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Nøkken - ROV (Underwater Exploration Vehicle)
Nøkken - ROV (Underwater Exploration Vehicle)

Nøkken is a supernatural being that lives in small inland waters and is a shapeshifter. It tries to trick people into drowning, often by changing shape into a horse, which when mounted would charge into a lake and take you to the bottom with it. I've never liked water, and a certain illustration by Theodor Kittelsen came to mind when I saw the LEDs glowing.

Nøkken

Mark I

23rd August 2010
This project started about 8 months ago in January 2010, when I saw that a surprising number of people were making ROVs at home. Though very few had footage of anything interesting, it certainly proved the concept was viable. I've always been fascinated and fearful of the ocean, so this seemed a great way to explore the depths without having to personally go where the sun doesn't shine. I began researching, finding websites, designs which looked clever, and parts which would be suitable.

About a month passed, and I began programming the control board and PC interface. This consisted of an ATmega8 in the ROV and a VisualBasic program on the PC end. The end result was a control board with camera feed, PWM light control, forward/reverse of three motors, battery level monitor, temperature sensor and a leak detector. All communications to the surface are sent through a 4-wire cable (cat-5 paralleled at each end) and received by any PC with two USB ports and appropriate drivers. Camera feed is received using a 20$ EasyCap USB device, while the serial commands to the ATmega8 are sent over RS-485 thanks to an FTDI USB chip. Since both the camera and serial signals are USB compatible, any PC worth it's salt can be used to control the ROV.

Circuit lashup  Control Program

Camera feed is provided by a small PCB type composite video camera, just 30$ at Sparkfun. It's excellent at adjusting to various light levels, and works best in near darkness, which suits the ROV well. Lighting is provided by two 10W LEDs, though I will probably only need to run them at 20% duty, where they seem to give more than enough light for the camera. The circuit boards were put in tubs and submerged in hot wax, rendering them pretty much water tight in the event of a leak. The camera PCB was simply covered in RTV silicone, so it can withstand splashes at least. Most of the project time was spent creating this interface, despite it not seeming like a big job initially. The end result was worth it however, giving me a nice, reliable, solid state controller. Power for the whole assembly is  supplied by an 8Ah 12V SLA battery, on board the ROV.

Schematics, PCB files, source code, firmware and PC software can be downloaded here. (Updated 14.04.11)


Potting cirucit boards  Completed control boards  Waterproofed 10W LED

I had seen the "HomebuiltROVs" guy had made a slip-ring reel for his tether, and I thought something like that would be vastly more practical than throwing cable overboard and reeling it again by hand. Having waterskiied for some summers now, I knew that this would only result in headaches when it came time to untangle the mess, especially if the ROV couldn't be disconnected from the tether. A decent amount of woodworking went into the tether reel, and with two coats of varnish it should hold up to salt water splashes. The slip ring is a professional unit purchased on ebay, well worth the money. The electronics housing is simply an ice-cream container. Thrust is provided by four 360gph bilge pumps. I've modified them to use propellers, using some modified RC components (also from ebay). The connector used between the tether and ROV was some kind of marine connector purchased on ebay, from China. I wouldn't recommend it, as it leaks even at shallow depths. It did hold up long enough to test the ROV however.

Reel construction  Laptop interface circuitry.  Completed tether.
Axel fastened to pipe

The ROV itself was slapped together quickly compared to the rest of the project, taking only a few weeks. Basically it consists of a plastic pop-bottle crate, some drainage pipe and the duct-tape of the sea - zip ties. Some sawing, a little dremel work on the pop crate to make room for the pipe, some fine dremel work on the left-overs to make motor supports and the frame was done. Everything was zip-tied in place, which both fastens and allows for removal later. I was never able to make the ROV entirely watertight, and as the main chamber filled with water the ROV would begin to tip backwards. To counter this, I sealed an ABS pipe full of air and suspended the ROV beneath it, while placing weights on the bottom of the ROV. This keeps it stable even as the hull takes on water. Buoyancy and stability are important aspects of ROV design, and need to be taken into consideration. Otherwise your ROV might sink to the bottom, or simply point straight up like mine did before the fix!

Finishing the ROV  Front view of ROV  Almost complete ROV
The finished product!

Now, closer to the present I was actually able to take the ROV out for a dive in the ocean. Before this I had tested it in the bathtub a few times, and twice in a nearby lake. Neither provided any interesting to see, so I hoped things would be different in some clear ocean water. All in all, the ROV was out for about 30 minutes, but because of the camera angle (straight forward), there is only a few minutes of interesting footage. None the less, it's enough to make me eager to improve the ROV further, and hopefully take it much deeper. In the video below the ROV was driving near the surface down to about 3 meters at the most.



