Robot Behaviors

Exploring the T-Maze: Evolving Learning-Like Robot Behaviors using CTRNNs


3 Experiment 1: Simple T-Maze


In the first experiment a robot has to navigate a simple T-maze (fig. 2). The experiment is carried out in a realistic simulation of the Khepera robot (fig. 1(a)) based on sensor sampling [6] and adding 5% uniform noise to the sampled values. Initially the robot is positioned as shown in figure 2, and the task is to find and stay on the black reward-zone which can be positioned in either the left or the right arm of the maze. The position of the reward-zone stays fixed during each epoch. The robot is tested for 4 epochs of 5 trials each - two epochs with the reward-zone in each arm of the maze. The neural network controlling the robot is initialized (by setting the state of each neuron to zero) at the beginning

of each epoch but not between trials within the same epoch. This means that the robot can potentially build up and store information in the dynamic state of the network between trials within the same epoch. The optimal behavior of the robot in this environment is to use the first trial of each epoch to locate and “remember” the position of the reward-zone, and thereafter move directly towards it for the remaining trials of the epoch. To put additional evolutionary pressure on this behavior, the number of available sensory-motor steps is 360 in the first trial of each epoch and only 180 in the remaining 4 trials. Given the size of the maze this means that the robot only has time to explore the whole maze during the first trial of each epoch. In addition a poison-zone (white square in figure 4(b)) is positioned opposite of the reward-zone in the last 4 but not the first trial of each epoch. An individual is immediately killed if it steps over the poison-zone. The fitness function is simply the sum of trials an

individual ends its life inside the reward-zone. Since each individual is tested for a total of 20 trials the maximal possible fitness is 20. Notice that there is no direct pressure on evolving fast moving robots given this fitness function. This is however compensated by the fact that the number of steps in each trial is limited and has been adjusted to fit the size of the environment.

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Amazon Books
Creative Projects with LEGO MindstormsCreative Projects with LEGO Mindstorms by Benjamin Erwin
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A good place to start, especially for kids, with Lego Mindstorms
RobotProgramming : A Practical Guide to Behavior-BasedRobotics A Practical Guide to Behavior-Based Robotics by Joe Jones
Buy new: $20.67 / Used from: $15.13
Very good for programming not so much behavior as control. Language and controller agnostic


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