Page 358 - Concise Encyclopedia of Robotics

Wheel-Drive Locomotion
In artificial intelligence (AI), well-structured language is a require-
ment. In that field,the most demanding and complex in computer science,
one must use the most powerful programming techniques available.
Two forms
Robot-controller program structuring can take either of two forms,
which can be called top-down programming and bottom-up programming.
In the top-down approach, the computer user looks at the whole
scenario, and zeroes in on various parts, depending on the nature of the
problem to be solved. A good example of this is using a network to find
information about building codes in Dade County, Florida. You might
start with a topic such as State Laws. There would be a directory for that
topic that would guide you to something more specific, and maybe even
to the exact department you want. The programmer who wrote the soft-
ware would have used a well-structured language to ensure that users
would have an easy time finding data.
In the bottom-up approach, you start with little pieces and build up to
the whole. A good analogy is a course in calculus. The first thing to do is
learn the basics of algebra, analytical geometry, coordinate systems, and
functions. Then, these are all used together to differentiate, integrate,
and solve other complex problems in calculus. In a computerized calculus
course, the software would be written in a well-structured language, so
you (the student) would not waste time running into dead ends.
WHEEL-DRIVE LOCOMOTION
Wheel-drive locomotion is the simplest and cheapest way for a robot to
move around. It works well in most indoor environments.
The most common number of wheels is three or four.A three-wheeled
robot cannot wobble, even if the surface is a little irregular. A four-
wheeled robot, however, is easier to steer.
The most familiar steering scheme is to turn some or all of the wheels.
This is easy to do in a four-wheeled robot. The front wheels are on one
axle, and the rear wheels are on another. Either axle can be turned to steer
the robot. The illustration at the upper left shows front-axle steering.
Another method of robot steering is to run the wheels at different
speeds. This is shown in the upper-right illustration for a three-wheeled
robot turning left. The rear wheels are run by separate motors, while
the front wheel is free-spinning (no motor). For the robot to turn left, the
right rear wheel goes faster than the left rear wheel. To turn right, the left
rear wheel must rotate faster.
A third method of steering for wheel-driven robots is to break the
machine into two parts, each with two or more wheels. A joint between

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