The ubiquitous Single Board Computer, the Raspberry Pi, or the RBPi is a perfectly suitable candidate for CORATAM or Control of Aquatic Drones for Maritime Tasks. Sitting within each drone, an RBPi becomes a part of a swarm of robotic systems. Portugal is using this novel method for exploring and exploiting its maritime opportunities as the sea is one of the country’s main resources. Although land-based and air-based swarms of robots have been extensively used for studying the aquatic environment for the proposed expansion of Portugal’s continental shelf, swarms in aquatic environments are a different breed altogether.
Tasks in aquatic environment are usually expensive to conduct. This is because of all the special operational requirements of manned vehicles and support crews. Therefore, Portugal has thought of an alternative approach where they have used collectives of relatively simple and inexpensive aquatic robot swarms. As each robot is easily replaceable, these have a high potential of applicability for essential tasks such as prospecting sites for sea border patrolling, bridges inspection, sea life localization, environmental monitoring, aquaculture, and so on.
The collectives of robots work on a decentralized control based on the principles of self-organization. This gives them the capability of performing efficiently on tasks that require robustness to faults, scalability, and distributed sensing.
With the development of CORATAM, Portugal is hoping to achieve three main objectives. The first is to explore the novel approach of control synthesis in a set of maritime tasks, but in the real world. The second is to develop a swarm of aquatic robots with fault-tolerant ad-hoc network architecture, heterogeneous in nature and scalable. The third is to disclose all the hardware and software components developed under an open-source license, to enable others to build their own aquatic robots.
Each robot is about 60 cm in length, and inexpensive, as the designers have used all widely available, off-the-shelf hardware. Each robot uses a differential drive mono-hull boat, which can travel at a maximum speed of 1.7 m/s, in a straight line. The maximum angular speed the robots can achieve is 90°/s.
An RBPi-2 SBC supports the on-board control of each robot. They communicate via a wireless protocol (802.11g Wi-Fi) and each broadcasts its UDP datagram. The neighboring robots and the monitoring station receive the broadcast, forming a distributed network without any central coordination or a single point of failure. All robots are equipped with compass sensors and GPS, and each broadcasts its position to the neighboring robots every second.
All robots use prototype hardware, making it inexpensive when compared to the majority of the commercially available unmanned surface vehicles. Therefore, the robots serve as a platform suitable for research and development, and easily maintainable. Additionally, the open source nature of the platforms makes them suitable for different manufacturing processes, sensory payloads, design choices, and different actuators to be used.
An artificial neural network-based controller controls each robot. The normalized readings of the sensors form the inputs of the neural network, while the output of the network controls the actuators on the robots. Each sensor reading and actuation value is updated every 100 ms.