Build Your Own Combat Robot

Chapter 11: Autonomous Robots 249
can help correct the problem by placing a small infrared filter in front of the receiving
lens to block the bright light effects. A good one can be obtained from
photography stores. One such filter is a Kodak Wratten #87 gelatin filter, or the
#87C filter. Using this filter will yield normal distance measurements in bright
light conditions.
Shock could damage the sensors. In the ring, robots can hit with such intense force
that mechanical shock is a primary concern. Although the sensors are robustly
built, if jarred hard enough, their precision optics can move enough to affect the
sensor. To handle this, you should mount the sensor with rubber grommets.
Sensing: It’s a Noisy World Out There
Often, when people first start using sensors in robots, they find the results are not
quite what they expect. Most sensors used in robotics are subject to a great deal of
interference, variation, and changing results due to the ever-changing environmental
conditions. As a result, many people become rather frustrated that the results
from the sensors change and give occasional false readings.
Consider an infrared sensor in a room full of infrared sensors. Because the sensor
is looking for the light it generates with its infrared emitter, the light generated
by other emitters in the room can confuse the detector and cause false readings.
Similarly, a sonar detector in a noisy room may hear echos and sounds from itself
or other sensors that cause false readings.
Humans suffer similar kinds of problems, but we have amazing abilities to correct
the sensory input we obtain. When a sailor first walks on a ship, the rolling of
the vessel in the waves can make him or her walk a crooked line or stumble
around. Very quickly, typically in one or two days, the sailor’s brain will adjust
and compensate for the swaying ship so that the sailor doesn’t even realize the
boat is swaying after awhile.
This sophisticated adjustment and compensation is one of the most unique
things about the human brain. The human brain also combines, or “fuses,” the input
from our vision, inner ear (balance), and pressure in our feet to keep us standing
up. If one of these types of input changes, our brains can quickly adapt.
Robots need a similar ability both to combine the sensory input from several
sensors and to adapt to changes in the function of the sensors. This is done in sophisticated
autonomous robots using neural nets, Bayesian networks, genetic algorithms,
and other complex computation. Your robot need not be this
sophisticated to take advantage of sensors, however.
Techniques for Improving Sensor Input
Some sensors have built-in techniques that clean up the signal they create. Sonar
detectors, for example, emit a “ping” in specific sound frequency ranges and ignore
input from other frequencies. This helps filter noise and avoid interference
from other sounds in the sensor’s environment. Similar approaches are used with
infrared detectors using filters and lenses to avoid unwanted wavelengths of light.