You will need several mechanical and electrical components for this project apart from the Arduino Yún. The first set of components is for the robot itself. You basically need three things: a robot base or chassis that will support all the components, two DC motors with wheels so the robot can move around, and at least one ultrasonic sensor in front of the robot. We used a mobile robot kit from DFRobot (http://www.dfrobot.com/) that you can see in the following image:
The kit is called the 2 Wheels miniQ Balancing Robot chassis and costs $32.20 at the time of writing this book. Of course, you don't need this kit specifically to build this project. As long as you have a kit that includes the three kinds of components we mentioned before, you are probably good to go on this project.
For the motors, note that the circuit we used in the motor shield can handle up to 12V DC, so use motors that are made to work at a voltage under 12V. Also, use motors that have an integrated speed reducer. This way, you will increase the available torque of your motors (to make the robot move more easily).
For the ultrasonic sensor, you have many options available. We used one that can be interfaced via the pulseIn() function of Arduino, so any sensor that works this way should be compatible with the code we will see in the rest of this chapter. The reference of this sensor at DFRobot is URM37. If you plan to use other kinds of distance sensors, such as sensors that work with the I2C interface, you will have to modify the code accordingly.
Then, you need an Arduino board that will directly interface with the DC motors via a motor shield. At this point, you might ask why we are not connecting all the components directly to the Arduino Yún without having another Arduino board in the middle. It is indeed possible to do with the sensors of the robot, but not the motors.
We can't connect the motors directly to an Arduino board; they usually require more current than what the Arduino pins can deliver. This is why we will use a motor shield that is specialized in that task. Usually, the Arduino Yún can't use these motor shields without being damaged, at least at the time of writing this book. This is due to the fact that motor shields are usually designed for Arduino Uno boards and the wrong pins on the shield can be connected to the wrong pins on the Yún. Of course, it would also be possible to do that with external components on a breadboard, but using a shield here really simplifies things.
This is why we will interface all the components with a standard Arduino board and then make the Yún board communicate with the standard Arduino board. We used a DFRduino board for this project, which is the name that DFRobot gave this clone of the Arduino Uno board. This is as shown in the following image:
Of course, any equivalent board will work as well, as long as it's compatible with the official Arduino Uno board. You could also use other boards, such as an Arduino Leonardo, but our code has not been tested on other boards.
Then, you need a motor shield to interface the two DC motors with the Arduino Uno board. We also used a motor shield from DFRobot for this project. The reference on the DFRobot website is 1A Motor Shield For Arduino, as shown in the following image:
Again, most motor shields will work for this project. You basically need one shield that can command at least two motors. The shield also needs to be able to handle the motors you want to control in terms of voltage and current. In our case, we needed a shield that can handle the two 6V DC motors of the robot, with a maximum current of 1A.
Usually, you can look for motor shields that include the L293D motor driver IC. This integrated circuit is a chip dedicated to controlling DC motors. It can handle up to two 12V DC motors with 1A of current, which will work for the mobile robot we are trying to build here. Of course, if your shield can handle more current or voltage, that would work as well. The important point to look for is how to set the speed of the robot: the IC I mentioned can directly take a PWM command that comes from the Arduino board, so if you want to use the code prescribed in this chapter, you will need to use a shield that uses a similar type of command to set the motor's speed.
Finally, we added a simple prototyping shield on top of the robot to make power connections easier and so we can add more components in the future, as shown in the following image:
Again, you can use any equivalent prototyping shield, for example, the official prototype shield from Arduino. It is mainly so you don't have many cables lying around, but you can also use it to extend your robot project with more components, such as an accelerometer or a gyroscope.
You will also need a power source for your robot. As the DC motors can use quite a lot of current, we really recommend that you don't use power coming from your computer USB port when testing the robot or you will risk damaging it. That's why we will always use a battery when working with the motors of the robot. We used a 7.2V battery with a DC jack connector, so it can be easily inserted into the Arduino Uno board. This battery pack can also be found on the DFRobot website. You can also use some AA batteries instead of a battery pack. You will have to make sure that the total voltage of these batteries is greater than the nominal voltage of your DC motors.
As for the software itself, you don't need anything other than the Arduino IDE and a web server installed on your computer.