Flexible gait transition for six wheel-legged robot with unstructured terrains

The flexibility of gait and trajectory planning with heavy payload are the main challenges for legged stable walking of hexapod robots in unstructured terrain, especially in time-varying and local terrain mutation conditions. To guarantee adaptability in unstructured terrain environment, the factors, including the obstacle height, terrain depth, and secure foothold as well as stability state, should be considered in the gait and trajectory planning. In this article, a novel gait transition hierarchical control framework based on a flexible gait planner (FGP), and gait feedback regulator (GFR) with behavior rules is proposed for the developed hexapod wheel-legged robot (BIT-6NAZA). The core of this gait planner is to select the optimal footholds and change gait types according to secure foothold and stability margin and kinematic margin of legs, and the GFR is applied to modify the foot-end trajectory of the selected gait according to the terrain feedback information to adapt to unstructured terrain. Finally, taking BIT-6NAZA robot as an example, the simulation and experiment are carried out under the proposed control framework. The co-simulation and experimental results show that the robot can modify the foot-end trajectory in dynamic unstructured terrain and obtain elastic gait in obstacle avoidance.