CSCI 108 Lab 6
In this lab you will implement line following. Using only light sensors,
your robot will follow a path marked out as a black line on a white
surface. With minor modifications, it should also follow a light-colored line
on a dark surface.
In addition, your robot will need to follow the path politely. If it
bumps into anything along the way (another robot, for example), it should
wait a bit, allowing the other robot to move out of the way.
Preparing the robot
You will need one or two light sensors for this lab. (While either option
can work, I found that the two-sensor implementation stays on track
much better than the one-sensor implementation.) These should be mounted
on the front of your robot, centered and pointing down toward the ground.
You can put them close together, or you may separate them a little bit
(so that they straddle the line, for example).
Implementing line following
A simple algorithm for two light sensors
The path your robot needs to follow will not be a straight line. Even if
it were a straight line, following it would be tricky. (Lab 4 probably
convinced you of this.) You will need to constantly monitor the light
sensor(s) and make adjustments to the motors to keep the robot on track.
If you have two sensors, for example, you can continuously compare
their readings. If the right light sensor is detecting brighter light
than the left, it means that the robot has moved off the black line to the
right and an adjustment needs to be made to the left. If the left light sensor
is detecting brighter light, the robot has moved off the line to the left;
an adjustment needs to be made to the right.
Brightness and darkness are subjective
How can you measure brightness and darkness? What we humans see as
"bright" or "dark" can vary from person to person. Similarly, you have
discovered that your sensors don't all perceive light in exactly the
same way. Some sensors will provide light readings in the entire
range of 0 to 255; others will have a smaller range. So comparing their
readings directly won't necessarily be helpful. In class
we had to think about how to adjust for these different ranges, while
normalizing sensor readings so that they always fell in the range 0-100.
This week you might find it valuable to use the normalizing function
we discussed in class. This will allow you to easily compare the
relative light/darkness detected by each of your sensors.
Implementing the complete program
As described above, your robot should do line following, but it should
do so politely. That is, the robot should wait a bit if it bumps into
another robot, allowing the other one to move out of the way.
The bumper sensing component of your program should monitor the left and right
touch sensors on the front of your robot. If either of these is pressed,
the robot should stop, wait for some short amount of time (a couple of
seconds), and then start to move again.
Testing the vehicles
I have created an oval track using black tape on a white surface. All
robots should be tested on that track.
In addition, with just a minor modification, your robot should be able to
follow a light-colored line on a dark surface. Make the necessary changes to
your program, and test the robot on the track set out on the carpet in the lab.
You will need to demonstrate your program to me.
Please also turn in your program, both on paper and electronically.
This lab must be completed by Monday, October 27 at 10:00 PM.