Analysis of the constraint relation between ground and self-adaptive mobile mechanism of a transformable wheel-track robot

To maneuver in unstructured terrains where the ground might be soft, hard, flat or rough, a transformable wheel-track robot (NEZA-I) with a self-adaptive mobile mechanism is proposed and developed. The robot consists of a control system unit, two symmetric transformable wheel-track (TWT) units, and a rear-wheel unit. The TWT unit is the main mobile mechanism for the NEZA-I robot, with the rear-wheel unit acting as an assistant mechanism. Driven only by one servomotor, each TWT unit can efficiently select between track mode and wheel mode for optimal locomotion, autonomously switching locomotion mode and track configuration with changes in the terrain. In this paper, the mechanism structure, the self-adaptive drive system, the locomotion mode and posture of the NEZA-I robot are presented, the kinematic relation of the inside parts of the TWT unit is analysed, and the mathematic model of the constraint relation between the mobile mechanism and the ground, abbreviated to "MGCR model" is set up for the NEZA-I robot to go through some typical unstructured environments. The mechanism parameters, which influence the self-adaptability of the NEZA-I robot, are found and optimized. Basic experiments show that the mobile mechanism has the self-adaptability to navigate in unstructured terrains and has superior obstacle-negotiating performance, and that the MGCR model and the analysis method of mechanism parameters are reasonable. From a mechanism point of view, it can provide an idea for research on the adaptive control of the robot.