Advance Modeling of a Skid-Steering Mobile Robot for Remote ...

6.2 Simulation Results 95vibrations at relatively high and low frequency. However, the model does not quantitativelyreproduce the expected large amplitude oscillations on the Roll and Pitch motion.• The value of λ max significantly affects the robot angular velocity, the lateral skid velocityand the frequency of the vibrations. In particular, the higher λ max is the lower the angularvelocity is (see the error ∆ω z in Figure 6.9(b)), the higher the lateral skid velocity is andthe lower the frequency of the vibrations is.By taking into account the last point, we can deduce that the value of λ max strictly characterizethe wheel/ground interaction and it might depend on both the ground and tire properties.Furthermore, in order to qualitatively and quantitatively evaluate the model with respect tothe amplitude and the frequency of the vibrations, we run the simulation for several values ofω z between 4 degsand 60 deg . The signals provided by the ¨Accelerometers ¨ block are sam-spled by a ¨Zero-Holder¨ block at 1 kHz and analyzed in the frequency domain by employingthe Matlab functions defined in Appendix A, as it was done for the real data acquired fromthe accelerometers (see Section 3.2). Some example graphs of the low-pass filtered datawith their FFT are provided in Appendix C. The graphs representing the average of the dataamplitudes and the average of the three highest peak frequencies with respect to the angularvelocity ω z and different values of λ max are also provided in Appendix C.Although it was not possible to carefully characterize the model behavior and the contributionof the parameter λ max , there are some features we can extract. In particular, by lookingat the graphs depicted in Appendix C, the main features can be listed as follows:• For λ max = 1, there is only one frequency component which increases when increasingthe robot angular velocity.• For λ max > 1, there are usually two frequency components, respectively at ¨low¨ and¨high¨ frequency.• For λ max= 10 −1 , 10 −2 , the main peak frequency is the at same frequency for all thethree accelerometer axes, i.e. a x , a y , a z . Such a peak frequency seems to increase withthe angular velocity up to 20 Hz, for relatively low angular velocities (ω z < 20), while itremains almost constant at ¨low¨ frequency for relatively high angular velocities (ω z >20).