Mode-characteristic planning for land-air amphibious vehicles on unstructured terrain

Land-air amphibious vehicles are extensively used in various environments owing to their high mobility and endurance. Nevertheless, it is considerably challenging to ensure their safe and reliable operation in unstructured environments, such as uneven terrain and multi-domain dynamic properties. Existing studies assume the flat-ground condition and consistent constraints in air and ground modes, which significantly limit the mobility of the vehicle. Therefore, a mode-characteristic planning method is proposed for integrating a terrain assessment module in the ground mode and relaxing dynamic constraints in the air mode. The planner first employs an accelerated kinodynamic RRT* strategy to generate an initial hybrid trajectory. Compared to graph-search methods, the sampling method employed in this study achieves a more reasonable mode-switching mechanism. Furthermore, valid travel planes are constructed using terrain-assessment results in the ground mode. Ultimately, parameterized trajectory optimization and differentiated dynamic boundaries are applied to refine the three-dimensional trajectory, which is subsequently transmitted to the amphibious controller for flexible flying or high-maneuver driving. Extensive experiments are conducted in both simulated and real-world environments to demonstrate the efficiency of the system. Compared with the search-based method, the results show that mode-characteristic planning increases the ratio of the ground trajectory in the hybrid trajectory by 15.74 % and reduces motion time by 9.20 %, thereby improving multi-domain mobility.