Brainstorming: Platform Design

The stability and functionality of a Rov depends on the platform upon which it is built. A common idea is to build a frame out of PVC tubing which all components can be mounted too. Since water flows through the rov there is little resistance but very high speeds are impossible to obtain due to the friction causing body shape. A hydrodynamic body may be formed using sheeting or fiberglass. This will increase the overall speed of the Rov and make it more stable in the water, although it can also lessen the amount of room left to mount equipment. On Appendix II, which is shown below, I have sketched multiple designs which will be considered.

Design number one uses a long and skinny body to help increase the speed of the Rov. This design uses three motors to propel it through the water. The two forward motors swivel up and down to change the rov's depth in the water. The rear motor turns left and right to steer the Rov. This rov is very good at moving quickly since it may turn at full power. When operating at slow speeds the Rov may become difficult to handle and keep in one place. An arm can easily be mounted to the front of the platform although care must be taken to evenly balance the Rov.

In figure two a round design is considered. This rov will resemble a saucer and is capable of making precise movements at slow speeds. This Rov also employs three motors to work. Two are mounted on the left and right side which propel the Rov forward and turn it. A third is mounted vertically and is used to change the Rov’s depth. This design uses a closed body and is capable of moving quickly. Care must be taken when changing depth as the rotary movement of the vertical motor may cause the Rov to spin. If this becomes apparent it can be fixed by adjusting the trim on one of the motors to produce slight propulsion which will cancel out the movement from the vertical motor.

Figure three is designed as an all purpose Rov frame and makes use of less motors. Only two are used and they are mounted horizontally on the roof of the Rov. This makes sure that they will not be blocked by any of the other components. One problem that could arise is if the motors float above the water and are unable to propel the Rov. This is why a variable ballast tank is used instead of a third motor. The box in the middle will contain a variable ballast tank. When empty the Rov will have negative buoyancy and sink below the surface. When inflated the Rov will have positive buoyancy and float to the surface. If inflated fully the Rov will rise out of the water which can be helpful in retrieving items from the bottom of the test tank. Like all the designs an arm may be mounted although care must be taken to not throw off the balance of the Rov.

The fourth and final design is a larger Rov. It is meant to be very thin and should not weigh too much. Two motors are used on the left and right wings of the Rov. These can be operated independently to steer the rov left and right. A large paddle is built near the tail which can be adjusted to change the dive plane of the Rov. To change depth the Rov will also employ a variable ballast tank which will give it stability when operating in a stationary spot. This Rov will have less propulsive force due to the need to shut a motor off to turn, but will make up for it with its aerodynamic shape. The hull will be constructed of a fiberglass and a large hole will be left in the front to accommodate any type of robotic arm. This hole can also be used as a storage compartment if the tasks require one.While all these designs are possible and have been used to compete in the past the ultimate decision will come from the team and their decision on the attributes required of the Rov. It is important to keep in mind the electronic usage of motors and how this can be avoided by using pneumatic and hydraulic power. The size of the Rov must also be carefully decided as the larger and heavier it is the slower it will move due to the restricted amount of energy.

Brainstorming: Robotic Arm

The robotic arm is a crucial item in the Rov construction. Many of the tasks rely solely on its effective use. Having an easy to use multipurpose arm may be the key to winning the MATES competition. I have sketched out various designs as seen in Appendix I, which is at the end of this post.

The first design uses a hydraulic system. The arm is locked down in two pivot points indicated by the circle with a cross in the middle. It is then connected to a hydraulic arm that may either extend or retract. In this design creating a negative pressure and retracting the hydraulic arm closes the space between the two gripping arms. This design is simple and is useful for grabbing delicate items. It would best be used when an item must be retrieved and returned to the surface. The fact that it closes relying on a negative pressure means it is easy to keep the arm closed, however large amounts of force may not be applied as this could cause leaks that would let water into the closed system.

The second design relies on an electronic motor. This design has one stationary arm, which is shown on the left side of the drawing, and one arm connected to a geared motor. The gear allows a greater torque to be applied to the arm. This design requires greater monitoring from the control station. If care is not used the motor may easily become overworked and burn out, rendering the arm useless. This arm is best suited situations where large amounts of force are needed for short amounts of time, such as grabbing and pulling an item.

