Line Follower Robot
Our Line Follower Robot
Line followers are one of the
most prominent kinds of robots. They have existed for a very long time,
however, the technologies used for building them have changed rapidly. Earlier,
controller boards the size of bricks were used, but now they have shrunk and
become tremendously powerful. Now, technology allows you to build a line
follower in just under 10 minutes if you have the parts for it. So enjoy
building this quick and easy line follower. Have fun with this DIY hacking
tutorial!
Required Materials
Hardware :
1.
Arduino / Arduino Clone or make your own custom Arduino board.
2.
Two continuous rotation servo motors like this: Continuous rotation servo.
3.
A ball caster: Ball caster.
4.
An infrared sensor array like this: Pololu QTR-8A IR sensor array OR
a set of six IR Leds and Detectors.
6.
Two robot wheels, select
wheels after checking if they fit in the servo.
7.
Chassis, usually a small acrylic board will do.
8.
Four AA Duracell batteries and battery holder.
Software
:
1.
Arduino IDE.
How Does it Work?
The workings of a line follower
robot are pretty straight forward. These robots have the capability to detect a
black/dark line on a lighter surface depending on the contrast. They estimate
whether the line underneath them is shifting towards their left/right as they
move over them. Based on that estimation, they give respective signals to the
motors to turn left/right so as to maintain a steady center with respect to the
line.
These robots usually use an array
of IR (Infrared) sensors in order to calculate the reflectance of the surface
beneath them. The basic criteria being that the black line will have a lesser
reflectance value (black absorbs light) than the lighter surface around it.
This low value of reflectance is the parameter used to detect the position of
the line by the robot. The higher value of reflectance will be the surface
around the line. So in this linear array of IR sensors, if the
leftmost/rightmost IR sensor presents the low value for reflectance, then the
black line is towards the left/right of the robot correspondingly. The
controller then compensates for this by signaling the motor to go in the
opposite direction of the line.
Line Follower Block Diagram
The IR sensor array consists of individual IR
LEDs and IR photodiodes. The IR light emitted by the LED strikes the surface
and is reflected back to the IR photodiode. The photodiode then gives an output
voltage proportional to the reflectance of the surface (high value for light
surface and low for black/dark surface).
IR Sensor Working
Making the Sensor Array for the Line Follower
(Optional)
(Only if you don’t want to buy the Pololu
reflectance sensor)
To make an IR sensor array, take
the six IR LEDs and connect them in parallel with each other. Now, take the IR
photodiodes and place each of them just below the six IR LEDs. Wrap each pair
together using black insulation tape and leaving their tips exposed. Take these
six pairs of IR LEDs and photodiodes and join them in a straight line, each
pair should be 1.5cm apart from the next.
IR Photodiode and IR LED
Taping them together
Assembling the Components for the Line
Follower
Take the piece of acrylic board
and stick the servo motors to the left and right edges using hot glue or super
glue. Then attach the ball caster on the opposite edge. Take the pololu IR
sensor array or your own sensor array and stick it on top of the two servo
motors using a small piece of plastic or foam. The sensor must be positioned in
such a way that it’s about 4-5mm from the ground for optimal performance. On
the top side, stick the Arduino board using double sided tape, do the same for
the battery holder. This is how it looks:
Bottom View
Full View
Connecting the Components Together for the
Line Follower
Setup the hardware connections
with the Arduino and the servo motors. The continuous rotation servo motors are
those types of servo motors that cannot be controlled or set at a particular
angle, unlike normal servos. Servos have three wires coming from them: Red-
Power, Black -Ground, White/Yellow- PWM /PPM Signal. The left servo motor
(white/yellow wire) is hooked up to Arduino digital pin 9 and the right servo
motor (white/yellow wire) to Arduino digital pin 10. The black wires of both
the motors are connected to Arduino GND and the Red wires to the positive
terminal of the battery holder.
Arduino Connections for Line Follower
Using Pololu QTR-8A Reflectance array sensor
If you are using the Pololu
sensor, and you don’t need all the 8 IR detectors. You can remove 2 of them by
cutting at the indicated perforation line on the board. The code we are using
is only for 6 of them. Then solder some header pins to the board for Vcc, Gnd,
and signals 1,2,3,4,5,6. Connect the Vcc and Gnd of this sensor to the Arduino’s
Vcc and Gnd. The signals 1,2,..6 are connected to the Arduino’s analog input
pins A0, A1, A2, …A5.
Using the Custom Fabricated Sensor Array
If you are using the custom
fabricated sensor array, then short the anode terminals of all the IR LEDs
together and connect it to the Arduino Vcc through a 220Ohm resistor. Next,
short the cathode terminals together and connect it to Arduino Gnd. Now,
connect a 10K resistor to the cathode of each of the IR photo-diodes. Short the
free ends of all the 10K resistors together and connect it to Arduino
Gnd. Now, short the anode terminals of the IR photo-diodes together and
connect it to Arduino Vcc. Lastly, connect a wire to the cathode of each of the
IR photodiodes (between the cathode and the 10K resistor). Connect each of the
wires in sequence to tArduino’s analog input pins A0, A1,..A5.
Connections for your custom IR sensor arrayUploading the Code for your Line Follower
The code for the line follower can be found here: DIY_LineFollower. After uploading the code, you need to
sweep/move the sensor array over the black line from left to right for roughly
3 seconds. This is done in order to calibrate and find the max and min values
for reflectance. After that, place the robot on the line and watch the bot
follow it. If you’re using the Pololu QTR-8A reflectance array sensor then no
significant changes may be required, try to check the values coming from the
sensor through the serial monitor. Based on those values, adjust the values in
the code correspondingly.
For those who made the custom
board, find out the rough values of reflectance over the black line and the
outer surface. Substitute these values in the code and calibrate it. You can
use normal black insulation tape as the line for your line follower. You
can see the line follower in action below.
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