Ever wondered how a remotely operated device is designed? Well, building an underwater vehicle from scratch that doesn’t even need this degree of human intervention could be even more exciting. Let us see how Team Amogh has accomplished this and more.
Center for Innovation, IIT Madras calls itself a place where a student can ‘walk in with an idea, and walk out with a product’. Known within the institute as a place where students slog from midnight until daybreak, it encourages students to pursue innovative ideas and supports committed and ambitious student teams to participate in prestigious international competitions.
Team Amogh is one such team that has made IIT Madras’ first Autonomous Underwater Vehicle (AUV). This vehicle, codenamed AUV Amogh, is capable of performing a set of predefined tasks on its own without human intervention.
But why work on an AUV when there are many other interesting avenues needing attention? Ocean bodies cover over 70 per cent of the earth’s surface, but they remain unexplored to a large extent. Although industries making Remotely Operated Vehicles (ROVs) have taken up many underwater missions, there is still a need to develop AUVs, especially because there are places deep below in water where effective communication is an issue. Also, the research and development pertaining to underwater projects is progressing at a much slower pace as compared to land-based and air-based projects. Determined to push the envelope of underwater technology for exploration, the team decided to develop a fully autonomous underwater vehicle.
In their endeavour, the team has also proved their mettle in several competitions. They had their first taste of success in 2014 when they participated in the national competition — Student Autonomous Underwater Vehicle (SAVe) — organized by the National Institute of Ocean Technology. Outperforming all the other teams in every aspect, the team secured the first position. This success spurred them to participate in an international competition called RoboSub, conducted by the Association for Unmanned Vehicle Systems International (AUVSI). Competing against several teams, they emerged as strong contenders on an international level. Apart from these two competitions, they also participated in various innovation challenges and the vehicle has also been selected as one of the top student innovations across the nation.
As it turns out, like most other success stories, Amogh too had humble beginnings. The team had initially set out to build nothing more than an ROV which was stable and maneuverable. In this phase, they designed the frame and the hulls, decided on the material to be used, analyzed the structure, and came up with a waterproofing mechanism. While passing their prototype through a series of tests and upgrades, they faced numerous challenges, the biggest one being trying to make the vehicle waterproof. After a detailed examination of various options, they chose water-tight PVC pipes. These pipes were fixed tightly to both fore and aft ends of the hull, and then sealed using an epoxy substance.
Improving their prototype at every stage, they eventually built a self-powered ROV. The vehicle had lithium polymer (LiPo) batteries on board to power the thrusters. These batteries were controlled using a terminal connected to a wireless router, which was in turn connected to the vehicle through an ethernet cable.
The team’s success in the ROV phase further fuelled their ambition to build an AUV. However, this was by no means a mere continuation of their task until then. Each aspect of the AUV design demanded expertise in a specific area. Three sub-teams were formed to tackle this — the mechanical, the electrical and the software teams. Although these teams were carved out of the original team, they needed to function in coordination with each other.
Designing the AUV
Needless to say, the mechanical team was entrusted with the indispensable task of designing and manufacturing the vehicle. More precisely, they had to design the following parts: pressure hulls, frame, and camera enclosure.
Since pressure hulls provide a watertight enclosure for the vehicle’s electronics, their design could not be overlooked. A configuration of two cylindrical hulls was chosen because it helped reduce the resistance of the vehicle and provided enough room for the electronics to be mounted on. The bottom hull was chosen to be heavy in order to counter the buoyant forces that would push the vehicle out of water.
In order to achieve a higher speed per unit of power input, the hull was fitted with a nose having an ellipsoidal shape as it offered the least drag on the structure. Furthermore, simulations helped determine the thickness that would enable the hull to withstand the pressure of water at a depth of 10 metres. Being the backbone of any underwater vehicle, waterproofing was done meticulously. A customized cap, with grooves to accommodate two rubber o-rings, was permanently attached to the aft end of the top hull. The cap was further covered with a flat disc, which consisted of 8 co-axial holes (not visible in the figure) to mechanically squeeze the o-rings and ensure watertightness. In order to prevent any chance of water entering the hull, the gap between the cap and the flat disc was sealed using silicon grease.
