Development of a Deep Sea ROV
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Published: Thu, 05 Apr 2018
- Jeremy Moros
Australia’s geographical location places it within reach of 65% of the world’s salt water oceans. However, to this day, only 0.9% of the oceans depths have been explored. This journal explores whether or not current technologies allow for the possibility of a series of imagery and sensory underwater drones gathering data from unexplored biological habitats and ecosystems, where the costs and safety of human expeditions have been prohibitive. To discover these depths the proposal for an Unmanned Scientific Data Gathering and Collection System (USDGCS) has been explored to determine whether existing open source platforms such asArduino can be utilised to create a system where once deployed can collect and redistribute first hand data live across the internet. The drone must be designed to perform a large array of tasks, whether it be the photographing and mapping at extreme depths, or the monitoring species populations close to the surface. Ultimately, a model that is friendly to the environment in which the ROV operates is essential so the self-powering drones have been explored.
Underwater Drone, Ocean, Remotely Operated Vehicles, UAV
ROV’s are commonly referred to as an acronym for “Remotely operated vehicles”. ROV’s can be classified as one of two types of drones, Underwater ROVs and aerial UAVs (Unmanned Aerial Vehicles). Similar principles allow for the similar technologies in such drones however the medium in which they operate differ. In each classification, drones such as AUVs (Autonomous underwater vehicles) do not require constant control from a human, but instead rely on prewritten algorithms. These algorithms make use of self-navigating equipment such as using sensors and radars to determine their location and perform functions with an accuracy dependent on the equipment on board.
The extreme water pressure experienced at depths below a few hundred meters are enough to kill a human. ROV’s were developed to overcome the limitations of deep-sea divers where they have proven to be of much use in the gas and oil industries. The first form of a drone was the 1960’s HOV or Human Operated Vehicle. However basic, it demonstrated the very first development of drone technologies. It was the US Navy that funded and developed more of early ROV technologies through the 1960’s program “Cable-Controlled Underwater Recovery Vehicle” (CURV). This vehicle was created to be cable of performing sophisticated deep-sea rescue operations, such a recovering black boxes from previously destroyed military aircraft and retrieving highly dangerous devices such as a nuclear weapons. The “CURV” removed any danger to the humans that operated them and was considered as a milestone in technology. However, many of the technologies incorporated into were developed for scientific research purposes. ROV’s today underwent development when drones were developed for scientific research purposes. These technologies include the addition of live streaming video cameras and lights sources, where it became easier for a ROV to be precisely controlled by an operator. Now in the 21st century, many components are commonly integrated to expand a vehicle’s capabilities. These may include mapping sonars, magnetometers and high resolution digital cameras, as well as more sophisticated tools such as instruments that can accurately determine water temperature, clarity and light penetration. Specialised drones may feature cutting arms or manipulators that can gather rock or flora samples for low depth environments (<100meters)
- Purpose of investigation
The purpose of this investigation is to determine whether current technologies allow for the successful development of a deep sea ROV where data can be collected and redistributed live through the World Wide Web without costs being prohibitive.
2 Context: Parts of a ROV
The ROV is commonly consists of 4 systems, each of which serve a specific function.
2.1.1 The Frame: The frame of a ROV serves as the primary skeleton of the vehicle. Often constructed beams, struts or plates as the frame bears the load of the water pressure. The frame often defines the overall shape of the ROV as mechanical and electrical components often need to be secured inside the frame for successful operation. This includes weights, pressure canisters, thrusters, floats, camera, lighting and other instruments like manipulator arm, sonar, scientific sensors, etc. ROV frames can be made from a range of materials including plastic composites and aluminum tubing and the choice is based on the developmental requirements of a ROV. Due to the highly saturated salt solution in the ocean, corrosion resistant materials with high strength and low density have been favorably considered. Since weight has to offset with buoyancy, this is critical. A well designed frame aims for easy repair if components are to fail, as well as a shape that will aid easy control.
2.1.2 Buoyancy System: A ROV owes its ability to stay afloat due to its buoyancy system. The principle to the floatation of an ROV is the attainment of neutral buoyancy of the ROV system as a whole. If neutral buoyancy is achieved, a ROV is capable of floating in water and can rise and descend when needed. There are many ways in which buoyancy can be achieved, the most simple being the attaching of floats to a ROV. In more sophisticated ROVs, a dedicated buoyancy system is incorporated into the design. A Ballast system is of two types, an active and static ballast system. An active Ballast system is more sophisticated as it can adapt to changes in weight of a system. A static ballast system is far less sophistical, where floats and other simply floating devise such as air filled cans provide a fixed buoyancy range beyond which the ROV will sink to the ocean floor. However, if the static ballast system has a fixed buoyancy too great, the ROV will never dive, no matter the thrust from a propulsion system.
2.1.3 Propulsion System: Thrust is required for the control of a ROV, which is provided by a propulsion system. The thrust produced should be more than the drag force acting on the system, thus a more aerodynamic design is advised. A range of propulsion systems have been developed, however the most common would be a combination of bilge pumps and underwater rotors to propel the craft. The motor inside a ROV should be adequate to propel the ROV forward, as well as stop it in a short time. High torque motors of 800-2000 RPM rotors are considered to be sufficient for underwater drones. The number of thrusters required is dependent on the functions a ROV will perform. It is known that the greater the number of thrusters, the more freedom in the movement of the ROV. The propeller attached can be a 3 blade or 5 blade depending on the speed and water density through which the ROV will traverse. Brushless DC motors are preferred over other types of motors due to the fact that they offer a higher efficiency, hence offering better control of a ROV’s speed. DC motors are often far cheaper than a similarly outputting AC motor.
2.1.4 The Electronic System The electronic system of the ROV encompasses the payload of the ROV. The ROV system should have a water tight enclosure for the electronic and electrical components. A variety of electrical components are used for a number of purpose such as driving power, lighting and video feed, etc. The wiring should be secure and watertight to ensure that the chances of water damage to electronics is kept to a minimal chance. The wiring is often kept far clear of the rotors to reduce any chance of entanglement. The video feed can either be stored on an on-board system or transferred to the control room via a tether or a however recent technological advancements are allowing for a wireless connection to the surface. The ROV often receives electrical commands through the same radio device as the video feed, whether it be wired or wireless. Micro Controllers are considered an ideal option for analogue control as development is not required for a new embedded PC board, hence lowering costs. The Arduino platform utilizes these micro controller boards and is an example of a cheap, but effective solution. These controllers allow for sensory data to be collected from various instruments. Some ROVs are designed to incorporate instruments where they are capable of performing a standard set of operations. The power source of a ROV is dependent on the depth it is required to travel. Low depth ROV’s are able to leave a power source on the surface and are powered by an electrical cable. However, a ROV designed to dive deep proves a long electrical cable impractical and therefore warrant onboard batteries with 5-12 Volts. A photovoltaic cell can be installed on the ROV and be used to recharge the battery when resurfacing.
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