Intro: Underwater ROV
This instructable will show you the process of building a fully functional ROV capable of 60ft or more. I built this ROV with the help of my dad and several other people who have built ROVs before. This was a long project that took al summer and part of the beginning of the school year.
Step 1: Design
In order to keep the ROV stable in the water, you need a design that is weighted on the bottom and has floats on the top.
The first ROV was built by Steve of Homebuilt ROVs. His website has numerous ROV designs as well as links to other ROV websites. He also incorporates several How To instructions in his site. I found this site to be invaluable in building my ROV, and would recommend it to anyone interested in building their own
The second ROV was built be Jason Rollette at Rollette.com His design is a little different but still very effective.
For my ROV I decided on a large center tube with two smaller tube located on either side, slightly underneath the center tube.
Step 2: Frame
Here is the beginning of the frame I am building for the ROV. I cut plexiglas windows and sanded them to fit inside the pipe. This is Schedule 40 ABS pipe, commonly used for sewage. When joining this pipe, make sure you use solvent glue that is specifically made for gluing ABS. Normal PVC cement will not work or create a poor bond that could leak. I am also using a marine sealant to seal the plexiglas and prevent water from coming in. On the back end, I am using screw plugs in case i need to access the batteries or electronics again. I will need to wrap the threads in teflon tape to make it water tight.
After some testing, I found that the screw plugs leak, so I switched over to rubber end caps that have a band clamp to secure them.
Step 3: Thrusters
One of the most important features of an ROV is movement. I found that most people use marine bilge pumps as a means of thrust. BIlge pumps have many advantages. They are meant to be submerged, they are fairly powerful and they are easy to add to an existing ROV. Most use them in their current configuration, but I opted to use propellers to increase thrust. I followed the instructions at Homebuilt ROVs. In the How To sections, he has instructions on converting a bilge pump to use a prop. The propellers came from Harbor Models, they have a good selection of plastic and some nice brass props, with many different sizes.
I used 4 Rule 1100 GPH bilge Pumps, 2 for forward, backward and turning, and 2 for up and down.
Step 1: Cut off all of the white housing of the bilge pump, but be careful not to cut into the red motor housing
Step 2: Use a screwdriver to pry off the impeller, the blue thing to expose the motor shaft.
Step 3: I use a prop adapter for an airplane to attach the propeller to the shaft. It has a set screw, and I just tightened the nut against the threaded hub on the prop to lock it in position. I had to re-thread the prop adapter because it was a little too big. As a extra precaution, i used thread locker to seal the assembly together.
Since the threads did not line up, I was forced to re-tap the prop adapter. Although it seemed straightforward, it took considerable time to do it correctly.
Step 4: Navigation
To determine which direction the ROV is facing, I used an electronic compass. This is a Dinsmore 1490 electronic compass. I got it from Zargos Robotics. I used this schematic to create a visual representation of the direction. One note: This compass has no North. You just select a direction as north, and then all the rest will line up. It is also very sensitive to tilt, a few degrees and it gets screwed up. It senses changes in Earth's magnetic field, so make sure you place it far enough away from magnets, like the ones in the motors. If you need more info about the compass, check this site out
In the picture, the four wires in the silver casing will go to the surface and interface with the computer to show me which direction I am facing. I am writing a program that will rotate an image of the robot to show direction. However, this might take a while so for now I might just use the LEDs
For a tilt compensated compass, check out this one at Sparkfun. It is definitely top of the line, but also carries a huge price tag
EDIT: I removed this because of its inability to maintain a steady heading. This is most likely due to the tilt that the compass couldn't handle, along with the magnieting interference.
Step 5: Camera
Obviously you need a camera to be able to see what is going on, right? There are several different ways to go when getting a camera. If you're planning on going pretty deep, then a black and white infared camera would be a good bet. For shallower water, color works just as well, plus it shows more detail (ie. color?). If you really want a good picture, then go with a dedicated underwater camera. These cost quite a bit more, but you don't need to worry about an enclosure, and they often switch to night vision automatically with built in IR illumination when there is not enough light.
I went with a 30$ color camera from Spark Fun. It has an RCA output that I will attach to my computer. Here it is attached to a mount ready to be installed.