The hulls and the peripherals were mounted on the supporting frame. The team developed three versions of the frame and estimated the resistance for these versions at different velocities. The minimum-resistance version that they ultimately selected had a remarkably low power requirement as well.
At this juncture, it is worth noting that an AUV is also required to perform certain slick maneuvering tasks. For this purpose, the vehicle was equipped with 6 thrusters to achieve control in 4 degrees of freedom. Two thrusters placed on either side of the frame facilitate surge (forward/backward motion) and yaw (tilting in its own plane) control. Two thrusters — fore and aft — positioned axially upwards provide heave control.
Powering the Motion
Let us now move on to the team without which the vehicle would be rendered powerless – the electrical team. They were responsible for power management, circuit design, and mission control. The electrical module consists of a Central Processing Unit (CPU), a micro-controller, power supply units, sensors, thrusters, and other essential peripherals.
The motherboard or the CPU, just as the one in your desktop, does the main job of image processing and mission controlling, and provides a platform for all the components of the vehicle to communicate with each other. The micro-controller controls the motion of the vehicle by changing the rotation speed of the thrusters, on receiving commands from the CPU.
The primary control board, an interface for various sensors used in the vehicle, initially had all the components soldered onto it by fitting the wire leads of the components into the holes on the board — referred to as through-hole technology in electrical hardware parlance. They re-designed the circuit using Surface Mount Technology (SMT), in which the components are mounted directly onto the control board. They were indigenously designed, except the surface of the board. This significantly reduced the size of the board because by having smaller or no leads, SMT components were smaller than their through-hole counterparts.
The bridge between the micro-controller and the thruster is the motor driver. It’s a circuit that draws power from the batteries, and drives the motor at the speed demanded by the micro-controller. By now, it is natural for the reader to assume that all such high-tech components, such as the micro-controller or the motor driver, were purchased from electronics stores in the market. However, that is not true. One of the seemingly insurmountable goals the teams set for themselves was to eschew ready-made components and design their own components instead. They intended to pursue this slowly, replacing the ready-made circuits with the ones they designed. This helped them build components tailored to their needs.
Among the most essential of these components were the thrusters which consumed about 80 per cent of the total power. As a result, they demanded high capacity batteries to run the vehicle. Therefore, four lithium polymer batteries which together lasted for a minimum of 45 minutes were chosen for the entire vehicle. The 2 higher voltage batteries powered the thrusters, and the remaining 2 low voltage ones supported all the other peripherals.
However, this isn’t all that there is to an AUV even when looking at it solely from an electrical engineering viewpoint. For anything to be autonomous, sensors are essential. Amogh uses 5 sensors — pressure sensor, inertial measurement unit (IMU), current sensor, voltage sensor and leak detection sensor — and a pair of cameras. The pressure sensor is used to determine the depth of the vehicle below sea level. The IMU measures the orientation of the vehicle in degrees. Current sensors were used to measure the current flowing through each device since a high surge in current might permanently damage the device. Since an excessive discharge of lithium polymer batteries leads to catastrophic failures, voltage sensors were incorporated to regularly monitor the voltage across the batteries. In order to prevent any damage due to water leaking into the hull, a circuit was built to identify the intrusion of water. Two circular probes were mounted near the end cap of the hull. Since water conducts electricity even with slight impurity, the voltage across these probes gets amplified in its presence. This voltage signal is sent to the microcontroller to trigger a shutdown of the system.
Steering the Ship
Last but far from least, the software team was responsible for image processing, mission controlling, and designing a simulator. The significance of their role can be best explained using the following example of a competition they participated in.
