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Submersible ROV

Submersible ROV

(OP)
Hello Gents. First off i'm new to the forums! Glad to be here, some reading through existing content tells me i'm in the right place. Next a bit about myself. I'm extremely ambitious! I live in Wisconsin. I love the outdoors i'm just afraid life doesn't allow me to experience it all that often. I'm the type that can sit in google earth for hours just exploring places i'd like to visit.

I've made a few attempts at exploring the world through remote technology recently. POV setups for the first time give the average consumer the ability to experience this. I'v always wanted to do what has not been done before and that brings me to my main topic for posting in this sub-forum.

As of recently i'v gained extreme interest in our oceans floors. The place we've only explored less than 5% of right? It's the most mysterious place on our planet. And so i would like to be able to endure a massive undertaking. I find when looking for help or guidance, its best to make your goals clear. It helps reduce guess work, assumptions, etc.

GOALS
-----

1) Engineer a submersible craft that can withstand extreme pressures of the ocean (5000+ PSi)

2)Be able to sustain dives for weeks or more.

-I have a clever power storage system in mind

3)Controls -Autonomous

I have a system that could do basic control via sat uplink. Also have a system that could do cellular, although cellular likely will not work in most ocean regions. My thoughts on getting the satt comm to surface is a deployable antenna. Most of the control itself would be autonomous.

4)Ballast.

This in lies most of my knowledge short-comings. I'm having a really hard time figuring out how i could design a ballast system that will fight 5000 psi water pressure. I bounced a few ideas around in my head on how this could work. I'v contemplated a mechanical advantage screw style (issue with sealing + a ball-screw strong enough) , a hydraulic powered piston (same sealing issue), a pump capable of displacing the ballast water, then simply an air tank that provides make up air to avoid vacuum build up. Last option i had was an air system strong enough to displace the water straight up. I'v done some research and it appears the technology does exist. The largest issue i have here is the volume required for displacement. Using Boyle's Law i calculated 5 gallons of displacement @ 5000 psi. IE 41~ lbs of ballast water. What I come up with is a 5 gallon cylinder filled to 5000 psi is roughly 227 cubic feet of air at atmospheric pressure.

Here is where I get lost.

Lets say i have a ballast tank that is more or less the outer hull of my craft. It has 5 gallons of storage. The outside water is a whopping 5000 psi static force. Do i understand pressure correctly when i say i need 5000 psi air pressure to defeat the water pressures? Do inlet/outlet sizes of the ballast affect the water pressure?

If i understand this correctly... psi works as a uniform static force underwater? IE if i had a plate on the hull of the craft that was 4" x 4" totaling 16 in2, @ 5000 psi the total pressure/force on that plate would be 16(5000)= 80,000 lbs of force?

Thanks for any input guys!

RE: Submersible ROV

Yes, pressure is everywhere and in all directions and has no respect for orifice size unless it is moving. You have to take a diving class! You will get all this hands-on.

ps: with the new waterproof cells, are they as common below as above? (I don't dive anymore)

RE: Submersible ROV

(OP)
ps: with the new waterproof cells, are they as common below as above? (I don't dive anymore)

I can't wait to take a diving course. Hopefully this year ill get down to florida and actually make it happen! Though i could probably still take a course here!

As to your PS. "New waterproof cells" ? I don't follow, what are you referring to?

RE: Submersible ROV

(OP)
I'm assuming you are referring to cellular. I wouldn't use cellular unless i was close to shore-line and able to grab signal. But even then, water is far too dense to transmit RF. My theory was to have a deployable antenna. A bouyant platform more or less than can detach from the sub, float to surface, and when needed, tow rope back down. Also its possible i can upload/download in-between dives, but its my goal to keep those as infrequent as possible (to prevent looting or vandalism of the craft, i see that being a large issue).

RE: Submersible ROV

Why don't you shoot a resume to Scripps Oceanographic here in La Jolla? I think they do your kind of stuff. I've designed piers and things for them as a consultant and, well you should see their facilities!

On rereading your original post, why aren't you on your way out here right now? Diving schools all over here. Good beer, too.

RE: Submersible ROV

(OP)
I checked it out! It looks absolutely amazing! Unfortunately I don't think wife is too keen to leaving Wisconsin :(

I have friends who live in Sacramento though so i'm really trying to make it out there soon!

RE: Submersible ROV

(OP)
Hello IRstuff, and thank you for the response!

It certainly was my plan.

The controlling devices were going to be a set of arduino's. One self sufficient system for automatic control, and another device in place for somewhat of an emergency mode or failure mode should it occur (it will). That been said, here is the satelite comm device/shield i plan to use in correlation with the arduino that will handle the comms.

https://www.sparkfun.com/products/13745

It is a very small device capable of connecting to the iridium network. Communication is somewhat limited and crude. From what i understand i would only be capable of sending limited data. Therefor the plan for the sat network is more or less to check diagnostics. Potentially make slight project changes. It certainly wont be video capable. The only option for a video feed would be cellular, where available. Though i did plan on having an on-board camera system capable of recording real time events. It would be limited to storing that data though. Unless i can find a nice place to surface, charge, and upload via cellular. I could see surfacing for an entire day to charge at times. Depends on a few factors i haven't yet set in place.

