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Tham khảo tài liệu 'robotics part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Wheeled Mobile Robots 163 FIGURE 4.7 for in the conclusions of the mathematical study and that other predictions are subsequently verified by experiment. A typical situation would be that the set of conclusions of the mathematical theory contains some which seem to agree and some which seem to disagree with the outcomes of experiments. In such a case one has to examine every step of the process again. It usually happens that the model-building process precedes through several iterations each a refinement of the preceding until finally an acceptable one is found. Pictorially we can represent this process as in Figure 4.7. The solid lines in the figure indicate the process of building developing and testing a mathematical model as we have outlined it above. The dashed line is used to indicate an abbreviated version of this process which is often used in practice. 4.3.2 Kinematic Constraints Figures 4.8 and 4.9 show how the instantaneous center of rotation is derived from the robot s pose in the case of a car-like mobile robot or wheel velocities in the case of a differentially driven robot . The magnitude of the instantaneous rotation is in both cases determined by the magnitudes of the wheel speeds the distance between the instantaneous center of rotation and the 164 Robotics FIGURE 4.8 Instantaneous center of rotation icr for a car-like robot. wheel center points is called the steer radius 18 or instantaneous rotation radius. Figures 4.8 and 4.9 and some simple trigonometry show that 1 ir tan ơ r s d Ur ui _ . 2 ur-U for a car-like robot for a differentially driven robot 4.1 with the wheelbase of the car-like robot 18 i.e. the distance between the points where both wheels contact the ground the steer angle the distance between the wheels of the differentially driven robot and its wheel velocities. FIGURE 4.9 Instantaneous center of rotation for a differentially driven robot. Wheeled Mobile Robots 165 Differentially driven robots have two instantaneous degrees of .