The third design also relies on a hydraulic arm, which is useful as it does not require excess energy. The arms are locked into pivot points in the middle of the arms as shown by the circles with a cross in them. This design, unlike the first one, requires a positive pressure from the control station to close the arm. This makes it easier to apply more force, although care must be taken not to create a tear or leak within the line. This is useful for grabbing items with large amounts of force and holding them for an extended period as the hydraulic line may simply be locked at the required pressure. This differs from the second design in that although they both can produce greater force, there is no risk of burning out the motor from extended use. A pressure gauge would be very useful in this design as it will make it easier to produce the required force and lower the risk of exceeding the maximum pressure of the system.

The fourth design is similar to the second in that one arm remains completely stationary. The second arm is attached by mobile rods that allow it to extend and retract. This design is shown running off a hydraulic system although it could easily be adapted to use a motor or servo. This design is also locked down in multiple locations to provide a secure base. This design is useful as it is less prone to breaking off from the main body. Its narrow profile is also useful for a situation where there is little room to maneuver the arm, such as reaching inside a hole. This same profile limits the design as it is unable to grasp large items.

While all these designs will prove effective if constructed properly, the true deciding factor will depend upon the tasks assigned. The construction of multiple arms may even be necessary to accommodate varying tasks. The use of hydraulics instead of electronics allows more energy to be focused on the motors, increasing their speed.

Abstract Works Cited

MATES Rov Competitions. MATE Center. Copyright 2007. 8/13/07.
http://www.marinetech.org/rov_competition/index.php

Abstract

In the spring of 2008 a competition will take place where multiple teams will compete using the remotely operated vehicles they have designed. The winners will then go on to compete with other teams around the world. The Rov’s must be designed following the specifications and limitations set forth by the MATES competition and are constructed by the students that make up the team. The team must also be prepared to give a presentation on the design process involved in building their Rov.

The purpose of the Marine Advanced Technology Education Center competition is to prepare the future workforce for marine-related careers (MATE). This is done by organizing student groups from middle schools through high schools who work together to design and construct a Rov. The Rov must be constructed as a multi-purpose platform which can be modified to fit the tasks of the competition, which are released about three months before the first competition. Below in Figure 1 a team is seen controlling their Rov by watching the cameras onboard.

Figure 1
Teams compete by a poolside control station (MATES).

Throughout the entire process the organizers of the competition have very strict safety guidelines. These are used to protect the students from industrial hazards that they may not have been thoroughly warned about, and to emphasize the danger that comes from working in a marine environment. One of the greatest dangers is electrocution through an improperly sealed connection. This is why a thorough safety check is performed before the Rov’s are allowed to enter the water. The constant emphasis on these safety checks teaches the competitors to do a complete job on every aspect of the project. As shown in Figure 2 below, the likelihood of a mistake becomes greater with the complexity of the Rov. Unlike in a land environment, a simple mistake in a marine environment can lead to the loss of an entire vehicle.

Figure 2
Teams must check all parts of the ROV before competition to avoid costly mistakes (MATES).

While the competition tasks change from year to year they are always focused on the global issues of the time. A major theme has been global warming and the use of Rov’s to study its effect. While it is impossible to predict what this years tasks will be, it can be assumed that a mobile platform capable of holding a robotic arm will be needed. The platform must also be able to raise weights from the bottom of a test tank, whether it is through the use of variable buoyancy or motorized propulsion. The Rov must also be able to withstand the depths of a standard pool. It is very important that the Rov be capable of moving swiftly through the water as all tasks are judged by time. The Rov must also be tethered and controlled by a station set up next to the waters edge. In Figure 3 below teams are seen preparing to compete from the side of the pool. Onboard cameras must also be employed as it is the only visual connection the pilot will have with the Rov.

Figure 3
Students preparing to compete (MATES).

While designing and constructing the Rov many factors must be considered. These include the material selection and size of the Rov. One that is too large will move slowly through the water and be difficult to transport. One made of weak materials may break before ever reaching the competition. The Rov must be small enough that it can be lifted and placed into the water without any mechanical help such as a winch. A good size to aim for would be one that could be carried by a single person.

Before the teams even begin to compete they must present their project to the sponsors and managers of the competition. The teams tackle this problem in varying ways from prepared speeches to the use of poster boards and PowerPoint presentations. Whatever a team’s technique may be it is important that they do the best job they can as a large portion of their score comes directly from this presentation. Below a team is seen presenting their Rov in figure 4.

Figure 4
Teams must present their design to an audience before competing (MATES).

While winning this competition is the ultimate goal, the skills learned during the process of designing a Rov are skills that will stay with you your whole life. It may even be enough to spark an interest in a lifelong passion. The Mates competition is solely based to inform students of marine related careers and it is experiences like these that will help you decide what career to pursue.

