Reconfigurable robots consist of many modules which are able to change the way they are connected. As a result, these robots have the capability of adopting different configurations to match various tasks and suit complex environments. For mobile robots, the reconfiguration is a very powerful ability in some tasks which are difficult for a fixed-shape robot and during which robots have to confront unstructured environments (Granosik et al. 2005; Castano et al. 2000), e.g. navigation in rugged terrain. The basic requirement for this kind of robotic system is the extraordinary motion capabilities. In recent years considerable progress has been made in the field of reconfigurable modular robotic systems, which usually comprise three or more rigid segments that are connected by special joints (Rus, D. and Vona, M. 2000). One group of the reconfigurable robots featuring in interconnected joint modules realizes the locomotion by virtue of the structure transform performed by the cooperative movements and docking/undocking actions of the modules (Suzuki et al. 2007; Kamimura et al. 2005; Shen et al. 2002; Suzuki et al. 2006; Vassilvitskii et al. 2002). Because the modules in these robots are not able to move independently and the possible structures of the robot are limited, these kinds of robots are not suitable for the field tasks. The other kind of reconfigurable robots being composed of independently movable modules is more suitable for the field environment. The first prototype (Hirose et al. 1990) with powered wheels was designed by Hirose and Morishima in 1990, which consists several vertical cylindrical segments. The robot looks like a train, however with a weight over 300 kg it is too heavy. Klaassen developed a mobile robot with six active segments and a head for the inspection of sewage pipes (Klaassen et al. 1999). There are twelve wheels on each module to provide the driving force. Mark Yim proposed another reconfigurable robot PolyBot which is able to optimize the way its parts are connected to fit the specific task (Yim et al. 2000). PolyBot adopts its shape to become a rolling type for passing over flat terrain, an earthworm type to move in a narrow space and a spider type to stride over uncertain hilly terrain. The application of powered tracks to field robots enriches their configurations and improves the adaptability to the environments. A serpentine robot from Takayama and Hirose