General information

Project of Fall 2018: "Basketball game"

Mindstorms NXT(TM)/EV3 robots are robots made of a main unit and a set of sensors and actuators. They have been sold by Lego for several few years now, starting with the NXT version, and now with the ev3 version. Many very elaborate designs have been made using the standard kit (see for example "Mindstorms: Not just a kid's toy"). You may also watch interesting videos on youtube, such as a breakfast machine, marble conveyor, a car factory, a walking dog, a scorpion, a forklift truck, the "holononic drive", a rubik's cube solver, a printer, and a sumo game. You can also find some other nice systems on battlebricks.

The project you will work on is not as complex as some aforementioned systems, yet it requires spending quite a lot of design and programming time on the robot and its interfaces (sensors, actuators).
Test your robot, motors, and sensors as soon as possible! We may be able to repair/order parts with a few weeks notice, but there is very little we can do the day before the competition.

Project description

The robot you have to build shall be the winner of a basket ball game. This section includes a description of the game and then a specification of the robot.

Note that the rules might evolve during the next weeks, along with the communication protocol until the final competition. I will always inform you whenever a rule evolves.

General description

The main objective of the game is to score points by sending balls into a basket. Each time you score points, you should inform the server. The server will inform the two robots about the current game score. A game is as follows.
  • Two robots compete together in the same stadium. A side of the stadium is dedicated to one robot, and each robot starts in its own starting area. If during a game a robot enters at least one time the opponent's side, then the robot looses one point. "entering" means that at least a part of the robot touched the floor over the black line, e.g. part of a wheel.

  • First, a game server is started. Each playing robot should register to the server. The id of the robot in the server corresponds to the id of the student group, see the group section

  • Robots have 4 minutes at most - i.e. as soon as the two robots are stuck or as soon as no balls are available any more, the games ends - to score points by sending balls into a basket located as indicated below. The overall game area is delimited by a wooden fence on the four sides (see figure below).

  • Robots can contain up to two balls when the game starts. Four other balls are randomly placed in the stadium by your favourite professor. If the robot cannot contain two balls, then the corresponding team can put the balls not fitting in the robot in the stadium at the position of their choice.

  • When a robot successfully sends a ball from the "front area" to its corresponding basket, it scores 1 point. 3 points are given when the shot was performed from the "far area" i.e. no part of the robots were touching the floor in the "front area". When a robot thinks his shoot was successfull, it should inform the server via bluetooth. A specific bluetooth communication protocol is defined in the project repository. This repository also contains the code of the game server, and example code for ev3 robots. The server is started and configured before each game starts. The protocol contains a "CUSTOM" message that you may use between robots in order to send additional information.

  • Robots also have the right to release obstacles, e.g. throwing an obstacle into the opponent's side.

  • The robot can be freely re-programmed between game rounds, but you don't have the right to add/remove lego bricks - apart from the obstacles -, sensors, etc.

Tournaments will be organized, and medals (master, diamond, platinum, gold, silver and bronze medals) will be given to robots according to their ranking. The ranking is first determined with the score and the number of victories.


The stadium is explained in the following picture.
this is a PNG
Specification of the small stadium. This stadium has a wooden fence. 1 point is given when scoring from the front area, 3 points is given when scoring from outside of the front area. The basket itself is specified in this document. Balls have a diameter of around 5.5cm.

Specification of the robot

  • The robot must be contained in a cube of 35 cm maximum on each dimension at start-up.

  • Robots can use up to four sensors and up to four engines. You are free to use the sensors you want to among the following ones: touch sensor, light sensor, color sensor, ultrasonic sensor (i.e., distance sensor), compass sensor, gyroscope sensor, magnetic sensor.

  • The robot must contain a flag, on which the number of your group is clearly readable from at least two sides of your robot. The flag dimension is at most 10x10cm. It may also contain a logo, a drawing, and the name of the robot.

  • The communication protocol between robots (bluetooth) will be given (you don't have to specify it). Basically, robots communicate to a server (and possibly other robots).

  • A robot may change its shape (by deploying elements, or withdrawing them) during game phases, but it should fit in a 35cm cube at the start of the game.

