Design and analysis of a spherical wheel-legged hybrid robot with leg adjustment modules for enhanced locomotion performance

The motion performance of spherical wheel-legged hybrid robots in quadruped mode is constrained by their spherical shell structure, resulting in limited strides. This paper proposes a novel spherical wheel-legged hybrid robot equipped with leg adjustment modules, drawing inspiration from the motion mechanism of spinal joints in reptiles. These modules facilitate the movement of the leg modules through gear mechanisms, enabling them to function as eccentric pendulums in spherical mode and to replicate the function of spinal joints in quadruped mode. A kinematic analysis of the leg mechanism was conducted using the vector method. Further analyses addressed the linear and turning motion characteristics of the quadruped mode, influenced by the leg adjustment module, leading to the planning of the corresponding gait. Simulations were performed in Adams, along with a series of analyses, to validate the accuracy of the theoretical model. A prototype was developed and tested for its mode conversion, linear motion, and turning performance. The experimental results demonstrate that the robot can smoothly switch between spherical and quadruped modes. In quadruped mode, its turning radius decreased significantly. With a spherical diameter of 300 mm, the stride length increases from 158mm to 201mm, and the linear speed rises by 27.2% as the initial adjustment angles increase from 0° to 19°. These improvements collectively enhance the locomotion performance of the robot, as intended.