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This material is based upon work supported by the National Science Foundation under Grant Numbers DRL/ITEST 1312333 and DUE/ATE 1502046.
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An ROV consists of many systems that are independently constructed and then assembled into a single ROV. The frame, power, controls, propulsion, and buoyancy are the major systems. In addition, your ROV may have a number of other systems depending on it purpose and mission. Mission tools such as grippers, hooks, temperature probes, or sampling devices may need to be constructed. A camera can be added to the vehicle. All of these systems need to be integrated together into one vehicle. All of the systems are interconnected, altering one system may affect another system. For example, adding more manipulators may mean adjusting buoyancy. You will also need to adjust your frame to hold additional tools. The design of the control box influences the number of motors and the placement of those motors on the frame. You job is to combine all the ROV systems into an integrated vehicle to complete the task at hand.
Frame: A sturdy three dimensional structure that holds all the systems together.
Power: Provides the pathway for the electrical energy to get from the surface controller to the ROV.
Control: Allows the ROV pilot to control thrusters, tools, cameras, lights, and other subsystems on the vehicle.
Tether: Transmits data and power between the vehicle and the controller on the surface.
Propulsion: Provides the force to move the ROV through the water.
Buoyancy: Adjusts the tendency of the ROV to float or sink.
Mission Tools: Grippers and sensors to achieve the mission tasks.
30 min to 2 hours
PVC pipe, connectors or other material.
The ROV frame is a sturdy three dimensional structure that holds all the system components together. Before building a frame, the MATE Center recommends taking time to sketch an initial frame design or build a model of the frame (cardboard, pipe cleaners, or computer drawing tools) to get an idea of the basic shape and where equipment will be placed. Consider where the motors will be mounted, if tools or cameras are going to be attached, and what the ROV is designed to do. Frame designs often go through four or five iterations to get it exactly right. Therefore it helps if the frame is modular or can be easily changed to incorporate new designs.
PVC is often used as the material to construct a frame. PVC is cheap, easy to work with and is readily available in most hardware stores. PVC comes in many sizes, measured from the inside diameter of the pipe. ½-inch pipe is the smallest, commonly available size of PVC, but ¾-inch, 1-inch, 1 ¼-inch and 2-inch are also readily available at most hardware stores. 3-inch, 4-inch, 6-inch and larger diameter pipe is much more difficult to find. The other benefit of PVC is the many different connectors that are available. Tees, 90 elbows, 45 elbows, sideout corner pieces, crosses, couplings, end caps and more. Reducer bushings that connect two different sizes of pipe are also available. PVC pipe will allow almost any shape and size of frame.
Different PVC joints
Other Frame Materials:
A frame can be made out of any material. Professional ROVs use aluminum or even titanium for the frame. Aluminum and plastic sheeting are common frame materials as well. Use whatever works best for creating your frame.
A plastic frame ROV.
There is no set MATE frame design. Building a frame depends on the tools and other systems that are going to be incorporated into the frame, and the tasks that the ROV will be required to do. MATE does have some guidelines to help when building a frame.
Colored PVC pipe.
Fun Frame Designs:
PVC can be painted. Alternatively you can buy colored PVC pipe and connectors, generally called Furniture Grade PVC. You can find colored PVC at: www.simplifiedbuilding.com/blog/color-furniture-grade-pvc-fittings-now-available/
Colored PVC is quite a bit more expensive, and usually needs to be screwed together as opposed to only pushing together by hand. However, it can really enhance the way an ROV looks.
Another option is to run the motor wires through the frame of the ROV. This keeps the wires out of sight and out of harm’s way, and they emerge from the vehicle frame at a single strain relief point. To run the motor wires through the frame, drill a 3/16-inch hole through the ½-inch portion of the motor mount. Push the wires through this hole and work them through the framework of the ROV, and out through the strain relief. Note that if you are using screws to hold the frame together, buy short, ⅜-inch screws. Otherwise the points of the screw can damage the wires inside the PVC pipe.
Take all the necessary precautions when cutting PVC pipe to ensure a safe experience.
Additional information can be found in the Frame Design Presentation here:
PRESENTATION LINK: FRAME DESIGNS
Wire strippers, soldering iron, solder, hot glue gun and heat gun
Red/black power wire, in line blade fuse holder, power-pole connectors, hot glue and heat shrink
The power system delivers electricity to the control box, which is then delivered down the tether to the ROV. The 10 or 15 amp blade fuse protects the electronic systems. The powerpole connectors connect to a power source and help to prevent polarity mistakes (connecting red/positive wires to black/ground wires). The AngelrFish Power Kit comes mostly assembled. The Powerpoles are already connected to the ground wire and the fuse wire. The fuse wire must be connected (soldered to) to the red power wire. Although this connection should never be underwater, it is a good idea to waterproof any solder joint you make on an ROV. The other end of the wire will be connected into the control box. To create your power system wires follow the instructions found here:
PRESENTATION LINK: POWER SYSTEM: CREATING YOUR POWER WIRES
Important note: Attaching Anderson Powerpole connectors to the wires REQUIRES a special crimping tool. If you are attaching your own powerpole connectors to the wires (not required for the SeaMATE AngelFish ROV kit), do not use a standard crimper to make these connections. Standard crimping tools are not sufficient to make a proper connection on the Anderson powerpoles. In 2017 Anderson Powerpoles will be required for all teams competing in the MATE ROV competitions. To learn more about Anderson Powerpoles please go to: http://www.marinetech.org/anderson-powerpoles/
Creating the power wires requires soldering two wires together. If you are unfamiliar with soldering,
The MATE AngelFish kit does not come with a power source. You will need to provide a power source to power your vehicle. The SeaMATE store offers three different solutions, depending on your budget and how you intend to use the ROV.
Power pack with powerpole adapter:
Powerpacks are battery packs that will provide the power you need. They are often kept in vehicles to jumpstart a car battery if there is a problem. They will run down over time, but can be recharged easily by plugging them into a wall socket. A standard power pack should be able to run a PufferFish ROV for 1 to 2 hours.
The power packs will need an adapter for the powerpole connector to plug into. This adapter plugs into the cigarette lighter outlet found on the powerpacks, and the Powerpoles plug into the adapter. The cigarette lighter adapter can be purchased from the SeaMATE Store at:
12 volt Deep-Cycle Marine/RV car battery:
Large lead acid batteries are another way to power the ROV. MATE recommends the Deep-Cycle Marine / RV battery, as they are designed to be run down and recharged many times (a standard 12 volt car battery is not designed for this). The battery should be able to run a PufferFish ROV for 4 to 6 hours or you can run 3 ROVs at a time for an hour or more. The battery will need to be recharged after that. To recharge a car type battery, you will need to purchase a charger.
The battery will also need an adapter for the powerpole connector to plug into. This adapter has Alligator clips that connect to the battery posts on one end and has powerpole connectors at the other end. The alligator clip adapter can be purchased from the SeaMATE Store at: http://seamate.myshopify.com/collections/all-products/products/alligator-clips-to-powerpole-connector
AC to DC Power Supply:
For a solution that never needs recharging, the MATE Center recommends an AC to DC, 30 amp power supply that plugs into an AC outlet, and provides a constant source of 12 volt DC power that the ROV needs. This power supply can operate two AngelFish or PufferFish vehicles at once without issue.
SAFETY NOTE: Since this converter is being used near water, you MUST plug this converter into a Ground Fault Circuit Interrupter (GFCI) protected outlet, or have a GFCI plug on the end of the converter. DO NOT PLUG THIS INTO A STANDARD WALL SOCKET WITHOUT GFCI PROTECTION.
MATE also recommends keeping the AC to DC converter in a splash proof container or case. A small plastic tub turned upside down will work to keep splashes off the power supply.
You can purchase the 12 volt power supply (sold together with a GFCI) from the SeaMATE Store at: http://seamate.myshopify.com/collections/all-products/products/12v-dc-power-supply-w-powerpole-outlet-gfci
1 to 2 hours
Wire cutters, wire strippers, crimping tool, Phillips head screwdriver, ⅛ inch flat head screwdrivers, utility knife, pliers, ruler with metric scale.
AngelFish ROV kit
The AngelFish control system links the power system and the propulsion system. The control system uses three double pole, double throw rocker switches. These switches allow the pilot to turn the electricity to each motor on and off, and also control which direction the motor turns in (forward and reverse).
To build the AngelFish control system, follow the AngelFish Control System instructions found here:
PRESENTATION LINK: CREATING THE ANGELFISH CONTROL SYSTEM
Understanding how a double pole, double throw (DPDT) switch works is key for understanding the control system. MATE recommends reviewing how a DPDT switches operates; this is key for understanding how your AngelFish kit works. You can do some hands on exercises with the SeaMATE Simple Circuit Kit. With this kit, you can play with switches and learn how a switch controls a motor using the How Switches Work worksheet. You can also view three short videos about how a DPDT switch works, and how three switches work together in your control box. You can find this additional information at the links below:
WORKSHEET LINK: HOW SWITCHES WORK
Video 2A: BASIC CIRCUITRY WITH A DPDT SWITCH
Video 2C: THREE SWITCHES CONTROLLING THREE MOTORS
15 to 30 min
Wire strippers, soldering iron, solder, hot glue gun and heat gun
Tether wire with six 18 gauge wires (black, white, green, red, blue, and brown)
The tether system connects the control box, which is on the surface, to the ROV, which will venture underwater. The tether should have two wires for each motor; one carrying power to the motor and one carrying it back to complete the circuit. Since the AngelFish has three switches controlling three motors, the tether providing power to the motors will have six wires. Your tether may include other wires, cords and cables as well. If a camera is used on your ROV, there will be an additional camera cable in the tether. The camera cable will have two wires to provide power to the camera, and additional wires for the data (video signal) coming from the camera. The camera wires are usually all wrapped into one cable. If you are building a hydraulic or pneumatic manipulator, the airline tubing will be part of the tether. Other systems, lights and sensors, may require additional cables as well. Remember, although it may be nice to have lots of systems on the ROV, each system needs wires or lines, and each wire adds thickness and mass to your tether. If there are too many systems on a small ROV, the motors may not be able to push the big thick tether through the water.
If you do have two or more lines running through the tether, it may be ideal to wrap your tether in a sheathing. The AngelFish kit does not come with this sheathing (it really isn’t needed since the AngelFish only has one cable with six motor wires) but tether sheathing is available for purchase from MATE. The Tether presentation shows how to wrap your tether in sheathing. Remember! Wrap your tether BEFORE making the soldering connections on either end. It is very difficult to impossible to do afterwards.
PRESENTATION LINK: INSTALLING A SHEATH OVER YOUR MULTIPLE TETHER WIRES
Length of tether: Why don’t we build our small, 12 volt ROVs with 32 meters (100+ feet) of tether so we can explore in a greater area? Why not 150 meters (500 feet) of tether?
Longer tethers have issues. It takes a little bit of voltage to push electricity through every bit of wire you have. As you increase the length of wire, you decrease the amount of voltage that you are getting at your motor. This is called voltage drop. Since electricity must run through a circuit (from the battery to the motor and back to the battery) every 0.31 meters (1 foot) you increase your tether length, the electricity now has to travel 0.62 meters (2 feet) more in distance through the circuit. All that distance can add up. As your motor sees less voltage, it won’t turn as fast. That means you have a lot less thrust. At 8 meters (25 feet) of tether, the motors work well and provide plenty of thrust. At (10 meters) 33 feet, they still work well, but don’t provide quite as much thrust. At 13 meters to 16 meters (40 or 50 feet) you will really notice the drop in motor thrust. At 33 meters (100 feet) of tether, your motors will likely not provide enough thrust to move your vehicle through the water. There are many online tools to calculate voltage drop.
Check out the following online calculator.
Wire is copper or aluminum wire.
Wire size is 18-gauge (AWG).
MATE ROVs use 12 volts DC.
MATE ROVs use single sets of conductors.
In water, our load current is approximately 2.5 amps.
Think about some of the things that could be done to increase the voltage at the bottom end of the tether.
Attaching your tether to the control box:
This section deals with attaching the top end of your tether into the control box. The next section, Propulsion, deals with attaching motors to the bottom end of your tether. To connect the top end of the tether, follow the instructions found here:
PRESENTATION LINK: CONNECTING THE TETHER TO THE CONTROL BOX
The Propulsion System
Loctite thread lock, small hex wrench (included in kit), and Phillips screwdriver
PufferFish Motor and Propeller Kit
The propulsion system consists of the motors, propellers, motor couplings and the tether management cross. The wires from the three motors connect to the bottom end of the tether. There are three sections to creating the propulsion system, each with its own instructions. Creating the tether management cross MUST be completed before connecting the motor wires to the tether.