  • Destructive weapons are NOT allowed. For your information, a EMP can be constructed for ~300 dollars as shown here.

  • It is forbidden to send orders - remotely or not - to your robot while it is playing, apart from the BT communication with the server: it must be fully autonomous as soon as the game starts, and until it ends. Trying to hijack BT messages, or other kinds of attacks is not allowed.

Competitions and reports

There are two "competitions", as described after. Your project grade takes into account the two competitions (the one in December, the one in January).
  1. The 18th of December, 2018: your website should be started with at least the name of your robot (I don't expect more in the website for this deadline), and your robot should be able to explore the small arena, and to avoid bumping into obstacles. The six following tests will be performed alone in the stadium. Tests are used to test "basic" functions in ordert o understand how well their work. They are not taken into account for the final grade, apart if the final competition fails. Test #1 and #2 are useless if test #3 is perfectly validated.

    • Test #1. Be able to drop a ball in the basket.
    • Test #2. Be able to send a ball in the basket from the front area.
    • Test #3. Be able to send in a reliable way a ball into the basket from the distant area.
    • Test #4. Be able to find a ball and pick it up. The test is performed with a ball placed at a selected position at least at 15cm from the robot.
    • Test #5. Be able to find a randomly placed ball and stay in the correct side.
    • Test #6. Be able to connect to the server and inform the server when a ball is scored.

  2. The 22th of January, 2019: final competition. For the final competition, the website must be fully completed. Also, during the final competition, I may interview each member of the group, so as to understand the contribution of each group member.

Your report consists of a website. The website shall contain the following information:
  • Description of the architecture of the robot: sensors and actuators, etc. Pictures of your robot on the web site would be appreciated.

  • Algorithms used for the two most important points: strategy to drop or throw balls, to find and pick up balls, competition with other robots, etc. Don't provide source code here, just try to describe the algorithms using a pseudo C language. Also, do comment those algorithms, and explain why you think they are efficient.

  • Source code, and instructions on how to use that source code: how to compile it, how to download it on the robot, and how to start the robot. To protect you work, you can set a password to access to the code, but make sure to give us access in order to grade it (e.g., private git repository). You could even put a fake code on your website until the very last moment ;-). I strongly advise you to rely on a versioning system (svn, git, hg) to work on the code. Also, frequently backup your code.

  • Videos / pictures of your robot in action [we may provide you with cameras and video recorders if necessary].

  • How you have worked in the group, i.e., who made what. Be clear about that. Each member of groups will get an individual grade. All members of a team must contribute to the source code. You source code must clearly indicate, with comments, who programmed which function.


(Current total: 8 groups of 4, 3 groups of 3. Remaining: 0 groups of 4, 0 group of 3)
(The group leader is listed first. BT address starting with 00:17).
  1. Name of the members, name of robot and link to website, BT address.

  2. Yasmine BENNANI, Sami AAZMI, Antonin GODARD. LEGOLas

  3. Arthur DION, Antoine GALLET, Paul MONNIOT. RobotJames

  4. Fausto CHIATANTE, Alessandro Tempia CALVINO, Giulio ROGGERO, Alberto ANSELMO. Baffo

  5. Simone Alessandro CHIABERTO, Sebastian YLANDER MIKKELSEN, Pietro MAMBELLI, Philip GERTZELL. MJ23

  6. Yohann Jacob SANDVIK, Kaja GAUSDAL, Embla Trasti BYGLAND, Trym SNELTVEDT. Kob-E

  7. Javier ERREA, Ivan EROSHKIN, Manuel Alejandro QUERO ORTEGA, Niki PAPAGORA. El Stupido

  8. Nour Karam RABEH, Safa REJEB, Louis-André AGROFOGLIO. Drunken

  9. Thomas DEFARD, Colombe LOPEZ, Jakob FITTLER, Mailys DESVIGNES. Fittler

  10. Corentin RAFFLIN, Tom BENHAM, Bastien ZIMMERMANN, Alex BOURG. Legogoat

  11. Dhiaeddine ALIOUI, Aicha MHEDHBI, Bechir BOUALI, Prince AMANKWAH. Scorpion

  12. Julie BONNASSIEUX, Pauline TRONCY, Abbe AHMED-KHALIFA, Jordan MEALLIER. Bascat

How do I borrow a robot?

