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About this book

This book reports on the state of the art in the field of aerial-aquatic locomotion, focusing on the main challenges concerning the translation of this important ability from nature to synthetic systems, and describing innovative engineering solutions that have been applied in practice by the authors at the Aerial Robotics Lab of Imperial College London. After a general introduction to aerial-aquatic locomotion in nature, and a summary of the most important engineering achievements, the book introduces readers to important physical and mathematical aspects of the multimodal locomotion problem. Besides the basic physics involved in aerial-aquatic locomotion, the role of different phenomena happening in fluids, or those due to structural mechanics effects or to power provision, are presented in depth, across a large dimension range, from millimeters to hundreds of meters. In turn, a practice-oriented discussion on the obstacles and opportunities of miniaturization, for both robots and animals is carried out. This is followed by applied engineering considerations, which describe relevant hardware considerations involved in propulsion, control, communication and fabrication. Different case studies are analyzed in detail, reporting on the latest research carried out by the authors, and covering topics such as propulsive aquatic escape, the challenging mechanics of water impact, and a hybrid sailing and flying aircraft. Offering extensive and timely information on the design, construction and operation of small-scale robots, and on multimodal locomotion, this book provides researchers, students and professionals with a comprehensive and timely reference guide to the topic of aerial-aquatic locomotion, and the relevant bioinspired approaches. It is also expected to inspire future research and foster a stronger multidisciplinary discussion in the field.

Table of Contents

Frontmatter

Breaking the Surface

Frontmatter

Chapter 1. Breaking the Surface

Abstract
Most animals use different forms of locomotion to move through a varied environment. This allows them to adapt to find food, escape threats or migrate, while minimising their energetic cost of locomotion. To do so, animals must use the same locomotor modules to perform specialised tasks that often have opposed requirements. For example, an animal diving into the water to hunt requires a structure that is as lightweight as possible for efficient flight, whilst still being structurally strong when impacting the water’s surface.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 2. Why Swim and Fly?

Abstract
We live on a water-covered planet that is facing rapid change, both globally and locally, due to a combination of human behaviour and natural phenomena [31]. Understanding these changes requires in-depth scientific understanding of our environment. Key to enabling this is the fast, accurate and repeated provision of extensive physical data. However, obtaining dependable geospatial data is itself frequently a challenge, requiring new sensing approaches or considerable adjustments to existing methods.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 3. Aerial-Aquatic Locomotion in Nature

Abstract
Water covers 363 million square km, or 72% of the earth’s surface. The vast majority of this water is saline (96%), frozen (2%) or groundwater (1%). The 10\(^5\) km\(^3\) of surface freshwater (0.008%) is in turn concentrated almost entirely in three large great lake systems (Fig. 3.1), with a vanishing small amount of surface freshwater forming lakes and rivers.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 4. Synthetic Aerial Aquatic Locomotion

Abstract
A wealth of research exists into the broader question of how robotic mobility can be expanded beyond a single domain/terrain. A significant amount of recent research attention has been given to the implementation of aerial-terrestrial mobility into miniature robots [94], resulting in mobile robots with shared subsystems and additional mechanisms which are analogous to the AquaMAV robot presented in Chap. 7.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 5. The Physics of Aerial Aquatic Locomotion

Abstract
This chapter presents an overview of some fundamental physical laws and concepts at play in generic, as clarified in Figs. 5.1 and 5.2. The vehicle-specific physics are then introduced in the following chapters and form the basis for locomotion derived for the different vehicles presented.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Practical Aerial Aquatic Locomotion

Frontmatter

Chapter 6. Aquatic Escape: Fast Escape with a Jet Thruster

Abstract
In a previous chapter an idealised water jet thruster was analysed, and it was argued that the most effective system would use large pressures to drive a small volume of water. In this chapter a more detailed physical model of water jet propulsion will be introduced, and the key design features of a jet thruster prototype detailed. Consistent static thrust from the fabricated device is then demonstrated.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 7. Airframe Design for Plunge Diving

