Amon the most often used sensors are the optical ones, which can sense the reflected light intensity, being thus useful for the black or white line following, and for stopping at white or at black lines. They can be mounted in fixed positions, or in slightly moveable, up-and-down positions, to help with passing obstacles.
For our design, since we have the two front-and-vertical 5×7 frames, we decided to put another 5×7 frame in between them, onto which we attached the sensors.
Another advantage of this setup is the fact that the distance between them is close to the width of the lines, so the programs can be written to use one or the other sensor, to better navigate, especially when alternating going “dead reckoning” and following the line.
If the missions are only done by following lines, then they take a very long time, and we cannot accomplish enough of them to earn a good number of points. So oftentimes we decided to mix “shortcuts” with following lines. Thus the robot goes away from the line, does things, and then goes back and “catches the line” again. We can alternate between sensors according to which one allows us to make the move faster and with more precision, building some turns only with the gyro, but then stopping when one of the sensors sees the white or the black part.