Lightweight robots are capable of repeated aquatic jump-gliding through high-powered jet propulsion with water-reactive fuel.

Despite significant research progress on small-scale aerial-aquatic robots, most existing prototypes are still constrained by short operation times and limited performance in different fluids. The main challenge is to design a vehicle that satisfies the partially conflicting design requirements for aerial and aquatic operation. In this paper we present a new class of aerial-aquatic robot, the Sailing Micro Air Vehicle, ‘SailMAV’. Thanks to a three-part folding wing design, the SailMAV is capable of both flying and sailing. The robot design permits long and targeted missions at the water interface by leveraging the wind as movement vector. It simultaneously offers the flexibility of flight for rapidly reaching a designated area, overcoming obstacles and moving from one body of water to another, which can be very useful for water sampling in areas with many obstacles. With a total wingspan of 0.96 m, SailMAV employs the same wing and actuation surfaces for sailing as for flying. It is capable of water surface locomotion as well as take-off and flight at a cruising speed of 10.8 m/s. The main contributions of this paper are (i) new solutions to the challenges of combined aerial and aquatic locomotion, (ii) the design of a novel hybrid concept, (iii) the development of the control laws required, and (iv) the demonstration of the vehicle successfully sailing and taking off from water. The presented work can inform the design of hybrid vehicles that adapt their morphology to move effectively.

Unmanned aerial vehicles (UAVs) have been shown to be useful for the installation of wireless sensor networks (WSNs). More notably, the accurate placement of sensor nodes using UAVs, opens opportunities for many industrial and scientific uses, in particular, in hazardous environments or inaccessible location. This publication proposes and demonstrates a new aerial sensor placement method based on impulsive launching. Since direct physical interaction is not required, sensor deployment can be achieved in cluttered environments where the target location cannot be safely approached by the UAV, such as under the forest canopy. The proposed method is based on mechanical energy storage and an ultralight shape memory alloy (SMA) trigger. The developed aerial system weighs a total of 650 grams and can execute up to 17 deployments on a single battery change. The system deploys sensors of 30 grams up to 4 meters from a target with an accuracy of ~10 cm. The aerial deployment method is validated through more than 80 successful deployments in indoor and outdoor environments. The proposed approach has the potential to be integrated in field operations for data acquisition and can complement other robotic or manual sensor placement procedures. This would bring benefits for demanding industrial applications, scientific field work, smart cities and hazardous environments.

Flapping-wing MAVs are starting to emulate the advanced flight maneuverability of insects and birds, however they struggle to achieve a similar aptitude for taking off and landing in challenging cluttered environments. The ability to perch on objects such as branches or metal struts would result in a wide range of potential landing sites, both indoors and outdoors, and would increase the achievable mission duration, thus allowing a more versatile usage of MAVs. While perching is particularly challenging with flapping-wing MAVs, these vehicles are highly promising for complex missions in confined spaces. In this paper a systematic bioinspiration approach was adopted to design a new lightweight perching solution suitable for bird-size flapping-wing MAVs. The proposed concept combines a four-bar linkage mechanism with an active-passive actuation method to achieve a large gripping power at low energy consumption. Additionally it relies on compliant soft grippers inspired by the Fin Ray${}^{\circledR}$ effect, which lead to a high adaptability to different perching surface textures and shapes. A prototype of the proposed concept was manufactured and tested experimentally in gripping tests and rail-guided perching tests. With a total mass of 45 g the concept is suited for bird-size MAVs in the weight range of 150-300 g. Flight tests on a surrogate (multirotor) platform demonstrate the approach functions successfully in realistic free-flight conditions.

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].

Flapping-wing aerodynamic models that are accurate, computationally efficient and physically meaningful, are challenging to obtain. Such models are essential to design flapping-wing micro air vehicles and to develop advanced controllers enhancing the autonomy of such vehicles. In this work, a phenomenological model is developed for the time-resolved aerodynamic forces on clap-and-fling ornithopters. The model is based on quasi-steady theory and accounts for inertial, circulatory, added mass and viscous forces. It extends existing quasi-steady approaches by: including a fling circulation factor to account for unsteady wing-wing interaction, considering real platform-specific wing kinematics and different flight regimes. The model parameters are estimated from wind tunnel measurements conducted on a real test platform. Comparison to wind tunnel data shows that the model predicts the lift forces on the test platform accurately, and accounts for wing-wing interaction effectively. Additionally, validation tests with real free-flight data show that lift forces can be predicted with considerable accuracy in different flight regimes. The complete parameter-varying model represents a wide range of flight conditions, is computationally simple, physically meaningful and requires few measurements. It is therefore potentially useful for both control design and preliminary conceptual studies for developing new platforms.