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

3.2 Characterization of the Vibrations 37its acceleration along its axis.3.2 Characterization of the VibrationsThe aim of this section is to provide a qualitative and quantitative idea about the vibrationswhich occur while the robot is turning (ω L ω R ). First of all, different qualitativetests has been done by running the robot at different angular velocities on different types ofground. The tests has been also done by modifying the robot’s structure, therefore changingits dynamics configuration. In particular, the robot has been run with and without the aluminumframe and the laptop, with different types of tire and even with two cubes of woodreplacing two wheels on the same side. Moreover, to check the importance of the robot inertia,a long plastic pale with two weights attached to its extremes was fixed to the robot alongits principal axes. After several tests, we could clearly claim that the main cause of the robotvibrations is the complex behavior of the lateral reaction forces, due to the tire dynamics andthe complex tire/ground interaction, and their interaction with each other. In fact, when wereplace two wheels with cubes of wood, large vibrations never appear independently fromthe robot’s structure. Conversely, when the four wheels are mounted on the robot, the vibrationsdo not appear while running the robot’s platform, but they become relevant when thealuminum frame is fastened on it and they increase when increasing the robot weight andinertia along the x and y axis.In order to have also a quantitative idea, the vibrations are measured by acquiring the datafrom the accelerometers fixing the wood-cube to the robot in different locations, whileswiveling the robot in place with different angular velocities (v ∗ x = 0, ω ∗ z 0). The dataare also acquired by running the robot on all the types of floor in the School of Engineeringat RWU, i.e. carpet for the rooms, tile for the corridors and concrete for the laboratories.The relation between the acceleration a = [a x a y a z ] T measured from the three accelerometersand the robot acceleration ˙V, when the wood-cube is fixed to the robot at the positionp a with respect to the robot CoM, can be obtained by computing the linear velocity of thewood-cube from the robot velocity, differentiating it with respect to time and adding the gravitycontribution. The linear velocity v a can be computed by applying the Plücker transformfor spatial velocity vectors [18], [19] to the robot twist V: