Follow a line

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Introduction

There a multiple different methods (algorithms) to follow a line. We show two simplest methods (which can be coded with a huge variety), also zig zag linefollower and proportional line follower. See the linked pages for more references. The line can be drawn on a huge paper, or made by using black (or colored) tape. The easiest line is smooth, but it might contain very sharp turns. However, the line should not cut itself.

Robot

Any robot (with tires or treads, perhaps walking robots too) will work.

Sensors

One light sensor or color sensor is needed.

Theory

These algorithms follow the border of the line, not the line.

Calibration

The color sensor should be calibrated, either in the program using black and light reflectances, or by calibrating the values from the sensor. See the linked page for more information.

Zig Zag

Zig zag algorithm turns to right if sees white, and to left if the sensor is on the black. Or vice versa. The algorithm is easy to program using only one if block. The speed and turning value need to be considered and adjusted.

Proportional

The proportional line follower steers according to the value read from the color sensor. The sensor is assumed to be calibrated, so that at value $c=50$ the robot will go straight. Define a steering function

$s(c)=2c-100$.

It is clearly seen, that

$c$	$s(c)$	Does
0	-100	Steer left
50	0	Go straight
100	100	Steer right

The coefficient is $2$ which makes the robot steer rapidly. You might wish to have smaller or larger steering effect depending on the path. The steering function can be generalized easily to

$s(c)=k(c-50)$

which allows to test different steering coefficients $k$. This is easy to implement in Ev3-G programming language.

Exercises

This course is supported by Meet and Code. The course is made in collaboration with Robotiikka- ja tiedekasvatus ry.

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