Analysis of climbing in circular and rectangular pipes with a reconfigurable sprawling robot

This paper presents an analytical description and experimental results for a reconfigurable field robot that can climb inside circular and rectangular pipes. The robot is fitted with two mechanisms that allow it to change its width and height and shift its center of mass (COM) to adapt itself to the size of the pipe. We start by describing the kinematic model of the robot as a function of its sprawl and four bar extension mechanism (FBEM). Next, we develop a force analysis based on the robot's geometry, its configuration, the position of its center of mass (COM), the diameter of the pipe, and the coefficient of friction (COF). We then develop strategies for driving, climbing and transitioning between the two modes. Although a high COF increases the robot's grip, it reduces its ability to reconfigure its shape, which it needs to transition between its climbing/driving modes. Based on this analysis, we designed a control algorithm comprised of actuation sequences to automatically drive the robot inside pipes, including the transition phases. The results show that the robot successfully executed its climbing tasks (see video).