Page 54 - Robot Builder's Bonanza

LOCOMOTION SYSTEMS 23

Robots can have just about any number of wheels, although two is the most common. The
robot is balanced on the two wheels by one or two free- rolling casters, or perhaps even a third
swivel wheel or nonmoving skid. Four- and six- wheel robots are also around. You can read
more about wheel designs in Chapter 20, “Moving Your Robot,” and the many hands- on
projects in Chapter 26, “Build Robots with Wheels and Tracks.”

TRACKS

The basic design of track- driven robots is pretty simple. Two tracks, one on each side of the
robot, act as giant wheels. The tracks turn, and the robot lurches forward or backward. For
most robots, each track is about as long as the robot itself.
Track drive (see Figure 2-11) is practical for many reasons, including the fact that it makes
it possible to mow through all sorts of obstacles. Given the right track material, track drive
provides excellent traction, even on slippery surfaces like snow, wet concrete, or a clean
kitchen floor. See Chapter 26 for some affordable tracked robots you can build yourself.

LEGS
Of all types of mobile robots, those that walk on legs present the greatest challenges. But
they’re also great conversation pieces! You must overcome many difficulties to design and
construct a legged robot. First, there is the question of the number of legs and how the legs
provide stability when the robot is in motion or when it’s standing still. Then there’s the ques-
tion of how the legs propel the robot forward or backward, and— more difficult still!—the
question of how to turn the robot so it can navigate a corner.
Your walking robots can have two or more legs. The fewer the legs, the more challenging
the design. Two- legged (bipedal) robots use unique balancing methods to keep them from
falling over. Four- legged robots (quadrupeds) are easier to balance, but good walking and
steering can involve adding extra joints and some sophisticated math to make sure everything
moves smoothly.
Robots with six legs (called hexapods) are able to walk at brisk speeds without falling and are
more than capable of turning corners, bounding over uneven terrain, and making the neighbor-
hood animals run for cover. As a result, the six- legged kind, like the one in Figure 2-12, are the
most popular among robot makers. You can read about building your own leg- based robot in
Chapter 27, “Build Robots with Legs.”

Figure 2-11 Tracks on a robot
provide mobility on uneven or thick
terrain like sand, grass, or rocks. Tracks
may be made of rubber, plastic, or metal;
the plastic ones are among the easiest to
use and the least expensive.

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