Building Line Following and Food Following Robots

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Building Line Following and Food Following Robots
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A simple robot
Some of the simplest robots are called
Braitenberg Machines (Braitenberg Vehicles,
Braitenberg Faces).
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Back to basics
A suitable vehicle needs the following - a left
motor (LM) - a right motor (RM) - a left sensor
(LS) - a right sensor (LR)
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Back to basics
A suitable program needs the following - a way
of driving each motor as a function of the
reading on the sensor on the opposite side
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Back to basics
And the environment needs to ensure that the
change in sensory inputs produced by the movement
of the vehicle leads to some interesting and
obviously useful behaviour with a simple
performance measure so that we can have a
competition
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Constraints
All vehicles will have to be run in exactly the
same environment The only suitable sensors are
light sensors
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Consider the termite
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How termites work
Termites (and many other trail-following insects)
follow trails by sensing concentrations of
special chemicals (pheromones) using their
antennae.
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How termites work

• They use a technique called osmotropotaxis.
• Roughly speaking,
• their left legs go at a speed controlled by the
  strength of the sensory input to their right
  antenna,
• their right legs go at a speed controlled by the
  strength of the input to their left antenna
• In other words, they operate just like little
  Braitenberg vehicles, and this enables them to
  follow trails.

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Could we make visible trails on the ground, and
sense them with light sensors?
Yesthere are some trails on the floor of the
arena
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But surely
if the trail is either black or white, wont the
sensors only ever give maximum or minimum
readings? No, because the sensor takes in
reflected light from an area, not a point. If the
area is wholly inside the black region, youll
get the minimum reading (with some noise) And if
its wholly inside the white region, youll get
the maximum reading (with some noise)
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But surely
if the trail is either black or white, wont the
sensors only ever give maximum or minimum
readings? No, because the sensor takes in
reflected light from an area, not a point. If the
area contains both black and white regions if
the sensor is somewhere on the borderline then
the reading will be somewhere in between the
minimum and maximum (again, with some noise)
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A basic strategy
If we space the sensors so that they are
separated by just less than the width of the
trail, then when both sensors read the minimum,
we know we must be on the trail and so moving
forwards is a good idea
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A basic strategy
If the sensor on the left reads the maximum, and
the sensor on the right reads the minimum, we
know were moving off the trail to the left so
turning right is a good idea
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A basic strategy
If the sensor on the right reads the maximum, and
the sensor on the left reads the minimum, we know
were moving off the trail to the right so
turning left is a good idea
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A basic strategy
And if both sensors read the maximum, you know
youve completely lost it Of course, you could
devise some cunning way to get back on the trail
(termites do)
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But
What if one or both sensors give a reading
somewhere in between? The quick and dirty
solution keep on doing whatever you were doing
it wont last The elegant solution you can
produce one if you want, but it wont make any
difference
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The performance measure
We can break this into two stages (1) How far
down the trail you get (2) If you make it to the
end, how long it took
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First, catch your robot

1. You can make whatever you like, but since time is
   so short I recommend that you use a version of
   the Trusty robot
2. Described in Jonathan Knudsens The Unofficial
   Guide to Lego Mindstorms Robots