Hindawi Journal of Robotics Volume 2021, Article ID 5542920, 26 pages https://doi.org/10.1155/2021/5542920 Review Article Review on Unmanned Underwater Robotics, Structure Designs, Materials, Sensors, Actuators, and Navigation Control Javier Neira, Cristhel Sequeiros, Richard Huamani, Elfer Machaca, Paola Fonseca, and Wilder Nina Veox Inc., Arequipa, Peru Correspondence should be addressed to Wilder Nina; [email protected] Received 21 February 2021; Accepted 7 June 2021; Published 6 July 2021 Academic Editor: L. Fortuna Copyright © 2021 Javier Neira et al. (is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Since its beginning, around the 50s decade, until present days, the area of unmanned underwater vehicles (UUV) has considerably grown through time; those have been used for many tasks and applications, from bomb searching and recovery to sea exploration. Initially, these robots were used mainly for military and scientific purposes. However, nowadays, they are very much extended into civils, and it is not hard to find them being used for recreation. In this context, the present research is an effort to make a walkthrough of evolution in this area, showing a diversity of structure designs, used materials, sensor and instrumentation technologies, kinds and the number of actuators employed, navigation control techniques, and what is new in development trends. (e paper gives a clear starting point for those who are initializing into this research area; also, it brings some helpful knowledge for those who already have experience. 1. Introduction to have an impact on the future survival of humanity. (at is why researchers have strived to develop unmanned vehicles Robotics is a branch of engineering that involves the con- that are increasingly efficient and can provide work and cept, design, manufacture, and operation of programmable maintenance services underwater, as well as explorations of machines, which can develop their autonomy in the exe- ever deeper marine environments. For example, there are an cution of a specific task. Submarine robotics can be sub- estimated 2 billion tons of manganese nodules in the Pacific divided as shown in Figure 1, where one can identify those Ocean near the Hawaiian Islands [2]. related to underwater robotics (unmanned water vehicles). (e UUVs are identified in Figure 1. Mainly, they are Underwater robotics have been developed for decades, and subdivided into those that are remotely operated (ROV) and they were characterized by manned water vehicles devel- those that are autonomous (AUV). (e ROV is a vehicle opment. However, in the last decades, due to the cost joined to an umbilical cable, and, according to its applica- demanded by the construction and use of these vehicles, tion, it can be classified into observation, work, and special researchers led to the development of robots or unmanned purpose [3, 4]. ROVs play a vital role in military operations underwater vehicles (UUV), where each time the robots (e.g., torpedo and mine recovery), rescue operations (e.g., were optimized and used in a wide variety of applications for locating historic shipwrecks, such as the RMS Titanic), and the benefit and sustainable development of the planet. Since critical oil and gas operations. In recent years, the range of there is an immense magnitude of the oceans and due to the vehicles and mimitizing the need for human operators have human difficulty for their exploration, the vast majority of increased due to research efforts. However, we have au- them have not yet been explored (two-thirds of the planet) tonomous vehicles (AUVs); these are indispensable tools, and around 37% of the world’s population is less than mainly for ocean exploration tasks. (ey are built using 100 kilometres from the ocean [1]. (is means that various high-end technologies and equipped with several of knowledge of the marine environment has and will continue them [5, 6]. During the subsea exploration process, the AUV 2 Journal of Robotics Robots Unmanned Workers Zoomorphic Humanoids vehicles Industrial With wings Androids Space Of service With legs Aerial With fins Terrestrial Aquatic Figure 1: Location of unmanned water vehicles within a basic robotics classification. performs necessary maintenance and repairs, transports the movements, such as jellyfishes, stingrays, and sharks. Even necessary equipment, and monitors and records different though underwater robots that use thrusters with symmetrical situations under exploration. In oceanographic research, the geometric shapes are generally more efficient, many works in AUV may be used in various measurements; one of them is bioinspired robots are being developed and continue looking to for the observation, release, and recovery of instruments increase knowledge in this study area. related to the monitoring of submarine volcanoes, in ad- dition to carrying out surveys of the seabed and various studies in areas such as biology and hydrology. 