Parts and expenses
All told, this project set me back roughly 500 USD. To help anyone looking at making something similar I've listed some of the components I used and their cost at the time. Some can be found cheaper now, or better components are available for the same price. So be sure to investigate this for yourself! In addition to the components listed below, you'll need bilge pumps, several discrete electronics components, and of course some stuff from the local hardware store.

From Ebay, I purchased the following:

EasyCap RCA~USB 2.0 Video Capture/In, VCR/VHS~DVD maker 31,59 USD
2x 10W Power White LED Light Bulb 700lm 120 degree 24,00 USD
KYM06 Slip Ring (6 wires, 2 amps) 43,00 USD
4x Plastic Propeller Props, 3.18mm*35mm 8,93 AUD
5x Plane CNC Motor Shaft Prop Adapter 2mm to 3mm 2,99 USD
USB to RS232 Module Based TTL PC FT232R FT232 FT232RL 19,98 USD
USB Type A cable for FTDI 1.62 USD
USB extension cable 2.99 USD

Sparkfun:

Temperature sensor, DS18B20 4,25 USD
RCA Color Camera    CMOS Camera Module - 640x480 31,95 USD
2x Full-Bridge Motor Driver Dual 5,90 USD
2x Breakout Board for RJ45 3,90 USD
2x RJ45 8-Pin Connector 3,00 USD

Aftermath:
Even at the relatively shallow depths I had taken the ROV down to, a few centimeters of water had already collected in the hull. Upon disassembly of the ROV and inspection of the hull later, I've found a hairline fracture running lengthwise along the bottom of the pipe. This proves the PVC drainage pipe is definitely not pressure rated, and far too brittle for this application. The major problems so far have been water leaking into the hull, water leaking into the tether connector, seaweed jamming the propellers, and the tether itself sinking. The poorly chosen camera angle was a real bummer too. A note to anyone who none the less wants to use an unsealed hull solution, any water vapour trapped in your ROV will quickly fog up the interior. If your camera is too far away from the plexiglass face moisture will build up in front of the camera, ruining your camera's focus. Quite often I would bring the ROV up only to find the entire face had fogged over, except for a small hole where the camera was positioned. This is largely because the camera was spaced only a few millimeters from the plexiglass. Another problem I noticed was that the wax used to seal the motor driver actually melted and ran off. This left parts of the motor driver exposed to saltwater, which would have corroded it to pieces had I not discovered it when I did.

Propellors gunked with seaweed.


Mark II


Based on my experiences with the ROV this summer I plan to upgrade the ROV. It's already been disassembled, and with any luck I may be able to try it again before fall.

The plan is to seal all of the electronics, camera and wire connections in wax, that way leaving no empty space for water to leak into. I'm also looking at some IP68 rated connectors for the tether so it stops leaking and shorting out the control signals. I'm not sure whether I should leave the battery on board or not at the moment, but I'm quite tempted to leave it on land. By not having it on board the ROV I would remove the need for an openable, watertight container, which would vastly simplify waterproofing. On the other hand, I would need a new tether assembly, and heavy currents flowing beside the camera feed might introduce too much noise.

Update 15. Jan 2011
I did a bunch of work on the ROV during the fall, but needed some new parts which essentially stalled the project. Since the last update, I've decided to leave the battery on land, and run power through a long 14AWG marine rated cable. Load tests have shown a voltage drop of 1,60V when running all motors and  LEDs on 100% duty, which is acceptable. To accommodate the new tether setup, I decided to modify the existing tether reel rather than make a new one. The base was spun around 180 degrees, giving me just enough room to mount the battery. The hand crank was spaced far enough from the reel to allow me to install a slip ring, which this time I had to make myself. What I did was pull the main power wires through the pipe and place some plastic spacers between them. Once the wires were out and spacers placed, I soldered some brass strips to the wires. These strips were then wrapped around the pipe until tight, and finally soldered so they remained in place. That was not an easy job. Between the wire connection on the bottom, and the solder used to hold the strips together, they didn't turn out very round. Still, they are round enough to be used. With the wires brought out of the pipe, assembling brushes to make contact with them wasn't too difficult. Some enameled copper wire was simpled stripped and wrapped around the pipe, and fastened with springs to the reel.

slip ring construction  slip ring construction 2  New tether reel

With the new power source secured, I could reduce the size of the ROV. Since the ROV wouldn't need to be opened again anymore, I crammed all of the electronics into what used to be the camera/control electronics housing. The temperature probe was epoxied to the motor driver heatsink, so I know if it's melting wax again. Once everything was stuffed (literally, it was a damn tight fit) I tested to make sure none of the connections had failed. With all checks good, I could proceed to potting the entire assembly in wax. It took four large candles to fill the compartment.

