Page 300 - Anatomy of a Robot

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MECHANICS 285
Abrasion
This is a measure of the ability to withstand repeated rubbing and use. Some materials
will not abrade much at all. Others will not only abrade but shed harmful particles
as well.
Creep

Materials subject to steady pressure will tend to give over time, or creep. Plastics, start-
ing their life as liquids, are subject to creep. For much the same reason, metals can creep
some. Just make sure that the tolerances of the robot will be maintained over time in the
face of creep.
So which materials should be used in a robot? All the aforementioned factors have
to be considered, but here are some guidelines based on applications:

Home project If the robot is a home project, aluminum is not a bad choice. It’s
cheap, easy to get, lightweight, easy to alter by machine, and relatively strong.
Industrial floor If the robot is for nonmobile industrial use, consider steel for
its durability. If the volume of manufacture is high enough, consider plastics.
Consumer If the robot is for commercial release, consider plastics.
Space If money is less of a problem than weight and strength, consider the more
exotic metals like titanium and composites. Many new considerations come into
play for space-born robots that must face severe G forces, extreme temperature
ranges, vacuum, radiation, and so on.

Some Cautions

The choice of materials can introduce other problems. A few are mentioned in the fol-
lowing sections.

DISSIMILAR METALS’ GALVANIC CORROSION
It’s never a good idea to put dissimilar metals into a robot, at least not if they come
into contact with each other. Action at the atomic level can set up currents and cause
corrosion. This is a particular problem in the marine environment where salts can get
at the metal junction. Do not forget that fasteners must be taken into account as well. If