2.2. By Hull Type. Some robots work underwater; those are (e unmanned vehicles’ structural designs have been of two hull types, open and close. (e open ones generally based on their shape, actuators’ distribution, and materials have a hermetic box that is over a frame, and the other used. (ey include monitoring and measurement tasks of components like engines, buoyancy elements, sensors, and oceanographic variables and navigation of the UUV; to lights are over it too, while the closest ones have a bigger case achieve these objectives, it will be necessary to have a di- that covers all elements; they do not have a frame because all versity of sensors. Everything presented is the subject of elements are inside of the case. (e prototypes or designs analysis in this article. (is article is structured as follows: which have a close hull usually have a cylindrical or round Section 2analyzes the morphologies used which are char- geometric shapes; for example, there are some which look acterized by their type of hull and geometric shape and those like a torpedo or a sphere. that are bioinspired; additionally, it considers the distri- bution of propellants, materials used, and hermeticity. 2.3. By Geometric Shape. One of the most famous shapes of Section 3presents the instrumentation and actuation ele- underwater robots is the cylindrical shape, and on the top ments used interchangeably in ROVs and AUVs. Section they have the appearance of a dome, which means they look 4analyzes the navigation, orientation, and movement’s like a torpedo. In 1973, one of the first portable ROVs was control of both ROVs and AUVs. Finally, the conclusions of made, and it had a torpedo shape as shown in Figure 2. this work are presented in Section 5. (e robot was hydraulically controlled from the surface, and it began to be controlled with electricity. (at was the main 2. Structural Designs and Used Materials reason of its popularity, ten years later, 500 prototypes were sold. (ose kinds of shapes come from military technology 2.1. Morphologies. (e morphological review refers to un- developments like many other technological advances. In this derwater robots’ geometrical shape, which is dependent on specific situation, the form comes from torpedoes that were on many factors like internal electronic devices distribution, military ships; this is the case of MK-38. sensor, motors, structure stability, and drag coefficient de- In the Applied Physics Laboratory of Washington fined to move the robot, among others. Additionally, it must University, some modifications to a torpedo were made, and take the robot’s degrees of freedom into account, since this is it became an inspiration to create the REMUS robot in 1994 needed to locate motors in the structure correctly. [8]; a schematic of such robot is shown in Figure 3. (is kind of robot does not necessarily have a geometrical (e design was of a cylindrical shape, and it moved shape; there are many ROVs and AUVs with biomimetic thanks to only one propeller behind the robot and four fins structure; (at is to say, they try to mimic aquatic animal’s behind the propellers; two of them were located on a vertical Journal of Robotics 3 (ere are new studies that have been done during the last few years about different shapes of underwater robots. In comparison, those have advantages compared with tradi- tional shapes, since their forms are symmetrical. In an in- vestigation project, the goal was to control the position of the symmetrical robot in events of disturbances with a pro- portional change of the direction force from propellers; all their motors were inside of the closed hull. (e design was developed in 2012, and it had a diameter of 40 cm and weighted 6.3 kg. (is spherical robot is shown in Figure 8. (e assembly of the mechanical components which are Figure 2: Snoopy ROV [7]. inside of the robot was made manually, and it caused troubles in the robot’s operation underwater because the robot was less stable, and it could not move for long periods. axis, and they had their drive mechanism like the ones that Figure 9 shows some of the improvements made with a 3D were located on a horizontal axis. (ey were there to give printer to fabricate the mechanism for the water jets [15]. direction to the robot. (e robot had a length of 114 cm with (e robot has two servomotors and a water jet in each leg. a diameter of 18 cm and a weight of 40 kg. (e torpedo shape For its movements, one servomotor is first turned vertically is still used because of hydrodynamic advantages. to lift the propeller of the water jet; then, the horizontal In 1997, the REMUS robot’s development continued with servomotor moves the propeller of the water jet to go for- one smaller model that a person could uphold and transport.