Attaching propellers to the motor
Your PufferFish Motor and Propeller Kit comes with three bilge pump motors, three PVC motor mounts and three propellers with attachments for each. The propellers need to be secured to the motors at the end of the motor mount. Loctite (metal glue) will help to secure the propellers onto the motor and keep them from falling off when moving through the water. To attach your propellers to your motors, follow the instructions found here:
PRESENTATION LINK: PROPULSION SYSTEM: MOTORS AND PROPELLERS
Creating the tether management cross
Not having any strain relief on the bottom side tether can cause problems. Any tug on the tether will pull directly on solder joints and could cause issues. Having loose wires on the vehicle side near the might cause issues too. Loose wires can get pulled into propellers and be damaged, or damage the propellers. The MATE PVC strain relief allows the wires to be tightened and secured against strain damage. Using ½-inch PVC allows the strain relief to be incorporated into an ROV frame made from ½-inch PVC pipe.
Note: If you are using ½-inch PVC pipe for your frame, take into account the cross in the tether management system. If you are not using ½-inch PVC pipe, you will still need to take strain relief into account when building your ROV. To build your strain relief, follow the instructions found here:
PRESENTATION LINK: PROPULSION SYSTEM: CREATING THE TETHER MANAGEMENT CROSS
Connecting the tether to the motors
The final step in adding your propulsion system to the ROV is to attach your motors to the bottom end of the tether. Make sure the color combinations you used on the topside of the tether (tether wires going into the control box) match up with your bottom side tether (which color wires go to which motor). If you use the MATE color scheme (recommended), the red and green wires should go to the left switch in the control box and the left horizontal motor on the ROV. The black and white wires should go to right switch in the control box and the right horizontal motor on the ROV. The blue and brown wires should go to the lower, middle switch in the control box and the vertical motor on the ROV.
Since these wire connections are going underwater, make sure to use hot glue and shrink wrap on every joint to ensure a waterproof seal. If you need additional practice, see the presentation on SOLDERING WIRES AND WATERPROOFING CONNECTIONS and the corresponding MATE SOLDERING WORKSHEET.
To connect your motors to your tether, follow the instructions found here:
PRESENTATION LINK: PROPULSION SYSTEM: CONNECTING THE TETHER TO THE MOTORS
When you have completed all of these steps, close up your control box and attach your motors to your frame.
Congratulations, you have an AngelFish ROV!
Reusing the AngelFish ROV Kit
The AngelFish kit was designed to be a reusable learning tool year after year. The control box is easy to disassemble to its basic components. Only a few components have to be discarded, the wires and terminal ring connectors on the back of the switches and tether. An AngelFish replacement kit replaces the discarded wire and terminal ring connectors, allowing the majority of the kit to be re-used in subsequent semesters or years. To disassemble the AngelFish control box:
The AngelFish control box refresh kit includes new 100 cm (40 inches) of 18-gauge wire to construct the X’s and power jumpers on the back of each switch, and 34 new terminal ring connectors (28 red, 6 blue) to crimp on the end of the wires. These replacement parts can also be purchased at most hardware stores.
Other steps of the ROV construction process can also be disassembled by cutting wires. This will allow other ROV construction processes to be completed in the future.
The three motors may be detached at the bottom end of the tether by cutting the wires. Cut the entire soldered length of wire, underneath the waterproofing shrink wrap, out of the wire. Note that cutting the motors means a loss of 2 cm or 3 cm from both the tether wire and the motor wires.
30 min to 2 hours
Hacksaw or scissors
Foam flotation or larger diameter PVC pipe.
In most cases, you want your vehicle to be as close to neutrally buoyant as possible. A neutrally buoyant vehicle will neither rise nor sink in the water. If motors are not running, it will stay where it is in the water column. Large work class ROVs and other vehicles that go into the ocean or other environment are usually slightly positively buoyant. That means they slowly rise if motors are not driving them down. A slightly positive ROV in the real-world environment has a few advantages. If the tether gets completely cut, a slightly positive ROV will come back to the surface where it can be recovered. Also, ROVs operating near a muddy bottom don’t want their thrusters pushing water down (thrusting the vehicle upward to compensate for negative buoyancy). That thrust will stir up the bottom mud and can make it impossible to see. The MATE Center recommends making a vehicle that is slightly positively buoyant if you plan to use it in the ocean or in a lake and neutrally buoyant if you are using it in a pool. A neutrally buoyant ROV is easier to operate.
