Aerial-aquatic robots possess the unique ability of operating in both air and water. However, this capability comes with tremendous challenges, such as communication incompatibility, increased airborne mass, potentially inefficient operation in each of the environments and manufacturing difficulties. Such robots, therefore, typically have small payloads and a limited operational envelope, often making their field usage impractical. We propose a novel robotic water sampling approach that combines the robust technologies of multirotors and underwater micro-vehicles into a single integrated tool usable for field operations. The proposed solution encompasses a multirotor capable of landing and floating on the water, and a tethered mobile underwater pod that can be deployed to depths of several meters. The pod is controlled remotely in three dimensions and transmits video feed and sensor data via the floating multirotor back to the user. The 'dual-robot' approach considerably simplifies robotic underwater monitoring, while also taking advantage of the fact that multirotors can travel long distances, fly over obstacles, carry payloads and manoeuvre through difficult terrain, while submersible robots are ideal for underwater sampling or manipulation. The presented system can perform challenging tasks which would otherwise require boats or submarines. The ability to collect aquatic images, samples and metrics will be invaluable for ecology and aquatic research, supporting our understanding of local climate in difficult-to-access environments [Video attachment: https://youtu.be/v4xWmEHUSM4].
The hybrid aerial underwater vehicle (HAUV) merges the best of unmanned aerial vehicle (UAV) and unmanned underwater vehicle into one platform makes it possible to operate in both the air and water. Various possible applications of HAUV have aroused much research on it. However, the underwater endurance and operation depth of current HAUVs are still limited. This hinders the application and popularization of HAUV in rugged environments. This paper presented the design, fabrication, and testing of a novel concept HAUV, Nezha III. It is featured by its piston-driven underwater glide strategy and combination of an underwater glider and fixed-wing vertical takeoff and landing aircraft. In-depth design and evaluation of the amphibious wings with tradeoffs between aerodynamic and hydrodynamic performance in both fluids was conducted. The vehicle prototype was built, and field experiments, including domain transitions and underwater operations, were conducted in Qiandao Lake, China. Due to the experiment site constraints, the computational fluid dynamics technique evaluated horizontal flight performance with fixed wings. The experimental results show that the prototype can realize rotor flight and stable domain transitions. Moreover, this piston-driven underwater glide strategy extended the HAUV's underwater endurance over 24 h and operational depth to 25.5 m. To the best of our knowledge, Nezha III possesses the most extended underwater endurance among existing HAUVs.
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