Analysis on nonlinear turning motion of multi-spherical soft robots

A modular multi-spherical soft robot, which consists of five deformable spherical cells, two friction feet, the electromagnetic valves and the control systems, is constructed. According to the deflating action and the inflating action of the spherical cells, the size and the shape of each spherical cell can be changed. With two friction feet sticking with the ground in turn, the soft robot can move forwards, make a turning motion and avoid the obstacle. This paper creates a nonlinear relation between the pressure P and the inflation radius \(\left( r \right) \) at different original radii \(\left( {r_0 } \right) \) and obtains the inflation or deflation velocity \(v_r \). Six inflating and deflating steps to finish the turning motion are presented. Based on the geometric relationship between the inflation radius (r) and the original radius \((r_0 )\) of each cell, the nonlinear turning process is described to control the center positions (x, y, z) of the spherical cell. Last, a simulation and an experiment of five spherical cells are shown to emulate the turning process. Experiment results show that the robot has a maximum turning capability of \(20{^{\circ }}\) in one period.