There will be eight groups of 4 students, and three groups of 3 students. Please, take care not to lose parts, especially cables and sensors. Also, a microsd card comes with the robot. The procedure to borrow a robot is as follows:
  1. Make a group of 4 (or 3), and decide on a group leader.
  2. The group leader sends me an email with the list of students of the group. List of: first_name, LAST_NAME, email. The leader shall be the first student in the list.
  3. I will validate the group. If the group is not validated for some reason I will provide, go back to stage 1. Otherwise, go to next step. Note that I validate groups with a First Come First Served policy (Date of email sent).
  4. Once I've answered your group with "validated", the group leader can go to Franck Heurtematte's office, in the IT Department. You will be granted an ev3 box. Only the group leader has the right to enter in the office of Mr Heurtematte, and only during the morning or the afternoon breaks (do not go during lunch break).

Access to stadiums

  • Small stadium. The small stadium is located in room 52. You are free to use it whenever you want.


For the ev3 system, the idea is to flash on the provided SDcard a Debian GNU/Linux system. Then, you will be able to use the development language of your choice (C, python, etc.). But we ask you to develop in C.

Installing Linux on ev3

All information to install Linux on your ev3 is given here. This page also explains how to connect to your ev3 via the usb cable, bluetooth, and ssh.

Using and programming ev3

  • Connect to the EV3 from ssh
  • If you have difficulties to connect to your robot via BT ou USB, please contact us. Another option is also to use a WiFi dongle plugged into the USB port of the ev3. The Edimax N150 nano works fine, but we don't provide one (FYI: it costs around 8 euros).
    Once your robot has access to Internet, it should display its IP address in the upper left corner of its display (let's assume it is Then, you can try to ssh to the robot (the default password is maker):
    $ ssh robot@
    The robot user is a sudoer, i.e. it can execute commands with root privileges when using the command sudo first.

  • Now, update the robot with the latest packages
  • $ sudo apt-get update&&sudo apt-get upgrade

  • Install extra packages you will need for the project:
  • $ sudo apt-get install gcc make libbluetooth-dev

  • You are now ready to compile a basic example, and to run it. To do so, you first need to install the development environment on the robot:
  • $ GIT_SSL_NO_VERIFY=true git clone https://github.com/in4lio/ev3dev-c.git
    $ cd ~/ev3dev-c/source/ev3
    $ make
    $ sudo make install

  • Now, you need to get the example. The tester file runs all 3 motors, then tests the color, touch, sonar, and compass sensors, and is provided on the project git. You can either clone the git with the code on the robot, or on your host computer.
  • $ GIT_SSL_NO_VERIFY=true git clone https://gitlab.eurecom.fr/ludovic.apvrille/OS_Robot_Project_Fall2018.git
    $ cd OS_Robot_Project_Fall2018/
    If you are on your host computer, you then need to copy the example files to the robot:
    $ scp tester.c Makefile robot@

  • Then, on the robot, you can compile the example main file, and then run it. You need tachos and sensors to be connected to the brick if you want the program to correctly execute.
  • To compile:
    $ gcc -I./ev3dev-c/source/ev3 -O2 -std=gnu99 -W -Wall -Wno-comment -c tester.c -o tester.o
    $ gcc tester.o -Wall -lm -lev3dev-c -o tester
    $ make
    To run the code:
    $ ./tester
    $ make run

Other examples

  • Sample code is also provided in the ev3c-master repository. Samples of how to control the motors and sensors are included in tester.c. The Ultrasonic Sensor is described here.

  • If your compass sensor does not correctly work with the test_sensor program, we provide a code specific to the use of this sensor. Use the "i2c" target of the provided Makefile to compile the file.

  • Other examples can be downloaded from the ev3dev C library here. Examples are provided in eg/tacho and eg/sensor.

  • rfcomm-client.c is an example of how to communicate with the server over bluetooth. Compile with gcc rfcomm-client.c -o rfcomm-client -lbluetooth.

