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

6.2 Simulation Results 96• For λ max = 10 −3 , 10 −4 , 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).• For λ max = 1, the amplitude of the vibrations linearly increases with the angular velocityfor a y , while it remains almost constant at relatively low value for a x , a z .• For λ max = 10 −1 , 10 −2 , the amplitude of the vibrations linearly increases and then remainsalmost constant, respectively at low (ω z < 20) and high (ω z > 20) angularvelocity for a y , a x , while it remains almost constant at relatively low value for a z .• For λ max = 10 −3 , 10 −4 , the amplitude of the vibrations remains almost constant at relativelyhigh and low value respectively for a y and a x a z .• For all the tested cases, the amplitude of the vibrations is much smaller than the amplitudesof the real robot vibrations acquired from the accelerometers.Finally, we can claim that the overall model qualitatively reproduces the frequencies butnot the amplitudes of the real vibrations measured by the accelerometers. In particular, thevalue of λ max , which allows the model to be ¨closer¨ to the real system behavior, seems tobe of an order of magnitude of 10 −1 , 10 −2 . However, by comparing the graphs in AppendixB and C and taking into account the considerations made in Section 3.2, we notice that themodel does not quantitatively reproduce the amplitudes and frequencies of the real robotvibrations yet. The reasons of such a discrepancy might rely on the lack of an identificationof λ max or on the irregularities of the ground surface.Thus, we conclude saying that, in order to validate the model also from a quantitative pointof view, an accurate identification/estimation of the maximum wheel slip λ max is needed. Ifafter such identification the model is still inaccurate for our needs, we can either try to modelthe irregularities of the ground surface or propose another model.