Background Information Works Cited

Underwater Archaeology. Copyright 2006-2007. 9/18/07.
http://www.underwaterarchaeology.com/tools-of-the-trade.htm.


NOAA Ocean Explorer. 9/17/07.
http://oceanexplorer.noaa.gov/technology/subs/hercules/welcome.html.


Artic logistics information and support. 9/18/07.
http://siempre.arcus.org/4DACTION/wi_alias_fsDrawPage/1/132.


The Deep. Copyright 2007. 9/18/07. http://www.lophelia.org/thedeep/basics2.htm.

Research Works Cited

“Dynamic Buoyancy Control of a Rov using a Variable Ballast Tank”.
K. S. Wasserman. 8/15/07. http://web.mit.edu/miwolf/www/rovpaper.pdf.


“Foam and fiberglass ama construction”. Gary dierking. 8/20/07.
http://homepages.paradise.net.nz/garyd/quikama.htm.

MATES Rov Competitions. MATE Center. Copyright 2007. 8/13/07.
http://www.marinetech.org/rov_competition/index.php.


“PVC Fittings”. 8/27/07. http://www.pacificpondsplus.com/pvc_fittings.htm.


“PVC Helpful Hints”. Omni Industries Limited. 9/1/07.
http://www.omniindustriesltd.com/main_helpful.htm/.

“Robotic Arm Control”. 7/27/07. http://www.jhu.edu/~virtlab/robot1/robot.htm.


“Rov buoyancy”. 8/19/07. http://www.rov.net/pages/rbouyan.htm.


RoveXchange. “What is a Rov?”. 8/12/07.
http://www.rovexchange.com/mc_rov_overview.php.

“Rov Propulsion”. Work Ocean. Copyright 1995. 8/12/07.
http://www.jhu.edu/~virtlab/robot1/robot.htm.

“The Robotic Arm”. Tom Harris. 7/30/07. http://science.howstuffworks.com/robot2.htm.


“What is a Rov?”. 8/12/07. http://www.rov.org/educational/pages/whatis.html.

Research

What is a Rov?

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).

Expectations

After construction of the robotic arm is completed it is expected that it will function correctly. It is important that the arm be able to clamp onto both a small item, and a larger heavy item. The arm must be tested in the pool to judge the arms performance while submerged. To test this multiple items will be placed on the bottom of the pool. These items will mimic those of the competition as much as possible. The entire rov will then be assembled and used. This not only tests to see that the robotic arm functions correctly but that the entire Rov functions as well. This is a time where many adjustments can be made. The robotic arm will also be expected to have at least two degrees of motion. This will allow the arm to be maneuvered into place. This will be tested first out of water to ensure that a reasonable range of motion is achieved, as well as in water to be sure that the arm functions the same and all components are waterproofed correctly. The arm must also be strong enough to hold at least ten pounds of weight, while the more the better. This however will not be tested until the point of destruction as it will not be possible to build an entirely new arm in time.

Testing Procedures

To test the robotic arm three separate tests must be performed. The first step involves testing the range of motion in a dry environment. This involves connecting the robotic arm to the Rov and setting up the control station. All ranges of motion will be tested to their extremes multiple times. Upon completion of this test a similar one will be performed in the water. The Rov will be submerged in the test tank and all components will be tested. The third test involves construction of items that resemble those of the competition. It is impossible to predict what exactly these items will be, but it can be assumed that the arm must be capable of moving a small and delicate item, as well as a larger heavy item. Through careful examination of the rules released in January the items will be designed and constructed. After the construction of these items they will be gently placed on the bottom of the test tank as not to cause damage. The entire Rov will then be placed in the water and a slow run will be performed to become accustomed to all controls of the Rov. Once all tasks are completed they will be re-set in the bottom of the pool. Now the Rov will be tested operating at its maximum speed. This will be timed and the data will be used to predict the Rov’s performance in the competition. The pool used in the competition can be seen in Figure 1 below.

Figure 1
MATES competition test tank (MATES).

1. Assemble Rov arm onto Rov.
2. Connect all control wires through tether to the control box.
3. Using the control box operate the robotic arm through all ranges of motion out of water.
4. Submerge Rov in test tank.
5. Using the control box operate the robotic arm through all ranges of motion in water.
6. Place previously constructed items resembling those of the competition on the bottom of the test tank.
7. Slowly complete all tasks to be sure they are possible using the current set up.
8. Reset items on the bottom of the test tank.
9. Complete all tasks as fast as possible while using a timer.

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