Instructions for the SeaMATE AngelFish ROV Kit

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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.  

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. 

AngelFish ROV Systems

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 its 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.  Your 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.  

The Frame

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.  

Using PVC:  

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.

Frame Design: 

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.  

1. Bigger is not always better.  With a set amount of thrust, a bigger frame will move and turn more slowly, while a smaller frame will move and turn more quickly.  Which is better?  It depends on what the ROV is doing.  Sometimes slow is better.  Consider what your ROV is going to be doing and design accordingly.  
   
2. Let water flow through the frame.  Don’t plan to use the air inside the pipe as buoyancy.  It is too difficult to prevent the air inside the pipes from leaking out, and then the buoyancy is lost.  The water inside the pipe is also mass, which must be pushed around by the motors.  Consider using tees at the corners so water can flow through the pipes.
   
3. Build a symmetrical frame.  If a 12 cm length of pipe is cut for one side, a 12 cm length of pipe will probably need to be cut for the otherside.  This is not always the case, but is a good rule to follow.  Not doing this can lead to a PVC frame that does not fit together well and breaks apart too easily.  
   
4. Place things around the center of the ROV.  If the vertical motor is not near the center of the vehicle, the ROV may pitch (nose up, nose down) when moving up and down.  Heavier items should be kept below the center-point.  Light items (flotation) should be kept above the centerpoint.  Ideally the tether should come out of the top middle or top rear of the ROV.  
   
5. ½-inch PVC pipe inserts approximately 1.5 cm into a tee, elbow or other connector.  Plan accordingly.  Keep excess PVC to a minimum.  The purpose of the frame is to hold the other systems together in a functional spatial arrangement.  If a length of PVC isn’t needed, don’t insert it.  
   
6. Pushing the pipe into a tee, elbow or other joint by hand should be enough to secure the connection.  If the connection is still bad, look at the symmetry of the connecting pieces.  If necessary, use a small screw to hold the pipe together instead of PVC glue.  PVC glue makes a connection that is inflexible, brittle and prone to breaking.  

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.

SAFETY:

1. PVC cutters are very sharp.  Never put fingers inside the PVC pipe when cutting it.
   
2. A small end of the PVC pipe can fly off when cut.  Wear eye protection when cutting PVC and make sure there is a shield to block any flying PVC from impacting others.  
   
3. Never cut PVC pipe at an angle.  This can cause the metal blade on the PVC cutters to break.  
   
4. Old PVC that has been in the sun gets brittle and has a tendency to crack and shatter instead of cut cleanly.  

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

The Power System

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 AngelFish 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: SOLDER AND SEAL CONNECTORS

PRESENTATION LINK: POWER SYSTEM:  CREATING YOUR ANGELFISH POWER WIRES USING SOLDER AND SEAL CONNECTORS

Do you want to practice using solder & seal connectors before using them on your ROV?  See the SeaMATE Wire Soldering Kit.  It now comes with a yellow solder & seal connector included.

Older AngelFish kits may not come with a solder and seal connector.  Older kits will only have a length of shrink wrap (black)  included with the Power Wire kit.  For older AngelFish kits, either purchase your own solder and seal connectors, or use a soldering iron to solder and waterproof the connection.  

OLDER PRESENTATION LINK: POWER SYSTEM:  CREATING YOUR ANGELFISH POWER WIRES (SOLDER)

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; Anderson powerpoles are already attached), 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.  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/ 

POWER NOTE:  

The MATE AngelFish kit does not come with a power source.  You will need to provide a power source to power your vehicle.  Listed below are three different solutions for powering your ROV, 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 an AngelFish ROV for 1 to 2 hours.  

http://www.harborfreight.com/3-in-1-portable-power-pack-with-jump-starter-62306.html

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:

Powerwerx CigBuddy 12v Lighter Plug to Powerpole Adapter – SeaMATE 

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: Powerwerx Alligator Clips with ATC Fuse to Powerpole Connector – SeaMATE

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: Powerwerx 12V DC Power Supply w Powerpole outlet + GFCI – SeaMATE

Control System

The AngelFish control system links the power system and the propulsion system.  The control system uses three double pole, double throw 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:  

PRESENTATION LINK:  HOW A SWITCH WORKS

WORKSHEET LINK:  HOW SWITCHES WORK

SeaMATE STORE - Purchase Simple Circuits Kit

Video 2A:  BASIC CIRCUITRY WITH A DPDT SWITCH

Video 2B:  WIRING A MOTOR TO RUN IN FORWARD OR REVERSE

Video 2C:  THREE SWITCHES CONTROLLING THREE MOTORS

The Tether System

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.  

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 in this section.  But before completing this step, check out the optional tether wrapping information below.  If you choose to wrap your tether it should be done BEFORE connecting the tether to the control box.  When you are ready to attach your tether to the control box, follow the instructions found here:

PRESENTATION LINK: CONNECTING THE TETHER TO THE CONTROL BOX

OPTIONAL:  

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.  

OPTIONAL 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.  

http://www.calculator.net/voltage-drop-calculator.html

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.  

The Propulsion System

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 AngelFish Three 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 the 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.  Solder and seal connectors come with hot glue (and solder) inside the shrink wrap.  Alternatively, teams can solder the wires and waterproof them with hot glue and shrink wrap.  If you need additional practice soldering, 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 reused in subsequent semesters or years. To disassemble the AngelFish control box:

1. Remove the six screws from the back of each of the three switches (18 screws total).  Be very careful not to lose any of these small screws, as they are important.
2. Remove all the wires from the back of each switch.  MATE recommends saving a few of the wires that make the X on the back of the switch and a few of power jumper wires.  If too many mistakes are made in crimping the wires, these pre-made X’s and jumpers can serve as back up.
3. Cut the six terminal ring connectors from the end of the tether.  Cut as closely to the terminal ring connector as possible to preserve the length of the tether.  Note that with careful, close cutting, only 1 cm to 2 cm of tether will be lost with each re-use.  Discard the cut terminal ends.

4. Cut the two terminal ring connectors from the end of the power wires.  Again, cut as closely to the terminal ring connector as possible to minimize loss of wire.

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.

SeaMATE STORE - AngelFish Refresh Kit 

Optional:

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.

Buoyancy

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: GENERAL 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.)

Mission Tools

Mission Tools:  The mission tools for your ROV will greatly depend on the mission it is undertaking.  The mission may be part of the MATE ROV Competition, the SeaMATE Spanish Galleon mission, or some other mission you want to undertake.  You can find out more about potential missions in the ROV mission presentation.  

PRESENTATION LINK:  ROV Mission 

The most simple mission tools are static, non-moving manipulators.  Another option is to add simple hydraulic manipulators that will open and close using a syringe on the surface connected to a syringe on the bottom.  Pushing the syringe on the surface will open a syringe on the ROV.  The movement of the opening syringe can be used to operate a manipulator.  As ROVs become more advanced, powered hydraulic or pneumatic systems can be designed.  Additionally, electrical motors can be used to open and close claws or other devices.  How you accomplish your mission is up to your imagination.

PRESENTATION LINK:  Non-moving Manipulators

PRESENTATION LINK:  Hydraulic Manipulators

Updates:

November 1, 2017:  Updated link to General Buoyancy Concepts.  MG

October 7, 2020:  Updated with new links to new presentations.  MG.

October 26, 2020:  Updated Buoyancy Section.  Added Mission Tools section.  MG.