Webots User Guide

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Foreword

Thanks

1.Installing Webots

2.Upgrading from Webots 2

3.Getting Started with Webots

4.Tutorial: Modelling and simulating your robot

5.Robot and Supervisor Controllers

6.Tutorial: Using the KheperaTM robot

7.ALife Contest

     

7.2 Rules

7.2.1 Subject

Two robots are roaming a maze-like environment (see figure 7.1), looking for energy. Energy is provided by chargers (see figure 7.2). However, chargers are scattered all around the environment and it is not so easy for robots to find them. Moreover, once used by a robot, a charger will be unavailable for a while (see figure 7.3). Hence, the robot will have to go away and look for another charger. A robot will die if it fails finding an available charger before it runs out of energy. Then, the remaining robot will be declared the winner of the match.

alife_world

Figure 7.1: The world used in the contest

alife_full_charger

Figure 7.2: A charger full of energy

alife_empty_charger

Figure 7.3: An empty charger

7.2.2 Robot Capabilities

All robots have the same capabilities. They are based on a model of Khepera equipped with a K6300 color matrix vision turret. Hence each robot has a differential wheels basis with incremental encoders, eight infra-red sensors for light and distance measurement, and a color matrix camera plugged on the top of the robot, looking in front. The resolution of this camera was scaled down to 80x60 pixels with a color depth of 32 bits. As you may have already understood, analysing the camera image is a crucial issue in developing an efficient robot controller.

7.2.3 Programming Language

For the contest, the robots can be programmed in Java only. This ensures that the binaries carry no viruses or cheating systems. Hence, the executables files (.class files) can be easily shared amongst competitors without disclosing source code. Beware, that very good Java decompilers exists and that it may be possible (although difficult and tricky) for a cheating competitors to restore your code from your .class. If we encounter such problems, we will disable the Java binary code sharing.

They is no limit on the computation time a robot can use. However, since the simulator runs approximately in real time without any synchronization with the robots, robots performing extensive computations may miss some sensor information or react too late in some critical situations.

7.2.4 Scoring Rule

Once submitted on the web site, a robot is assigned a score of 10 points. Then, it will perform continuously a number of matches against other robots until its score reaches 0. At that point the robot will be eliminated from the contest. Scores are floating point values. When a robot wins a match it draws points from its opponent. The amount of points transfered from the loser to the winner is computed as follow:

1 + abs(winner_score - loser_score)/winner_score

If the amount of points to be transfered is higher than the score of the loser, then the loser is eliminated from the competition and the winner only receives the score of the looser, no more.

It is always possible to introduce a new version of an existing robot controller, by simply uploading the versions of the .class files, erasing any previous ones. When a new version of a robot controller is introduced in the contest, its score remains unchanged. The next matches are run using the new version.

7.2.5 Schedule

The contest started on July 1st 2002. From this date, competitors could download all the contest material and develop their robot controller. Matches between resulting controllers are held continuously from the middle of the summer until the end of the competition, on May 1st 2003. It is possible to enter the contest at any time before May 1st, 2003.

7.2.6 Prize

The winner of the contest will be the robot ranked at first position on May 1st, 2003. The authors of this robot will receive a Khepera II robot and a Webots PRO package (see figure 7.4). Prizes for the second and third position are not yet determined.

alife_prize

Figure 7.4: First prize: a Khepera II robot and a Webots PRO package.

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