  • If you can't get your robot working, bring it along to course staff.

Cross compilation


You may want to compile your source code on your laptop, e.g. to check the syntax of your code or to speed up the compilation process. Cross-compilation for ev3 is available as an ev3 docker image. Here is what I've made to make this work on my Debian GNU/Linux computer:
  1. I have first installed docker, created a docker group, added myself to the docker group, and started the docker service. Installing docker may require more than a simple apt-get, so please refer to the document of your OS, e.g. for the one for ubuntu
  2. $ sudo apt-get install docker-engine
    $ sudo groupadd docker
    $ sudo gpasswd -a ${USER} docker
    $ sudo service docker start
    You may have to log-out for the group modification to be effective.
  3. Then, I have installed the ev3 docker image:
  4. $ docker pull ev3dev/debian-jessie-armel-cross:latest
  5. Once done, I've created a helloworld in C:
  6. $ cat > /tmp/hello.c
    int main(int argc, const char *argv[])
        printf("OS is fantastic!!\n");
        return 0;
    (do "CTRL D" at the end of this command).
  7. I've compiled the file using the cross compiler provided within the docker image, and tested the generated file. The following command assumes that hello.c is located in /tmp on your host system (but you can place it wherever you want: update the following command accordingly). The following instructions are the one that I have used on my debian/jessie GNU/Linux PC.
  8. $ docker run -e LOCAL_USER_ID=`id -u $USER`  --rm -it -v /tmp:/src -w /src ev3dev/debian-jessie-cross
    [Shell in container]$ cd src
    [Shell in container]$ arm-linux-gnueabi-gcc -o hello hello.c
    Then, if you want to execute the generated ARM executable, you first need to install the ARM emulation environment. Then, you can execute "hello":
    $ sudo apt-get install qemu-user-static
    [Shell in container]$ ./hello
    OS is fantastic!!
For handling the compilation for your ev3, you need to make additional stages (thanks to Paolo!):
  1. Tag the docker image:
  2. $ docker tag ev3dev/debian-jessie-cross ev3cc
  3. Install ev3 lib, put them in the project directory, and start the docker image:
  4. $ git clone https://github.com/in4lio/ev3dev-c
    $ docker run --rm -it -h ev3 -v PATH/TO/PROJECT/:/src -w /src ev3cc /bin/bash
  5. In the container, run the following commands:
  6. [Shell in container]$ cd ev3dev-c/source/ev3/&&make&&sudo make install&&make shared&&sudo make shared-install
    In the Makefile for compiling your code, do not forget to substitute “gcc” with "arm-linux-gnueabi-gcc”. For running your project, add "export LD_LIBRARY_PATH=~/ev3dev-c/lib”in the Makefile.

Another way to do

(Way suggested by Fredrik Flornes Ellertsen. Note: on our side, for the tester.c file, we had to put the exact location of included files such as ev3.h. And also we had to remove the lines that use 'ev3_brick_addr', which the compiler cannot understand)

This has been tested on native Ubuntu 17.04 and on Windows using the Windows Subsystem for Linux.
  1. In an empty folder (here called robot_code/) on your computer, clone the ev3dev repository:
  2. $ git clone https://github.com/in4lio/ev3dev-cs
  3. Install the cross compiler (source: https://www.acmesystems.it/arm9_toolchain):
  4. $ sudo apt-get install gcc-arm-linux-gnueabi
  5. In order to compile code that links to the ev3dev-c and/or bluetooth libraries, we need to use the robot's own versions of these libraries: libbluetooth.a and libev3dev-c.a. By linking statically we eliminate the need to install anything on the robot itself. Place these files in robot_code/libraries.

  6. Create a Makefile to simplify the compilation process. The following example Makefile expects the project to be organized like illustrated below, but will naturally depend on the group's project:
  7. 	robot_code/
    Running 'make' in the robot_code/ directory should yield an executable called 'main' in the same directory. Using a file transfer tool like scp, copy this file to the robot and run it.

Competitions results

First tests, December the 18th, 2018

Final competition, January the 22th, 2019

Points and evaluation criteria could be updated during competition to better reflect the capacities of robots.

    to come :-)