Constructing rolling mechanisms based on tetrahedron units

In this paper, a tetrahedron unit constructed by connecting three links to a node via revolute joints is proposed. A closed loop mechanism is constructed by combining two tetrahedrons units to share a common face with three spherical joints such that the geometric structure of the mechanism is a triangular bipyramid. We show that the structure of the mechanism enables it possess a rolling function when proceeding on the ground. Furthermore, with the similar topology structure, two more closed-loop rolling mechanisms are obtained by combining 4 and 6 units, respectively. Due to the similar rolling principles of the proposed mechanisms, it suffices to analyze the rolling feasibility of the triangular bipyramid mechanism. By analyzing the kinematics, the deformation features of the mechanism are obtained. Upon some proper controls, we show that these features enable the mechanism to roll and switch directions when it proceeds on the ground. These functions are verified by a series of simulations with a 3D model and experiments with a prototype.