Design and Implementation of a Novel Spherical Robot With Rolling and Leaping Capability

Spherical robots have been widely used in surveillance, planetary exploration, and child-development because of its capability of moving in all directions and its sealed environment to protect inner electronics. However, spherical robots still face difficulties when encountering high obstacles or rough terrains. Past research has not been able to resolve these difficulties well. In this research, our goal is to design and implement a spherical robot combining rolling and superior leaping motion. In addition, compared to general jumping robots, spherical robots has a better landing ability because of its spherical shape. The spatial limitation and the large overall weight are the two major challenges of designing jumping ability of spherical robots. To tackle these two challenges, we propose an innovative design of a spherical robot. The proposed spherical robot consists of two parts: the rolling part and the leaping part. The rolling motion is achieved by rotating each semi-sphere on a fixed axis. The differential speed between the two semi-spheres allows the robot to turn. For the leaping part, we implement a four-bar mechanism to store energy by spring and an energy storage mechanism to adjust the four-bar mechanism. The four-bar linkage has a non-linear force-displacement curve, which not only can store more energy under the specific limitation of motors but also can prevent premature lift-off while releasing energy. To maximize the storing energy under the maximum torque of the servo motor and the spatial limitation of the robot, we use force analysis to derive the relation between linkage lengths and the output leaping vertical force. The optimal length of the linkage lengths is obtained by exhaustively searching all various curves of different linkage lengths. Besides the four-bar linkage for the leaping part, the storing mechanism will wind up the strings, thus pulling up the four-bar mechanism to store energy. The energy storage mechanism combines all the functions of a ratchet, a pawl, a partial gear, and a one way bearing. Our design allows us to use one degree of freedom to control the storing and releasing process. The energy storing mechanism has two important characteristics: compact and modularized. First, through special design, we are able to arrange all the components in a compact space in the bottom part of the robot. Therefore, the structural rigidity can be strengthened to withstand the high torque of motors during the storing process. Second, the modularized characteristic improves assembling efficiency and allows us to adjust our design without affecting other parts of the spherical robot. To jump at a desired angle, we study the system dynamics to estimate the desire jumping angle. Our spherical robot can be simplified as a two-wheeled pendulum model. Lagrangian mechanics is used to derive the equation of motion of the system. The simulation results show a periodic phenomenon of the swing angle of the pendulum. Our final implementation of the spherical robot has a total weight of 2.9 kg and a diameter of 25.4 cm. The spherical robot can jump with as high as 26.5cm, with an average jumping height of 24.5 cm. The spherical robot can also successfully combine rolling and jumping motion to jump over 12 cm obstacles. In conclusion, this study successfully designs and implements a spherical robot with great leaping ability to improve its mobility. The rolling, leaping, and combination of rolling and leaping motion of the spherical robot is achieved. The experimental outcome indicates that the jumping ability is the best of existing spherical robots to the best of our knowledge. Keywords: Spherical robot, rolling robot, jumping robot, energy storage, four-bar linkage