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Evolutionary Design of a Control Architecture for Soccer-Playing Robots  205
                           2.2 Experimental Analysis

                           The various effects of slip and friction are experimentally measured in two
                           stages. The first stage is dedicated to the determination of the robot’s orien-
                           tation error ∆α. To this end, the robot is located in the center of a circle with
                           1m in radius. The wheel speeds are set as follows:

                                              r 1 = v · sin(π − 60).
                                              r 2 = v · sin(π + 60).                        (1)
                                              r 3 = v · sin(π + 180) = −r 1 − r 2 .
                           with r i=1...3 denoting the rotation speed of wheel i and v denoting the robot’s
                           center speed. In an ideal case, these speed settings would make the robot
                           move in a straight line. In the experiment, the robot moves 1 m. After moving a
                           distance with a moderate speed, the robot’s orientation offset ∆α is measured
                           by using the camera and the image processing system. Fig. 5 illustrates this
                           procedure.
                              Stage two repeats the experiments of the first stage. However, the rear
                           wheel is adjusted by hand such that the robot’s orientation does not change
                           while moving. This stage then measures the drift ∆ϕ, as illustrated in Fig. 6.


                               5
                               4
                               3 2
                             correction value  −1 1 0


                              −2
                              −3
                              −4
                              −5
                              −6  0      90        180       270     360
                                            angle j
                           Fig. 5. Turning behavior of the robot due to internal rotation and its correction
                           with an additional correction value of the rear wheel 1 for different angles ϕ
                             15
                                   angular drift j
                             10

                              5                                                 j
                              0                                                 j'
                             −5
                            −10                                                    1m
                                         90       180       270     360
                                            angle j
                              Fig. 6. Drift values ∆ϕ for different angels ϕ with rotation compensation
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