Buoyancy and Ballast
Buoyancy is considered to be all the components that are less dense than water and will cause a vehicle to rise towards the surface when in the water. Ballast is considered to be all the components that are more dense than water and will cause a vehicle to sink towards the bottom when in water. In most cases all the components of your ROV will be ballast. PVC in the frame and motors are the main sources of ballast in an ROV. Most often, flotation will be needed to offset the weight of the other components of your ROV.
The tether can be a source of ballast as well. ROV teams may want to consider adding buoyancy every meter or so along their tether to offset its weight.
A lot of math and science goes along with trimming your ROV (i.e. adjusting the buoyancy, ballast, pitch and roll of the ROV.) You can learn more about buoyancy here:
PRESENTATION LINK: GENERALl BUOYANCY CONCEPTS
ROV Buoyancy Choices
There are a lot of different types of flotation that can be used in an ROV. A few different types are presented here, but be creative. You may find another buoyancy solution works best for you. There are lots of different ways to add buoyancy to your vehicle.
Soft Foam (Pool noodles or pipe insulation foam): Pool noodles are soft, colorful foam that is fairly inexpensive and can be found at many local big box stores (Walmart, Target, etc.). Pipe insulation foam is soft foam that is designed to fit around PVC and other pipes. It is fairly inexpensive and can be found at Home Depot and other hardware stores. Both of these soft foam options can be cut with scissors and is very easy to work with. However, there is a drawback. Soft foam is soft. Soft foam will compress at depth as water pressure increases. It is generally okay down to 1.5 meters, but as an ROV descends deeper and deeper, the foam will compress and lose its buoyancy. At 3.5 meters (12 feet), soft foam loses about half to two thirds of its buoyant property. Vehicles with soft foam at this depth can lose so much buoyancy from pressure that the motors can not longer return the ROV to the surface.
Larger Diameter Capped PVC: 2-inch, 1 ½-inch and other larger diameter PVC, with air inside, and with end caps glued to each end can also be used for flotation. The volume of air inside these rigid pipes provides a good amount of buoyancy. These pipes will not compress at pool depths, but do be careful if you plan to go beyond 20 or 30 meters. You may want to test your canisters to these greater depths before taking your ROV there. Using larger diameter pipe also allows you to use math to calculate exactly what lengths of pipe you will need. See the section below on how much flotation you will need to make your vehicle neutrally buoyant.
Rigid Bouyancy: Rigid buoyancy is harder foam that can be shaped and can go down to much greater depths than soft foam. There are various types of rigid buoyancy foam, often times defined by its depth rating. For a very high price, you can purchase syntactic foam that is rated to 4000 meters, but in general, you can find less expensive foam for the depths you may be going to. Home Depot and other hardware stores have architecture foam. It is a rigid foam that can be cut with a knife, saw or box cutter. Surfboard foam is also dense and can be coated in epoxy resin to keep the water out. You may find other sources of harder foam or rigid buoyancy that you can use to go deeper. Again, be creative and you might find a unique solution for your buoyancy.
How much flotation will you need to make your vehicle neutrally buoyant?
Your ROV will not be neutrally buoyant and will most likely be negatively buoyant in water. Use a fish scale or spring scale to weigh your vehicle in water. Tie ropes or string to your vehicle, dip it so the ROV is completely underwater, then measure the weight. Make sure to keep your spring scale above the water, especially if it is an electronic scale. This will tell you the weight of your ROV in water (sometimes referred to as Wet Weight). Now you can calculate the amount of flotation you will need to offset this weight.
Air essentially weighs close to nothing (for our our calculations here). So one cubic centimeter of air has a weight of 0 grams. One cubic centimeter of water weighs 1 gram. In water, one cubic centimeter of air will provide 1 gram of positive buoyancy. If your vehicle has a wet weight of 600 grams in water, you will need 600 cubic centimeters of air to offset that weight. (Remember to take into account the weight of the foam or cylinder you will be using, you need something to “enclose the air” and that something will have a weight.)
If you plan to use larger diameter pipe as flotation, you can calculate how much pipe you will need to offset the weight of your vehicle in water by doing buoyancy calculations. You can find out more here:
PRESENTATION LINK: BUOYANCY CALCULATIONS
The final slide of this presentation has the Net Buoyancy for 1-inch pipe, 1 ¼-inch pipe, 1 ½-inch pipe and 2-inch pipe. You should verify these numbers yourself before calculating the length of pipe you will need.
November 1, 2017: Updated link to General Buoyancy Concepts. MG
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