I digress. Do you see an issue with spooling that much wire? I am aware that once my platform hits the surface, it will change the buoyancy of my craft and will need to adjust ballast on the spot to maintain depth. The same for pulling the platform back down.

I guess the best cable for tow itself would be kevlar rope. Smallest most flexible rope i can get that will have the strength per volume. Expensive. But possible no?

RE: Submersible ROV

If I understand correctly, you're trying to work out how to flood then blow the entire hull volume.

I can't work out why you should ever need to do this.

Among the basic principles of submarine design...

1. You need to scale things so that, at the surface in the diving state, displacement and mass balance each other out to create neutral buoyancy. If the craft is to have an independent existence as a habitable surface asset, you will need a means of adding additional surfaced buoyancy, but I don't think that matters in your application.

2. You need to provide ways of compensating for changes in mass - or to limit mass changes. If you were thinking of lobbing off 60 tonnes of guided missile, then (as well as attracting unwanted attention), you would need to be able to make large rapid ballast adjustments. Your reelable buoyant aerial might be a bit of a luxury in this regard (would it be simpler for the whole boat to return to the surface to talk to the satellite?). Be aware that, at 5000 psi, 5 gallons of air weighs about 15Lb.

3. You need to provide ways for compensating for changes in volume - or to limit volume changes. The biggest issue here is compressibility and your aim should be to eliminate it where you can and only compensate for it where you can't. Airspaces exposed to ambient pressure are horribly compressible so any system that relies on an air/water interface to maintain neutral buoyancy is going to be naturally unstable (requiring active control/expenditure of air to avoid an uncontrolled rush to the surface or to crush depth). If you can fill voids with low density liquids rather than air, you will vastly reduce your need to compensate for buoyancy changes due to depth (Trieste used around 70 Tonnes of petrol for buoyancy - yet another way of attracting unwanted attention in today's MARPOL-aware world).

Once you've done everything you can to make your mass constant and to reduce compressibility, you should be able to calculate how much buoyancy variation you actually need to be able to compensate and can start looking for suitable methods.

Unless you are prepared to jettison hard ballast and buoyant material (beware MARPOL) you need to find a mechanism which can change volume sufficiently to give the required compensation, while being essentially incompressible. One interesting approach might be the change of volume as wax melts or freezes. There's a theory that this is how deep diving whales regulate their buoyancy and much better evidence that some copepods do the same. It's the effect that operates the thermostat in automotive cooling systems. I wonder if you could install large wax-stats fore and aft, each with an embedded heating coil. When you are ready to launch, melt the wax in both pots, add solid ballast to achieve neutral buoyancy and trim before turning the heaters off to let the boat sink. Googling, I see that there's already been a small scale demonstration of this principle.

Sounds like an interesting project.

A.

RE: Submersible ROV

(OP)
Sorry i meant to make it more clear. This would, in essence, be a traditional sub. It would have a standard ballast hull (outer hull) and have a inner hull that would make up the ballast cavity. Definitely not attempting to use the entire hull for ballast. It must be a sealed compartment unless i'm way off. My only point to the cubic feet of 5000psi air (i think where it may sound like i was implying a ballast hull) was that i don't think i would have sufficient make up air within the main hull to make up the 5000 psi (through a compressor for instance). Also this is totally unmanned. It's completely remote or on-board guidance.

Here's one theoretical layout. Me throwing 3 out there in the op didn't help.

-A cylinder shaped hull with hemispherical ends.

-A ballast tank connected to hull.

-Air cylinder of holding air. Makeup around 500psi. (purely makeup volume for compressor into high pressure tanks)

-Compressor

-Air booster (6000~psi)

-Air cylinder(s)? of high pressure air for purge into ballast. (6000~psi)

Just to clarify i'm working with an object 4 feet in diameter and 12 ft long.

My craft is going to have a top fin almost like a fixed wing. Solar cells are going to occupy the upper wing surface for charging purposes. Or the other idea was the detachable platform, that could also serve as a stabilizer, in fixed position.

RE: Submersible ROV

Most deep diving submersibles tend to use incompressible materials for buoyancy like kerosene, oil, or wax. The use of air is kept to a minimum because of the compressibility and volume change issues.
B.E.

You are judged not by what you know, but by what you can do.

