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• Developing a novel 2-DOF spherical joint with a large continuously rotatable range. • Using a C-shaped rail mechanism to avoid collision and to enlarge workspace. • Developing a dynamic model of the joint for behavioral analysis. • Building a prototype of the joint, and experimentally confirming the functionality of the joint. The development of an innovative two-degrees-of-freedom (2-DOF) active spherical joint (universal joint) that can provide an extended range of motion and perform continuous rotation in both DOFs is reported. The workspace of the 2-DOF joint in general arrangements is explored. To overcome the structural limitation of the general configurations of the joint, this work proposes a new design that incorporates rotatable C-shaped rails to avoid collision among components of the joint. The dynamic model of the 2-DOF joint is constructed, and its behaviors in the simulation are analyzed. The trajectories are generated in simulation to better understand the joint torque requirement. A prototype of the 2-DOF joint was fabricated, and its performance was experimentally evaluated. The experimental results confirm that the continuous rotation of the two DOFs in a wide range is feasible and that the RMSEs of positions were less than 2% within the motion range, and those of orientations were less than 0.6% along the entire rotations, with standard deviations under 0.4 mm and 0.6 degree. [ABSTRACT FROM AUTHOR]

• Development of a spherical robot that can leap while rolls. • Using a five-bar linkage mechanism and a release/retract mechanism for leaping. • Using a differential drive to actuate two semi spheres for rolling and turning. • Dynamics of rolling and leaping are analyzed. • The robot can leap up to 1.14-times of radius to overcome a barrier while rolls. To improve robots' mobility on flat ground and rough terrain, we designed and implemented a novel spherical robot with a combined rolling and leaping capability. The robot has two individually driven semi-spheres, which generate rolling and turning motions. The robot also has a five-bar linkage with a release/retract mechanism for leaping. The release/retract mechanism only uses one DOF to control and switch the mechanism in three different stages: retracting, maintaining, and releasing. In this paper, the dynamics of the robot in rolling and leaping are analyzed. The robot was empirically built, and its performance was experimentally evaluated. The results confirm that the robot can leap close to 25.4 cm diameter of the sphere, which, to the best of our knowledge, is the best among reported spherical robots. The robot can also leap while rolling over a 14 cm barrier, which is equal to 1.14 times the sphere's radius. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: We designed and implemented a novel omnidirectional spherical robot. Instead of using wheels or flywheels, a driven ball is installed inside the spherical shell and driven by two orthogonally-mounted rollers; thus, the omnidirectional mobility of the robot with no singularity can be achieved by simple forward kinematic mapping. The dynamic model of the robot is derived, and effect of the model's parameters is evaluated in simulation and discussed. The simulation results also serve as the design guideline for building the empirical system. Several design issues are addressed to ensure the robot's proper development. Finally, the spherical robot is built, and its performance is quantitatively and experimentally evaluated, thus proving its omnidirectional and trajectory-controllable mobility. [Copyright &y& Elsevier]

• A novel module capable of fast transforming its shape between a wheel and a leg. • The maximum leg length approximately 3.4 times the wheel radius. • Can perform wheel-to-leap behavior. • Leaping height up to 4.6 times the wheel radius. We report on the development of a novel two-degrees-of-freedom module capable of transforming its shape between a wheel and a leg, with the length of the latter approximately 3.4 times the wheel radius. The leg-wheel module was empirically built and experimentally evaluated. It utilizes a linkage mechanism and can perform a smooth yet rapid leg-wheel transition within 0.25 s. The design concept, selection of the linkage parameters, and kinematics are described in this paper. The rapid transition from a wheel to a leg endows the robot with wheel-to-leap behavior. The general motion planning strategy of the leg-wheel, as well as the wheel-to-leap behavior, are explained in the demonstration example. The results confirm that the module can perform wheel-to-leap behavior with a height of up to 4.6 times the wheel radius. [ABSTRACT FROM AUTHOR]