Abstract
In this chapter the design of a plunge diving AquaMAV is detailed. This enhanced AquaMAV prototype is capable of propelled flight, wing retraction for diving into water and jet propelled aquatic escape. The selection process for key components is detailed, as well as the specific attributes necessary for aerial-aquatic locomotion. The AquaMAV includes some limited automation, to allow the robot to self launch when in water, where radio communication is challenging.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 8. Diving from Flight

Abstract
Having measured the longitudinal aerodynamics of the AquaMAV in wind tunnel tests (cf. Chap. 7), the data gathered can then be used to analyse the dive performance of the vehicle, as well as estimate and evaluate its dynamic properties. As in Sect. 6.​4, we begin by considering a quasi-steady state model, where, furthermore, the aerial and aquatic phases are considered separately and transition phases are omitted. This model is used to obtain planar dive trajectories for both the purely aerial and the purely aquatic phase, providing a clear overview of the achievable performance of the robot. In the second part of the chapter, a more detailed model of the vehicle is developed that accounts for some dynamic effects and explicitly includes the air-to-water transition. The latter model is used to obtain more insight into the vehicle dynamics and into the impact phase. It also serves as a basis for simulations covering several envisaged mission stages.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 9. Aquatic Escape: Repeatable Escape with Combustion

Abstract
Several systems have been developed with aerial-aquatic locomotion capabilities but without demonstrating consecutive transitions to flight from water. Moreover, while some multirotor vehicles possess the ability to operate in both air and water [108, 109], the transition to flight is typically constrained to very calm sea conditions. Fixed-wing robots able to transition dynamically between water and air through high-power thrust bursts represent a low-cost, versatile and more reliable solution. Compared to multirotor vehicles, this approach that would simultaneously result in an increased flight range and allow for aquatic escape in a wider variety of conditions.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 10. Efficient Water-Air Propulsion with a Single Propeller

Abstract
In the previous chapters, aquatic launch and dives into water with small flying robots have been demonstrated. An AquaMAV prototype was presented which was capable of self propelled-flight in air and able to escape water, but this robot had no means of propelling itself beneath the surface. To add aquatic locomotion it is attractive to use the same propulsion system as is used for flight, as this reduces the weight and complexity of the system. However, the increase in load on the propeller in a denser fluid results in much slower rotation speeds, and means a significant loss of motor efficiency.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 11. Sailing and Flying with a Multimodal Robot

Abstract
The field of aerial-aquatic robotics promises tremendous benefits in data collection as well as unmatched flexibility and remote access. However, the majority of existing aerial-aquatic robots are unable to perform scientific tasks at significant depth, limited by the weight penalty that any pressure resistant container would add. In addition, sealing of an actuated robot is difficult, again adding significant weight to small systems. Wireless communication is a major challenge for underwater robots and certainly poses great constraints to operation at distance. Lastly, underwater propulsion is often highly inefficient due to geometries optimised for flight [109]. Indeed, most aerial-aquatic vehicles either have severely limited water range and operation, stay in very shallow waters or function only in de-ionised water. Too often, the benefit of underwater locomotion is overshadowed by the weight, and complexity increases that are required for reliable operation. This negatively impacts flight performance.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 12. Multirotor Aircraft and the Aquatic Environment

Abstract
The previous chapters presented hybrid robot concepts and prototypes relying on the use of fixed wings for lift generation. The higher flight efficiency of such devices makes them suitable for covering large distances and can even serve to extend their locomotion envelope (see Chap. 11).
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 13. Practical Tips for Building Aerial-Aquatic Robots

Abstract
This book would not be complete without a chapter on practical hardware and software elements used throughout the presented robots. We hope that this can serve as a rough toolbox for aerial-aquatic vehicle development, and cover some of the prototyping choices that are often under-reported in academic literature, but consume outsize research time.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Chapter 14. Conclusion

Abstract
This book introduces the concept of small, unmanned aerial-aquatic robotics. This novel field of research aims to merge the benefits of flight and aquatic operation into one lightweight autonomous platform. As the reader will have seen in this book, wildly different robots can be envisioned as solutions to this formidable challenge.
Raphael Zufferey, Robert Siddall, Sophie F. Armanini, Mirko Kovac

Backmatter

Additional information