Seite - 198 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

Toavoidunintendedmovementsof thekingpin joints, theGazebosreal timeupdatehas tobe2000Hz and themaximum step size0.0005s. The following three improvements would increase the accuracy of the simulation. Firstly, detailed measurements should be taken to replace the wheels approximated friction parameter. Secondly, damping should be added to the vehicle. Finally, the front wheels should be powered and equipped withadifferential. 7. Results Two tests are carried out to quantify the accuracy of the real and the simulated robots motion. For thefirst test, a semicirclewith themaximumsteeringangleandavelocityof0.1m/swasdriven. The low speed used during the test allows for errors stemming from wheel slipping and centrifugal force to be ignored. The motion model represents the motion commands in this test, so it can be used as a reference. The radius of the semicircle driven by the real car is 5cmbigger than the reference. This is caused by the unsteady steering of the RC-race car. The simulated car drives a trajectory differing fromacircle. During thewhole test, thepositionsof the realand thesimulatedcararecoveredby the covarianceellipse. InFigure5a the test results are shown. For the second test, a straight linewas drivenwith avelocity of0.1m/s, basedon themotion models response. The real car stops4.5cmbefore the reference, because of inaccuracies in the measurement of the wheel size. The simulated car stops 1.8cmbehind the reference. The reason for this deviation is that unlike Gazebo, the motion model does not regard the kinetic energy of the vehicle. Again, the covarianceellipsecovers thepositionof the realand thesimulatedvehicle. The test resultsareshown inFigure5b. To increase the accuracy of the motion model, two improvements can be made. Firstly, the number of updates can be increased to downsize the time steps. Secondly, the kinetic energy of the vehicle shouldbeconsideredby thevelocitymotion model. MotionModel RealCar SimulatesCar Covariance (a) MotionModel RealCar SimulatesCar Covariance (b) Figure5: Comparison of trajectory and visualisation of the (a) rotational and (b) the straight behavior of thecovarianceellipse. 198