Design and motion analysis of a coal mine robot with variable wheel diameter

In response to the complex unstructured environment of coal mines, a design scheme for variable wheel diameter robots is proposed. Based on the gear, connecting rod and sliding rail mechanism, a wheel with variable diameter was designed. Through the change in the wheel diameter of the robot, the obstacle-crossing ability and terrain adaptation ability of the robot were improved. The kinematic model of a single wheel was established and the variation rule of radial length was analysed. The kinematics model of the whole vehicle was established, and the motion state of the robot under different driving speeds was analysed. Based on RecurDyn software, the robot turning, wheel diameter change process and obstacle surmounting process were simulated. Through 3D printing technology, the robot prototype was made, and the limit obstacle crossing test was carried out. Simulations and prototype tests show that the smallest radius of the wheel radius change is 107 mm, the largest radius is 158 mm, and the limit height for the robot to cross obstacles is 172 mm. After the wheels are unfolded, the centroid of the robot rises by 50 mm, and the fluctuation amplitude of the centroid of the robot when walking with the maximum radius is 3.6 mm. The diameter was increased by 47.6% through the gear, link and sliding rail mechanism, and the exceeding limit height was increased by 60.7% compared with the common wheel-type robot. Compared with tracked and legged robots, the robot designed in this article has high flexibility and lightweight. It can reduce the wheel diameter and accelerate forward on flat roads, and when encountering obstacles, it can increase the wheel diameter to improve obstacle crossing performance. This provides new ideas for the research of special detection robots and the intelligence of coal mines in the future.