November 2009 to February 2010

Ludovic Apvrille

Mindstorms NXT(TM) robots are robots made of a main unit and a set of senors and actuators. They are sold by Lego for a few years now. Many very tricky things have been made using the standard kit (see for example that publication). You may also visuliaze interesting videos on youtube,  and for example a car factory, a walking dog, a scorpion, a forklift truck, the "holononic drive", and a rubik's cube solver.

The project you ought to do is not as complex as some aforementioned systems, but yet, it requires to spend quite a lot of programming / exploration time on the robot and its interfaces (sensors, actuators).

• Two robots are placed in an arena. The arena is 1 meter large and 2 meters long, and protected on all sides with a fence high of 10 cm. This arena is divided in two squares of equal size ("area of robot 1", "area of robot 2"), defining each robot camp.

• A red ball is placed right in the middle of the arena.  The red ball which is used is the one provided with the robot kit.

• The two robots are started at the same time from a pre-defined initial location ("starting zone of robot 1", "starting zone of robot 2"). Inside the corresponding location, each team may place its robot as desired.

• First game phase: robots must try to grab the ball. Since the ball may be moved by robots (but not thrown away from the arena!), you shall not assumed that the ball is always at its initial location.

• Once the ball has been grabbed by a robot, that robot must signal to the other robot that it has grabbed the ball, using its bluetooth interface. (The robot which has grabbed the ball scores one point). Also, it must play a sound: "I've got the ball".

• Then begins the second game phase:  the robot having the ball - the attacking robot - has 1 minute at most to bring the ball (and release it) along the "scoring fence" of its opponent area. Of course, the other robot - the defending robot - shall try to prevent the attacking robot  from releasing the ball. By releasing the ball, we mean that the ball must be at most at 5 cms from the fence, and not hold by the robot anymore. The ball must not be thrown, but put on the floor so that its does not move. By "prevent", we mean that the defending robot shall try to act so as to modify the attacking robot trajectory by pushing it for example, or trying to raise it so as its wheels are not longer functional, etc. Of course, "prevent" does not mean "destroy" or "damage" i.e. no "destrutive weapons" are allowed, e.g. sending chlorhydric acid to the other robot is forbidden. If the attacking robot manages to release the ball in the right place, it scores two points. Note that after that one minute phase, both robots must deactivate themselves automatically. Also, when the attacking robot scores, it must inform the defending robot - again using its bluetooth interface -, and both robots must automatically stop.

• Then, another first game phase is played between the two same robots, until the 5 minutes have elapsed: The ball is positionned again in the middle of the field, except if a robot scored during previous round: in that case, the ball is placed on the line between the two opponents'area, at a location decided by the team not scoring at previous step.

• At the end, the winning robot is the one with the highest score.

• Grab the ball when it is positioned in the middle of the arena.
• Grab the ball when it is positioned on the middle line.
• Grab the ball when it is at a random position of the arena.

Pictures and video of this first competition are there (from a Microsoft Windows explorer): \\karma.eurecom.fr\public\COMMUNICATION\PHOTOTHEQUE\robot_cours_Apvrille

• The robot must be contained in a cube of 30 cm maximum on each dimension, part from the height, to support the compass sensor.

• It may change its shape (by deploying elements, or withdrawing some) during game phases, but it must remain all the time in the aforementioned dimensions.

• Your robot is not allowed to lose parts on purpose during the game.

• It is forbidden to send orders - remotely or not - to your robot while it is playing: it must be autonomous as soon as the game starts, and until it ends.

• Start experimenting with NXT robots, especially with the default graphical environment. Try to make different robots so as to evaluate how sensors work, and more specifically, the precision of those sensors i.e. how reliable is the information they provide.

• Then, be imaginative about the structure of your robot...

• ... but do not invent very complicated algorithms that you may never finish to implement. At first, experiment with basic ideas, then improve your robot's algorithms if we've got some time left.

• You will not be able to make a working robot if you do not split the work inside of the group: in a group, each member shall work on different elements of the project. Otherwise, you won't reach the objectives.

• The "LabView" environment provided by LEGO Mindstorms might be quite an important limitation when programming complex algorithms. I suggest to use other programming environments, and more specifically the "Not eXactly C" (NXC) one. More information on NXC are provided below.

• There are two deadlines:
• The first one the 17th of December, 2009, before the lecture on OS starts: the draft of your web site must be ready, and "the seek for the ball and grab the ball" stage must be working (the second game phase will not be experimented). First competitions will be organized during the second part of the OS lecture. 
• The second deadline is the 28th of January, 2010, 23:59. The web site shall be ready, and your NXT robot fully functional i.e. it shall implement the two phases: a draft of the source code shall be on the web site, as well as algorithms. You have the right to modify your source code after that date, until the last deadline. 
• The last deadline is the 17th of February. Your final source code shall be on the website. Competitions will be organized the 17th of February in the morning. I will also interview each member of the group, so as to understand the contribution of each member.

• Your report consist in  a website. The web site 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 game stages. Don't provide a 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.
• 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.

• Group #1: Edward John Fulda, Bachir Chraibi, Wenting Li, Yara Kazma (4 students)
• Group #2: Corentin Mauran, Matthias Hernandez, Quentin Marchal, Thomas Kahn, Alexis Hafner (5 students)
• Group #3: Maria Giovanna Cucca, Pietro Pezzolla, Adriano di Martino, Francesco Albanese and Yao Liu (5 students)
• Group #4: Olivier Bouvet, Nicolas Dumont, Léo Goffic, Louis-Marie de Penfentenyo (4 students)

• Robots may be borrowed from Marie-Laure Victorin, at the Computing Department Secretary's. Please, take care not to loose parts, especially cables and sensors.
• Batteries may be borrowed from Laurent Castledine. When they are discharged, you may pick up a new set of charged batteries from his office.

• It is free
• You don't need to change the firmware of the NXT robot i.e. nothing has to be changed on the robot to be able to use NXC.
• NXC is a language which is very close to the C language: you don't need to learn a new language. There are several tutorials on the web site, as well as a reference guide.

• I have first installed the package provided in "beta releases" (menu on the left, on the web site).

• Then, I have uncompress it, installed it in /Applications/nxt

• I have modified my .bashrc file so as to be able to execute NXC applications from a shell. More precisely, I have added the following line to my .bashrc file:

• I have downloaded the tutorial samples code, and I have unzipped it, let say in /Users/ludovic.apvrille/code

• I have compiled the "5_light.nxc" code as follows, from a terminal:

• I have plugged my NXT robot on a USB port, and switched it on. Then, I have run the following command: