Robot Arduino

CHAPTER 4

Linus the Line-Bot
Let’s begin with a small robot for our first project that introduces the basic concepts of automated
control. This robot decides where to go based on its surroundings and can change its path if the
environment is changed. Linus’ purpose is to follow a black line on a white surface (see Figure 4-1). His
aspirations are quite low, but he is still fun toexperiment with and easy (and cheap) to build.

Figure 4-1. The mostly finished Linus sitting on his track

119

CHAPTER 4

LINUS THE LINE-BOT

The cost of this project as shown is around $80. This includes a commercial motor-driver board, two
hobby servo motors, a homemade IR sensor board, and several other items that might be used for
multiple robots (Figure 4-2).
You also have the optionto substitute your old usable parts like previously used servo motors (or
gear-motors), or maybe you already have a motor-controller, at which point the price for this bot will
drop quite a bit. If you want to save some money, you can also skip ahead to Chapter 6 to find out how to
make your own PCBs on your PC with free software. You can also build these circuits on prototyping
board fromRadio Shack.
We start by making an infrared sensor board so that Linus can detect the color of the surface
beneath him, and then go through the process of modifying a hobby servo motor for continuous
rotation. Next we fit the rear wheels onto the motor output shafts and make a bracket for the front caster
wheel. We then modify a tin container for use as our frame, and install the motors, infraredsensor
board, Arduino with motor-controller shield, and batteries. After everything is wired up, we load the
code onto the Arduino, make a track for Linus to follow, and start testing to see how fast we can get him
to go around the track without losing his path. With Linus complete, you can then add LED interior
lighting, a speed adjustment potentiometer, or paint his frame to add some style.Let’s look at the parts
required to build Linus.

Parts List for Linus
For every project in this book, you are expected to have an Arduino ($35), so we won’t include that in
each project price. In Chapter 6, we build a “poor-man’s Arduino” that is intended to replace your main
Arduino when a project is completed so you don’t have to keep buying new Arduinos–unless you are
rich. The priceper board to build yourself is around $8-$15 each, but they can be programmed only with
an FTDI cable ($15 from Sparkfun.com), because there is no USB interface built onto the homemade
boards.
I also do not include tools or other standard materials (like wire) into each project price, because
these will last for several projects. A roll of solid 22AWG wire should get you through most of thebook, as
should a roll of rosin-core solder. It is also handy to have a few pieces of scrap metal or aluminum on
hand. A 36-inch long piece of flat aluminum stock enables you to make several brackets, supports, or
motor mounts, so I keep a few different sized pieces in my parts bin.
This project uses some basic robotic components: sensors, motors, wheels, a frame, batteries, a
motor-controller,and your Arduino micro-controller (Figure 4-2). If you already have a robot base with
several of these components, you might complete this project for as little as $15 to build the infrared
sensor board.

120

CHAPTER 4

LINUS THE LINE-BOT

Figure 4-2. Here you can see the unassembled parts used to build Linus.
You can also substitute parts to save money as you please: a set ofgear-motors you might have for
the servo motors I used, a homemade H-bridge for the AF motor-controller, or pre-built IR sensors from
Sparkfun.com (item: ROB-09453) instead of building your own. With a little tweaking, any of these
alternatives should work. You can also save money by ordering some parts from Digikey.com, because
you will get far more in quantity for nearly the same price as buying...