A Kinematical and Dynamical Analysis of a Quadruped Robot

Abstract

In general, legged locomotion requires higher degrees of freedom and therefore greater mechanical complexity than wheeled locomotion. Wheeled robots are simple in general, and more efficient than legged locomotion on flat surfaces. Yet as the surface turns softer, wheeled locomotion becomes inefficient due to rolling friction. Furthermore, in some cases, wheeled robots are unable to overcome small obstacles. On the other hand, legged robots are more easily adaptable to different kinds of terrains due to the fact that only a set of point contacts is required; thus, the quality of the ground between those points does not matter as long as the robot can maintain appropriate ground clearance. Legged robots appear as the sole means of providing locomotion in highly unstructured environments. However, they cannot traverse every type of uneven terrain because they are of limited dimensions. Hence, if there are terrain irregularities such as a crevasse wider than the maximum horizontal leg reach or a cliff of depth greater than the maximum vertical leg reach, then the machine is prevented frommaking any progress. This limitation, however, can be overcome by providing the machine with the capability of attaching its feet to the terrain. Moreover, machine functionality is limited not only by the topography of the terrain, but also by the terrain constitution. Whereas hard rock poses no serious problem to legged robots, muddy terrain can hamper its operation to the point of jamming the machine. Still, under such adverse conditions, legged robots offer a better maneuverability than other vehicles (Angeles, 2007; Siegwart & Nourbakhsh, 2004). The main disadvantages of legged locomotion include power andmechanical complexity. The leg, which may include several degrees of freedom, must be capable of sustaining part of the robotSs total weight and, in many robots, must be capable of lifting and lowering the robot. Additionally, high maneuverability will only be achieved if the legs have a sufficient number of degrees of freedom to impart forces in a number of different directions. In the last few years, this feature has given rise to a number of research activities on the subject. Despite all these efforts, the performance of legged robots is still far from what could be expected from them. This is true particularly because the robots performance depends on several factors, including the mechanical design, which sometimesmay not be changed by the control designer (Estremera & Waldron, 2008). Legged robots present some problems that are not usual in wheeled robots. For example, problems such as trajectory planning and stability analysis need a good kinematics and dynamics model of the system. 12