The PC card connects to the camera via RCA, and also came with a program to view and capture the video feed
Step 6: Lights
I needed some lights that are fairly bright and also efficient. LEDs are exactly that, and I found some at Spark Fun Electronics. I used two 3 watt LEDs, and to be honest, they are blinding. They do get a bit toasty, so be sure to use a heat sink to prolong the life of the LED. Spark Fun sells an aluminum breakout board that has solder spots for wire and also acts as a heat sink. They have different LED colors too.
I attached the LEDs to a stand I made out of an L bracket to hold the in the center of the viewport. to make it easier to change, I bolted them to a aluminum strip so that they an be adjusted or replaced
The pictures do not show how bright these things really are. After looking for a second at one, I had spots in my vision
Step 7: Control: ROV Side
This is probably the most difficult part of the entire building process. I have seen numerous different approaches to controlling the ROV. Jason Rollette used a microcontroller, which is really the best way to go. He has full analog control of all motors, and at the data is transmitted up a Cat 5e Ethernet cable. However, unless you have the means to print out a circuit board and program a microcontroller, this is not the easiest to assemble. Jason has a diagram of the circuit and the PCB on his site here
Alternatively you could use relays to switch the motors on and off. this is not as good as full range control, but it is much simpler and straightforward. At Homebuilt ROVs, Steve used relays to control the Seafox, and he has a good guide to assembling any number of relay controlled motors.
This is one of the 4 speed controllers I am using for the thruster control
Step 8: Power
I decided to carry batteries in my ROV to make it more independent and reduce the number of cables going to the surface. This is one of two 12 volt 2.5 amp hour batteries I bought from Battery Mart. I have already wired it up to a Deans Ultra connector so it can be easily removed if it is needed. Due to the amp draw of the thrusters, I might need to incorporate a charging circuit to keep the batteries topped off. They will be carried in the two side tubes, and add much needed weight to the ROV
Step 9: Control: Surface
Now we enter the difficult realm of piloting. The two people I talked to use a laptop to control their ROV, using a keypad or joystick to move the ROV around. This is great because all you need is the ROV, the control cable, and your laptop.
I wanted full analog control with out using a microcontroller, so I decided on ESCs, Electronic Speed Controllers. These should be familiar to everyone who has a model plane or car. I needed reversing speed controllers, and stumbled across some at Bane Bots. They are plugged into the Reciever inside the ROV, and the antenna is attached to one of the Cat 5 wires. From there I used my Hitec Remote control with the appropriate crystal and frequency.
The light are controlled by a switch that is operated by a servo. The compass has yet to be set up, but I think I might just use a bunch of LEDs instead of trying to interface it with my laptop.
EDIT: I have since upgraded my control system using an Arduino microcontroller and a servo controller. I will post my results a soon as I finish sea trials.
Step 10: Tether
To connect the ROV to the controller, I am using 100 feet of Cat 5e Ethernet cable. It has 8 wires, which fit in with my plans nicely. I might add a second cable if I have more features I need to run, but for now it looks good.
This is plenum rated Cat 5, meaning that it can be pulled through walls using a fishtape. The covering is tightly shrunk and has a thin nylon cord inside that helps distribute the load over the entire cable. This makes it more durable and reduces that chance that I damage the cable from load stress.
I will need to add floats to the cable because it will probably sink due to its weight.
The connector I used is a Bulgin Buccaneer Ethernet connector. It makes it easier to transport the ROV by separating the cable and the robot. Bulgin tests their connector thoroughly, and this is supposedly rated to 30ft for 2 weeks and 200ft for a few days. As I am planning on going no more that 100, this is well within the limits.
Step 11: Testing
The first time the ROV saw water, I tested it in my uncle's pool. As was expected, the ROV was too buoyant. I have since added lead weights I purchased at a hunting store to add weight to the skids. Lead shot would have been preferable because it is finer and easier to use, but it is really expensive. The lead also allows me to adjust the ballast with a reasonable degree of precision in the event that I need to change the weight on the spot. The total required ballast was about 8 lbs, quite a load. The next test will be in another pool, and then its hopefully into a lake! If you plan on using this in salt water, it would not be a bad idea to rinse it off afterward to keep corrosion down.
I will try to post some videos in the near future to show how this thing works in the water