Energy-Based Control of a Thruster-Assisted Underwater Hexapod Robot on Deformable Terrains

The thruster-assisted underwater hexapod robot can traverse structures with any dip angle, such as a drilling platform and hip hull. However, the structures are often deformable due to complex coverings, which significantly complicates the leg–terrain interaction dynamics and poses a substantial hurdle in steering the robot. Thus, we propose and experimentally implement an energy-based control method for a thruster-assisted underwater hexapod robot with C-shaped legs. The key idea is to calculate the robot's energy loss during locomotion and use thruster forces to compensate for it. First, we establish leg–terrain interaction mechanics by considering the leg's special shape and the terrain's viscoplastic characteristics. Then, we use it to calculate the robot's required energy for tracking the predesigned locomotion. Second, we introduce an energy-based control method that effectively coordinates thruster forces and torques, where the torques are designed to guide the legs in tracking the predesigned gaits, and the thruster forces are calibrated based on the remaining energy. Finally, as demonstrated in our contrastive lakebed locomotion experiment, this approach enables the robot to navigate deformable terrains smoothly.