Underwater minirobots actuated by hybrid driving method

Underwater minirobots have attracted significant interest due to their value in complex application scenarios. Typical underwater minirobots are driven mainly by a soft or rigid actuator. However, soft actuation is currently facing challenges, including inadequate motional control accuracy and the lack of a continuous and steady driving force, while conventional rigid actuation has limited actuation efficiency, environmental adaptability, and motional flexibility, which severely limits the accomplishment of complicated underwater tasks. In this study, we developed underwater minirobots actuated by a hybrid driving method (HDM) that combines combustion-based actuators and propeller thrusters to achieve accurate, fast, and flexible underwater locomotion performance. Underwater experiments were conducted to investigate the kinematic performance of the minirobots with respect to the motion modes of rising, drifting, and hovering. Numerical models were used to investigate the kinematic characteristics of the minirobots, and theoretical models developed to unveil the mechanical principle that governs the driving process. Satisfactory agreement was obtained from comarisons of the experimental, numerical, and theoretical results. Finally, the HDM was compared with selected hybrid driving technologies in terms of acceleration and response time. The comparison showed that the minirobots based on HDM were generally superior in transient actuation ability and reliability.