In the last few years, mobile robots are increasingly being used in natural outdoor terrain for applications such as forestry, mining, rescuing, precision farming, and planetary exploration. Future tasks will require robotic vehicles to travel over longer distances through challenging terrain, with limited human supervision. To accomplish this objective, a higher degree of mobility will be primarily required, ensuring, at the same time, the safety of the vehicle. In this paper, a robot with advanced mobility features is presented and its locomotion performance is evaluated, following an analytical approach. The proposed vehicle features an independently controlled 4-wheel-drive/4-wheel-steer architecture that allows the robot to perform maneuvers such as turn-on-the-spot and crab motion. It also employs a passive rocker-type suspension system, improving the ability to traverse uneven terrain, while ensuring good traction performance. An overview of modeling techniques for rover-like vehicles is introduced. First, a method for formulating a classical kinematic model of an articulated vehicle is presented. Next, a method for expressing a quasi-static model of forces acting on the robot is described. Note that quasi-static models are appropriate due to the relative low speed and acceleration of those vehicles. Two optimization methods are also proposed to control the rover's motion, minimizing slip and power consumption, respectively. These models are used to reproduce the behavior of the robot in typical obstacle-climbing scenarios, pointing to the advantages compared with conventional architectures.
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