Race around the world

source code of this tutorial

---

Summary

In this tutorial, we are going to discover the basics of kilobot programming. This simple bunch of code will make a single kilobot race along a track in loop.

The code in this tutorial is written for this racetrack. The kilobot starts the race with its front leg on the red point. Note that you can adapt it to any race track you want.

---

What you will learn

• Basic template for a kilobot program
• How to make the kilobot flash color with set_color()
• How to make the kilobot move with set_motors()

---

Basics

If you have already read the coding for kilobots guide, you already know that a kilobot program is divided in two main parts : the setup() function and the loop() function. The setup() function is only executed once, at the very start of the execution, and the loop() function is executed again and again until the kilobot is told to stop.

The following sections will illustrate how these two components work to build a simple behavior for the kilobot.

---

The setup() function

Before the kilobot starts racing along the track, we are going to make it flash like the flashlight at the beginning of a real race. As this code is only ran once at the start, we are going to place it in the setup() function :

void setup() {
    // Blinks red, yellow and green before startup
    set_color(RGB(1,0,0));  // red
    delay(1000);
    set_color(RGB(1,1,0));  // yellow
    delay(1000);
    set_color(RGB(0,1,0));  // green
}

---

The loop() function

The sequence of actions that a kilobot must do to race a single loop around the track will be placed here.

void loop() {
    // Goes straight
    spinup_motors();
    set_motors(kilo_straight_left, kilo_straight_right);
    delay(2000);

    // Turns left
    spinup_motors();
    set_motors(kilo_turn_left, kilo_straight_right/2);
    delay(5000);

    // Goes straight again
    spinup_motors();
    set_motors(kilo_straight_left, kilo_straight_right);
    delay(4000);

    // Turns right
    spinup_motors();
    set_motors(kilo_straight_left/2, kilo_turn_right);
    delay(5000);

    // Goes straight to get back to the race starting point
    spinup_motors();
    set_motors(kilo_straight_left, kilo_straight_right);
    delay(2000);
}

To make the kilobot move, we use the set_motors() function. Before calling it, we must call the spinup_motors() function to avoid static friction effects.

The two arguments of the set_motors() function indicate the power of each motor of the kilobot. Those values can go from 0 (off) to 255 (full speed). To take calibration into account, it is recommended to use the predefined values kilo_straight_left, kilo_straight_right, kilo_turn_left and kilo_turn_right rather than some raw numbers.

---

The main() function

We are almost done ! At this point, we only have to define the entry-point of our program : the main() function.

int main() {
    // Initializes hardware
    kilo_init();
    // Starts program
    kilo_start(setup, loop);

    return 0;
}

The main() function must always call kilo_init(), then kilo_start() in order to start the program.

---

We are done !

You can now admire your kilobot burn the tarmac ! Well, it might not be that impressive. The kilobots were probably not designed as racing machines. But fair enough, it at least made you learn the basics of programming for kilobots !

---