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

3.2 Characterization of the Vibrations 42suddenly larger and irregular for high angular velocities (ω ∗ z > 30 degs ).First of all, it must be specified that the accelerometers are intentionally not mechanicallyisolated from the robot structural vibrations, therefore the frequency components found inthe recorded signals may derive, especially in the high frequency spectrum, from structuralvibrations which do not depend on the tire reaction forces and do not contribute to the largeamplitude vibrations which destabilize the robot. However, as the accelerations in (3.6)depend on both the robot acceleration and on the Roll and Pitch angles, we might think thatthe high frequency component derives from the robot platform accelerations, produced bythe tire reaction forces, while the low frequency component derives from the Roll and Pitchoscillations. The Roll and Pitch oscillations increase when, due to the type of ground andthe robot inertial properties, the frequencies deriving from the tire reaction forces get closerto the robot structural resonance frequency. In such a condition, when the robot oscillationsbecome relatively large, the high frequency components are mostly not affecting the signalsanymore. This could also explain the difference in the oscillation amplitude when running oncarpet with respect to concrete and tile. In fact, as the carpet is more rough and has a higherfriction coefficient than concrete and tile, the frequency of the vibrations coming from thetire/ground interaction forces might get closer to the resonance frequency for lower angularvelocities. Moreover, the fact that there are, usually, two low frequency components mayderives from two different resonance frequencies for the Roll and Pitch motion.In order to understand how the robot inertia contributes to large vibrations, the same testswere performed by using the robot platform without the laptop supporting structure. As therobot behavior and the acquired data qualitatively do not change between the concrete andthe tile floor, we will be considering only the data acquired on concrete and carpet. Similarlyto the previous case, some example graphs of the low-pass filtered data with their FFT areprovided in Appendix B. The graphs representing the average of the data amplitudes and theaverage of the three highest peak frequencies with respect to the angular velocity ω ∗ z and thetype of ground are also provided in Appendix B.By looking at the graphs depicted in Appendix B, we can claim that:• Large amplitude vibrations never appears.• Low frequency components nearly do not appear in the FFT of the data.• The peak frequencies seem to periodically increase when increasing the robot angular