Arduino-based line follower robot using Pololu QTR-8RC line sensor

UPDATE FEB 2012: This guide is featured on Adafruit's blog
http://www.adafruit.com/blog/2012/02/14/arduino-based-line-follower-robot/

This is Faz3a II, my first line-following robot, which I also hope to use for maze-solving. I used the Arduino Uno, Adafruit motor shield, Pololu's QTR-8RC line sensors and motors. You can build a cheaper and lighter version of this robot using the Atmel Atmega328 and the L293D h-bridge. This robot weighs about 300gm and costs about $90 USD.

For my previous robot projects, I used an empty external hard disk enclosure as the robot platform. But for this robot, I am using a DVD case. All in all, I found the round shape of the DVD case a better choice for maneuverability.  Not to mention the low cost of DVD cases and ease of stacking layers to hold more parts, with the help of long screws and nuts.

For this project, my task was simplified by the availability of software libraries from Pololu and Adafruit for the sensor and motor shield respectively.

Of course I could have bought a robot kit but I want to be able to take my robot apart anytime to build another one or use the parts in a different project. So if your passion is robotics, consider getting a ready robot kit. 

PARTS LIST

ELECTRONICS
Arduino Uno
Adafruit motor shield
Pololu QTR-8RC line sensor. I used only 5 sensors.
Pololu 30:1 micro meta gearmotor X 2
7.2V (6 X AA NiMh batteries)

MISC
DVD case
Wires
Wire straps
3 long screws and about a dozen nuts to act as raisers. The length of the screws depends on the height of the battery brick. One thing to keep in mind when choosing the screws is to get the ones with smooth curved heads and not the flat ones. I use the screw heads as casters. 

SOFTWARE
Arduino IDE 1.0
Adafruit motor shield library
Pololu QTR-8RC Arduino library

REFERENCES
I wrote a guide no how to use and test the Pololu QTR-8RC line sensor.


 

Step 1 Making the robot's plaform from a DVD case

I used a DVD case for the platform. I marked this DVD case with an erasable pen first. It's a rough sketch made with a small ruler. I know this design won't be winning any engineering awards, but it works. Then I used a plain cutter and drill bits to carve out the design on the DVD into the final platform ready for attaching parts. Make sure you drill holes big enough for the wire straps.

Comments

[Bigbadwolf_argh]

How do you wide the motors and line sensor?

[techbitar]

If you review my code you will see which pins are doing what.

[AndresGalaviz]

What exactly assigns or in what units are
#define KP .2
#define KD 5
Got a little lost right there O: BTW excellent robot! Very fast

[techbitar]

These are constants you can experiment with for best PID results. There are plenty of excellent tutorials out there to explain PID controllers. See link below to a site had in my fav list but there are plenty of PID guides that can explain with varying degrees of detail. It's not necessary to understand the theory behind PID, just how to apply it for optimum results. For my robot, the K values are typically tweaked via experimentation.

http://www.chibots.org/index.php?q=node/339

[AndresGalaviz]

Thank you very much, that link was of great assistance for my project.

[techbitar]

super :)

[kumaran201]

Hi,
I have arduino UNO, Pololu QTR 8 RC sensor array, MOTOR DRIVER 1A dual tb6612fng, two geared motor can u help me with procedure and coding for line follower.

[techbitar]

You will find plenty of useful info in this guide.

[TedRobotBuilder]

Nice work! But I don't see how you kept the Arduino from resting with only 7.2V supplied? O.o

[techbitar]

Thanks.

As for resetting concerns, let's analyze the robot:

-- Arduino Uno: 5V @ 500 mA (max)

-- Motors: 6V @ 40 mA free run / 360 mA stall X 2 = 720 mA (max)

500 + 720 = 1220 mA

I don't know how much the motor shield draws but when you consider I am using 6 X 2500 mAh NiMH 1.2 V AA batteries, that leaves me with 1280 mA. This is assuming max power draw from Arduino and the motors. There's plenty of power in the battery brick to power this robot.

[TedRobotBuilder]

The Uno really wants 9V, it's in the specs. The Uno's AVR chip wants 5V but the Uno's board has a regulator on it that expects to see about 9V (but can handle as much as 20V). I have built robots sending the Uno less then 9V but I normally run into resetting issues, like when the batteries start running down or the motors stall. If you aren't hitting any issues that's cool but you might be very close to the limit such that if you add a senor you could run into issues. Also, you could run the batteries longer if you had more headroom. Thanks for the feed back! :D

[techbitar]

Also, most of my uses for the robot is demos/races lasting a few minutes so that's why I don't run into reset issues when using a fully charged power brick. But I am sure if I need to use the robot for extended periods, I will use a voltage booster to be on the safe side.

[techbitar]

http://arduino.cc/en/Main/ArduinoBoardUno

Arduino Uno Summary
Microcontroller ATmega328
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limits) 6-20V

[TedRobotBuilder]

Yeap, 7-12V recommended, your 7.2V is at the low side assuming you are using the Vin pin and not the 5V pin. I assume you have some big caps on your lines to stop any spikes.

[techbitar]

you will find the this links instructive as to the specs of the motor shield and the different ways it gets its power. hope this helps

http://www.ladyada.net/make/mshield/parts.html