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5.4 Case Study: Unmanned Ground Robotics Competition
trate on what the robot should do, not how it will do it, although often the
designer sees both the what and the how at the same time.
In the case of the CSM entry, only one behavior was initially proposed: follow-line.
The perceptual schema would use the white line to compute the difference between
where the centroid of the white line was versus where it should be, while the motor
schema would convert that to a command to the steer motor.
In terms of expressing the behaviors for a task, it is often advantageous to
BEHAVIOR TABLE construct a behavior table as one way of at least getting all the behaviors on a
single sheet of paper. The releaser for each behavior is helpful for confirming
that the behaviors will operate correctly without conflict (remember, acci-
dently programming the robotic equivalent of male sticklebacks from Ch. 3
is undesirable). It is often useful for the designer to classify the motor schema
and the percept. For example, consider what happens if an implementation
has a purely reflexive move-to-goal motor schema and an avoid-obstacle be-
havior. What happens if the avoid-obstacle behavior causes the robot to lose
perception of the goal? Oops, the perceptual schema returns no goal and the
move-to-goal behavior is terminated! Probably what the designer assumed
was that the behavior would be a fixed-action pattern and thereby the robot
would persist in moving toward the last known location of the goal.
Behavior Table
Releaser Behavior Motor Schema Percept Perceptual Schema
always on follow-line() stay-on-path(c_x) c_x compute-centroid(image,white)
As seen from the behavior table above, the CSM team initially proposed only one
behavior, follow-line. The follow-line behavior consisted of a motor schema, stay-on-
path(centroid), which was reflexive (stimulus-response) and taxis (it oriented the ro-
bot relative to the stimulus). The perceptual schema, compute-centroid(image,white),
extracted an affordance of the centroid of white from the image as being the line. Only
the x component, or horizontal location, of the centroid was used, c_x.
Step 5: Refine each behavior. By this point, the designer has an overall
idea of the organization of the reactive system and what the activities are.
This step concentrates on the design of each individual behavior. As the
designer constructs the underlying algorithms for the motor and perceptual
schemas, it is important to be sure to consider both the normal range of envi-
ronmental conditions the robot is expected to operate in (e.g., the steady-state
case) and when the behavior will fail.
The follow-line behavior was based on the analysis that the only white things
in the environment were lines and plastic covered bales of hay. While this was a
good assumption, it led to a humorous event during the second heat of the competi-
tion. As the robot was following the white line down the course, one of the judges