Cavity-Membrane-Based Water-Jet Bio-Inspired Thruster With Multidirectional Accelerating Capability

Water-jet propulsion helps aquatic creatures achieve both accelerated motion (e.g., flying squid) and long-endurance cruising motion (e.g., jellyfish). That inspired the development of the aquatic unmanned aerial vehicle (AquaUAV) and underwater soft robots. Underwater soft robots achieve water-jet propulsion in all directions but have little propulsion thrust, AquaUAV has large propulsion thrust but can only accelerate from underwater to air. Here, to improve their deficiencies, we proposed a novel water-jet thrusters using cavity-membrane-based water-jet (CM-jet) structure. To quantitatively test the propulsion performance of this novel structure, a tethered prototype as well as a force-pressure measurement system was built. Propulsion theoretical models were developed and refined to explain the propulsion process of CM-jet structure. To explore and verify the propulsion rules, the launch angles $\alpha$ (0$^\circ$, 15$^\circ$, 30$^\circ$, 45$^\circ$, and 60$^\circ$) and the initial pressure (0–0.3 MPa) of thruster were varied in the experiments. By combining simulation and experimental results, the thruster using CM-jet structure exhibited propulsion stability independent of launch angles. The maximum net peak thrust is 130 N when $\alpha$ = 30$^{\circ }$ and $P$ = 0.3 MPa. With stable propulsion at any directions, the CM-jet structure may broaden the accelerating directions of water-jet, realizing three translational DoF, which provides a faster propulsion pattern apart from propeller for underwater robot and AquaUAV.