High-Power Propulsion Strategies for Aquatic Take-off in Robotics

The ability to move between air and water with miniature robots would allow distributed water sampling and monitoring of a variety of unstructured marine environments, such as coral reefs and coastal areas. To enable such applications, we are developing a new class of aerial-aquatic robots, called Aquatic Micro Aerial Vehicles (AquaMAVs), capable of diving into the water and returning to flight. One of the main challenges in the development of an AquaMAV is the provision of sufficient power density for take-off from the water. In this paper, we present a novel system for powerful, repeatable aquatic escape using acetylene explosions in a 34 g water jet thruster, which expels water collected from its environment as propellant. We overcome the miniaturisation problems of combustible fuel control and storage by generating acetylene gas from solid calcium carbide, which is reacted with enviromental water. The produced gas is then combusted in air in a valveless combustion chamber to produce over 20 N of thrust, sufficient to propel small robots into the air from water. The system for producing combustible gases from solid fuels is a very compact means of gas storage, and can be applied to other forms of pneumatic actuation and inflatable structure deployment.