A robot capable of locomotion in both air and water would enable novel missions in complex environments, such as water sampling after floods or underwater structural inspections. The design of such a vehicle is challenging, implying significant propulsive and structural trade-offs for operation in both fluids. This thesis examines the aerial-aquatic locomotion problem applied to miniature robots, beginning by exploring the ways in which this type of locomotion is achieved in nature, to abstract design principles for synthetic systems.
After examining the problem, several subsystems enabling aerial-aquatic locomotion are presented. This includes multiple devices for escape from water using a pressurised jet, with each device taking a different approach to overcoming the power density limitations of miniature actuators, including the use of compressed gas, combustion, and elastic energy storage. Each system is able to rapidly release stored energy as thrust, allowing a robot to transition to flight from water. Using the highest performing system, the aquatic escape process is examined, by tracking launches out of water in a laboratory. From this data a model is developed and the robustness of launch in an outdoor environment is quantified. For sustained locomotion, a means of optimising propeller performance in two different media simultaneously is examined, and a bimodal transmission which allows efficient operation both air and water is produced.
The tested subsystems are integrated into an Aquatic Micro Air Vehicle (AquaMAV) capable of sustained flight in air and dives into water. This robot uses a reconfigurable wing to dive into the water from flight, inspired by the plunge dive of Sulid birds. The vehicle’s performance is investigated in wind and water tunnels, and its behaviour is analysed using a trajectory model. The performance of the AquaMAV and its subsystems are then assessed, and the impact of the multimodal capabilities on performance is examined.