As per the problem statement in the RoboSub competition, the vehicle was supposed to touch 3 buoys. The vehicle was guided towards the buoy by a plank placed on the floor of the water body. The buoy had to be traced by the front camera before the AUV reached the end of the plank. Once the vehicle tapped the buoy, it would bounce back and traverse towards the other buoy, as before.
In order to achieve this, the vehicle leveraged 2 cameras, placed in the front and the bottom of the vehicle.
However, there was a challenge: the images weren’t clear enough for a spotted object to be detected. They had to be corrected to remove the blue tinge, a characteristic of underwater images, and brightened in order to improve visibility. Any image had to be preprocessed to ensure high chances of the corresponding object getting traced on the camera. How did they accomplish this?
Note that a camera treats images as being composed of a large number of tiny coloured squares called pixels. Each pixel is a combination of three colors — red, green and blue. So if a bluish tinge has to be made negligible, the red and green channels can be boosted in intensity.
In another such issue, water, because of its high refractive index, deviates light from its original path, leading to reduced visibility. The resulting dark images are corrected by a method called gamma correction. In this method, the RGB color space is converted to another color space called HSV (Hue, Saturation, Value). The dullness of the images can be rectified by increasing the saturation of the image. This leads to bright objects becoming brighter and the dark ones becoming darker.
Once the above preprocessing tasks were done, the image was examined to locate the objects. The front camera had to trace a buoy, while the bottom camera kept track of the plank to provide course correction. The objects are identified in 2 stages — the first is based on their color, and the second on their expected shape. The fraction of the area of the frame occupied by the object was determined. This would indicate how far the vehicle was from the object. In the case of the bottom camera, the distance of the vehicle from the bottom was ascertained from the plank dimensions. This would be used to control the height of the vehicle since the buoys were known to be located at a particular height.
Furthermore, the orientation of the plank with respect to the frame was determined to correct the path of the vehicle. As the vehicle got closer to the buoy, the area occupied by the buoy in the image got larger. Once it reached a certain threshold, the vehicle was programmed to move further, hit the buoy and come back to take another course.
The mission-controlling part of the software determined the power needed to be given to each of the thrusters to move along a particular course. Because the LiPo batteries had limited endurance and needed a significant amount of time to get charged, the team also designed a simulator to solve the challenges of mission controlling.
AUVs have a plethora of applications. They are used mainly in detecting leaks in oil pipelines deep in the ocean. They are even used in detecting corrosion in a ship’s hull, ballast tanks, piles of a dock, and oil tanks. A technique called non-destructive analysis, where theories pertaining to ultrasonic sound are used, can detect the thickness of the corrosive layer. These frequencies, in the order of a few MHz, penetrate the corroded layer before being reflected by the underlying metal.
Team Amogh’s project is representative of how student teams work together in groups to participate in competitions, taking charge of different lines of work to perfect every single component involved in the design of the vehicle. The team now plans to upgrade its present design by using brushless thrusters, and slowly transform it into a modular design. To be at par with the present day technology, they have also decided to use acoustic sensors to determine the vehicle’s location precisely. A startup, named Planys Technologies, has also emerged out of the project. Currently incubated in IIT Madras, Planys plans to deliver customized autonomous vehicles specific to different underwater applications.
Rahul Vadaga is a 4th year Dual Degree student in the Department of Electrical Engineering at IIT Madras. Fascinated by the idea of building things on your own, he joined the Center for Innovation (CFI). After a year-long thrilling ride at CFI, he decided to write about one of its notable and successful endeavours. He feels grateful to Immerse and Team Amogh for presenting him with an opportunity to do so. Of late, he has been exploring the area of Artificial Intelligence in order to understand its immense possibilities for the future. For comments or criticism, he can be reached at firstname.lastname@example.org
All images are courtesy of Team Amogh, CFI, IIT Madras.
Featured Image Credits: CC-BY-SA Erik Scott