A remotely operated vehicle is a robot that can be controlled from a safe location, while venturing into hazardous areas (ROV). Rov's were originally designed by the military but later became commercially successful as the need for offshore drilling platforms rose (ROV X). A Rov is not restricted to water as they are also used on land for studies on volcanoes and radiation areas. An underwater Rov is usually a small device that is connected by a tether to the control station, usually on a ship. Through this tether all data gathered by the Rov is sent back to the ship. It is also used as a means to recover the Rov in the case that something goes wrong (ROV). There are two general types of Rov’s. The first is a “work class” Rov that is used for deep water trenching and construction. This type is often controlled by a large crew and the Rov can be very large itself. The second type is an observation Rov . This is usually a smaller vehicle that can move quickly and is used to observe and study the marine environment (ROV X). It is also important that a Rov uses a tether that is neutrally buoyant to allow it to float easier through the water (ROV). A Rov is seen observing marine life in figure 5 below.
Figure 5
Rov observing marine life (Rov X).
Underwater Propulsion
There are three main systems used to propel a Rov. These are electric, hydraulic, and ducted jet propulsion. One of the main goals in choosing the correct propulsion system is to expand the operating window of the Rov. If a powerful system is chosen and the Rov can work in rougher currents than it can also make more frequent trips and increase the yearly revenue of the crew. It has always been important to regularly maintain equipment to avoid a catastrophic failure. This is why most major components are replaced very 50 to 100 operating hours. It is important to choose a system only meant to perform a few different types of tasks. If too many tasks are sought than the Rov will require more equipment and grow exponentially to fit it all (Rov Propulsion).
PVC Construction
When working with PVC it is important to make sure a clean cut is made. An uneven cut reduces the surface area of the bonding agent and can lead to leaks. PVC should only be installed when the temperature is between 40 and 110 degrees Fahrenheit. If the temperature is too extreme the cement will not dry properly. It is also important to check to make sure all the pieces fit together correctly before applying cement. When cementing PVC pipe to a fitting a thick layer of cement should be applied to the pipe equaling the length that should fit into the adapter. A medium layer should be applied inside the adapter. Then both pieces must be connected without delay. After cementing both pieces together they should be held together for a short period of time to avoid a separation of the pieces. A small cloth should then be used to wipe away the bead of cement that forms at the joint (PVC Fittings). All pieces of PVC should be deburred and cleaned before cementing together. While cutting it is also important to use a miter box (PVC Helpful Hints).
Fiberglass Construction
Fiberglass can be very useful in building a body to your Rov. While it is not necessary it can do wonders in increasing the hydrodynamics of your vehicle and make it move quickly through the water. A fiberglass shell is also capable of holding all materials in place and providing stability to a Rov. The easiest method to use is the foam and fiberglass construction. This involves making a mold out of foam blocks which the fiberglass can be constructed on top of. The foam used must be closed cell foam, which often costs more. To know if the foam is closed cell look for the little beads inside it. If you see any this means it is not closed cell and it should not be used (Foam and Fiberglass). The foam can easily be shaped with electric sanders for major changes and normal sandpaper for minor adjustments. A piece of fiberglass being shaped is shown in figure 6 below.
Figure 6
Foam mold being made (Foam and Fiberglass).
Robotic Arms
An underwater robotic arm must be designed very carefully to avoid damage during use. The arm should be constructed of the strongest materials possible and made as simple as possible to avoid errors. Modern robotic arms can be very expensive and sacrifices must be made to fit a small budget. The use of pivot points, levers, and gearing can help to make a very powerful and reliable arm with a minimum use of power and materials. A robotic arm can either be controlled imprecisely through switches, or very precisely through the use of a computer program (Robotic Arm control). The most common robotic arm used in construction is a large arm with seven metal segments connected by six joints. At each joint a motor is placed. These joints allow the arm to move in any direction and perform any nearby task. This type of arm requires large amounts of materials and electricity and would be too large for a Rov (The Robotic Arm). When less amount of movement is needed smaller robotic arms can be made. Some may be as simple as having one degree of movement like a claw opening and closing. Others may be able to spin, move inwards and outwards, up or down, or in any direction required(The robotic Arm). A very complex robotic arm is seen below in Figure 7.
Figure 7
A complex robotic arm building a car (The Robotic Arm)
Underwater Buoyancy control
When constructing the Rov it is important to decide whether to have a variable buoyancy control so that you may raise and lower your Rov’s level in the water with ease, or if a neutral buoyancy should be seeked so that the Rov’s depth may be changed with the use of directional motors. A variable ballast system would employ the use of an onboard tank that may be filled with air or water. Depending on the level of air in the tank determines the Rov’s buoyancy. There are two ways to operate this onboard tank. An air supply may be left on the surface and connected through the Rov’s tether. This system reduces the onboard bulk of the system and allows the ballast level to be changed by simply opening a valve or using a bike pump. A complete onboard system may be used where a compressed air tank is stored on board. If set up correctly this system is much more reliable as there is less chance of leaking. Care must be taken however to not overuse the tank as it will run out of air (Dynamic buoyancy). Neutral buoyancy may also be seeked as it will improve the operators control over the Rov. The closer a Rov weighs to the amount of water it displaces, the less work the motors must do to propel the Rov. This is important in reaching faster speeds and getting the most out of a limited power supply. The Rov’s buoyancy also controls how much of a payload it can carry (Rov buoyancy).
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