Stuffed electronics compartment  New electronics housing  Hot wax in electronics
Solid wax  Wax face

As you can see the new ROV could be built very small, but at the expense of stability. I decided to use the same body as before, the old pop crate, and simply adjust the weight/floats according to the new layout. Taking wisdom from the last ROV, I mounted the camera so it would actually see something without having to rest on the bottom. Update 25.03.11 I've made some propeller shrouds from 5cm diameter polypropylene pipe, and mounted the new waterproof contacts. The main power connector is a 2-pin Standard Buccaneer from Bulgin, and the data connector is from Switchcraft. Next up I have to get some plastic mesh to keep seaweed out of the propellers, and then work on getting the buoyancy of the ROV just right. After that it should be ready for test run, once the lake here thaws.

ROV body construction  ROV body construction  Propellor shroud  
Completed Mark II ROV Upgraded tether

Update 14.04.11

The mark II upgrade has now reached the point where it's ready for a test run. In the image above you can see that I've mounted the same ABS float used in the Mark I ROV. Some iron scrap was required to ballast the ROV, but not as much as previously. With less ballast, and no battery on board the ROV is considerably lighter. Hopefully not so light that the heavier tether becomes an issue. While testing the ROV in my bathtub, I discovered all the motors had been reversed some time during reassembly. To fix this, I've upgraded the control center software for windows. You can now invert the steering, forward/reverse and ascend/descend, or both at once. COM ports can now be typed in as well, allowing port numbers higher than 20 to be used. The communications protocol used is the same as before, so the new software can be used with the old ROV board (which hasn't been changed).

Update 30 July 2012
Testing was preformed with Nøkken MKII last summer, but I wasn't able to document it until now. When actually attempting to use the ROV, communication would always time out, and the video feed would cut in and out (mostly out). It seemed the communications line had a break somewhere. With no control of the ROV thrusters, limited video and no means of field repair, I decided to sink it to the bottom and bring it back up again. If nothing else, it would provide some insight on how well the waterproofing worked. Despite the poor video connection some interesting video was recorded, which was enough to keep my interest in the ROV going. This summer (one year later) I decided to dismantle the ROV and see what went wrong. It turned out small fissures had devloped in the hardened wax, which allowed water to seep along the wires and into vital circuitry causing corrosion of the circuit boards. Some of the corrosion likely originated from the very first iteration of the ROV, where wax was also used to seal the circuit boards. Somehow a large air pocket had also developed while the wax was cooling, and this was partially filled with seawater even one year later. Strangly enough the corrosion alone didn't seem to be the real cause of the ROV failing. Instead the 5V regulator (which was foolishly soldered to wires and put on an external heatsink) had one loose wire, which would have disabled both the control circuitry and camera! Regrettably I didn't try the circuitry to see if it was still functional, but I did remove the ATmega8 and MAX485 ICs, both of which functioned. Later testing while building Nøkken MK 3 revealed an unforeseeable event, which would have made communication impossible even if the electronics hadn't failed. The program used to control the ROV relies on the .NET framework, which Microsoft released an update for. The "update" causes the serial port to misbehave, so when attempting to send information and then using RTS to go into read mode, the serial port instead goes to read mode before sending the data. This means the PC would request sensor data and go into read mode, however the ROV would never receive the message and also stay in receive mode! Needless to say the update meant the control software and possible ROV firmware had to be rewritten.

Based on these experiences, I began work on what I hope to be the final iteration of Nøkken ROV, the mark 3.

Did this project whet your appetite for ROVs? If so check out these links, and you'll be building one in no time.

Links:

Homebuilt ROVs
Jason Rollette's ROV
Submarineboat.com
ROV submersible (PVC) on Instructables
Underwater-ROV on Instructables
Swedish DIY ROV
Remotely Operated Vehicle T-bot
Engineering Projects - Remote Operated Vehicle (ROV)
German ROV (pretty proffesional)
The Sea Lion
JAWSS
Tiny German model ROVs, maybe for an aquarium
XKCD's ROV





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This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.

Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.