STRENGTH TO WEIGHT

Unless a mobile robot is to be used in sumo wrestling matches or very high winds, it
makes sense to keep the weight down. One way to accomplish this is to minimize both
the amount and density of the construction materials. We have to know the strength of
the material before minimizing the amount used. Shaving material off structural mem-
bers can be a risky game. It requires advanced knowledge of structural engineering and
simulations. Picking a material that is not very dense is somewhat simpler. The key
parameter to look at is the strength-to-weight ratio. Materials that are very strong for
their weight helps keep the weight of the robot down. The selection of such materials is
somewhat complicated by the fact that certain types of strength depend upon the shape
and formation of the material used. For example, a well-folded cardboard structure can
hold far more weight than a single piece of cardboard.
An article on the effect of new materials in designing sports equipment can be found
at www.tms.org/pubs/journals/JOM/9702/Froes-9702.html.
These following web sites and PDF file outline the characteristics of various types
of materials:

www.radshape.co.uk/ (For metals, look under materials.)
www.robotstore.com/download/Muscle_Wire_FAQ_V3.pdf (Actuator materials)
www.mdacomposites.org/materials.htm (For composite materials)

MACHINING AND FORMATION

It doesn’t do much good to have a very strong material if it cannot be formed into the
shapes required for the robot.