RE: Submersible ROV

So, 1/4" coax weighs 0.045 lb/ft. 2 miles of that comes to 475 lb. But, it's unlikely that the cable can support its own weight, so you'll need some sort of cable, which does add more weight. Then, there's the issue of getting the antenna to the surface, which will require something that can lift all the weight from the sub. Then you need a big enough winch to wind it all back up when you're done. And, since it's unlikely that you'd want to spool that inside the sub, everything has to work at 5000 psi in extremely cold water. The volume of the cable itself would be about 3.6 cubic feet.

There's a reason why US submarine underwater communications was done with ELF signals, and even at that, they needed to be very close to the surface.

TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Submersible ROV

Bear in mind that:

Traditional submarines don't usually go as deep as you're proposing - you need to understand why before copying their concepts.

Satcomms on a reelable buoy are a real thing (ELF data rates are never going to be fantastic). Remember that horrible, tearing, screeching sound in 'Crimson Tide'. Not saying they're troublesome, but..

There are other sorts of strong string beside Kevlar. Dyneema/Spectra is widely available and has some attractive properties.

A.

RE: Submersible ROV

(OP)
IRstuff, zeusfaber, berkshire

Thank you for your replies! Sorry had a long weekend and was just able to sit down and catch up!

You have all certainly highlighted a big issue. First and foremost i do not want to cause any issues with MARPOL whatsoever. So hard ballast would be out of the question for myself. Though it could make things much easier :P

So i appreciate all the replies, really i do, it helps me think of what iv'e not thought of or not thought enough about. First i'd like to address IRstuff's point.

IRstuff- On the comm platform. My thought was a detachable buoy or raft, like i mentioned, that would have buoyancy to sustain itself and the weight of any tether or wiring used. Otherwise the craft would never surface. To my calculations i was only going to need +25 lbs or so of buoyancy. Coax is not something you would use for transmission here. Perhaps an electrical could chime in here but i think i could get away with even a very fine wire. My thought was magnet wire. Check it out. Comes in sizes around 0.025" and even .015". When i was in manufacturing I worked with wire-edm, that stuff comes in spools of .012", .010", and as low as .0018". Though it's typically brass. The .002" stuff brakes easy as can be but you would be surprised at the strength of the .012". You would cut you hands wide open before you pull that wire apart. Anywise i digress. I thought i would use a copper version of the same stuff and boost the signal of the wire. I could weave the kevlar (or other) with the copper wire and spool it. It should be more than strong enough to hold pulling 25 lbs down. I don't think the wire would need to be insulated either. It's insulated by the salt water in the sense that 5V or what ever i'm sending up that wire will never jump over saltwater at that voltage. Iv'e not thought about that yet though. My point. The weight of the wire i believe i estimated around 15 lbs not including the kevlar.

The cold water sucks for basically all challenges i'm looking at, but in terms of that wire it should, on the positive side, at least lower the resistance over the distance. Anyone know if the pressure will have adverse effects on the wire itself? Could it just shear away at that depth?

RE: Submersible ROV

(OP)
-berkshire

I have been looking into wax for ballast and its a pretty cool concept. Just not sure if i understand it correctly.

From what i'm reading its stated that in liquid state it loses density. I'm having a really hard time finding data, but i did find a tiny bit. It was a spectrum from 55c to around 90c. It showed very, very little change but it did exist. I calculated that 12-ft3 of paraffin would drop 15 lbs based on the above mentioned spectrum. But that's a lot of wax! I'll need to do more research on that end. Its a good route no doubt, but then think of how much heat energy ill need to exert to simply melt that down.

Also i'd need to figure out if paraffin simply expands, or gains volume in liquid state, where overall density would stay the same. Or if it in-fact losses density over volume, with volume remaining constant.

If the overall density does not change... It's not very helpful in the way i'm thinking about it.

RE: Submersible ROV

?? Salt water is VERY conductive, and resistive loss over 2 miles will certainly swamp out your transmitters at 5 S/m. Without controlled impedance (insulation) you'd be lucky to get more than a few bits/second; RS232 with controlled impedance only gets about 50 bps over two miles, and that's with higher conductivity wire.

Your 12 mil wire will have a round trip resistance of about 1500 ohms.

Fiber optic cable might make more sense.

TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Submersible ROV

(OP)
IRstuff-

I had completely underestimated the conductivity of seawater. It is very conductive. It seems controlled impedance is really the only way to go on that front, which more or less eliminates sheathed wire? I would need a mighty thick wire to eliminate loss.

Could you take a look at this technology? Its an underwater modem that works via transducer (i think). They claim they can achieve distances greater than 3km.

edit*** (forgot the link :P )

http://www.dspcomm.com/products_aquacomm.html

So I have contacted that company for more details. Specifically mentioned my application would be an extreme depth communicating to a topside buoy. Currently awaiting there response.

Also I looked into fiber optic cabling. It could work. Though a lot of vendors are stating around 1000m max distance. I'll look more into this matter as it would be the absolute fastest comm and could even provide real-time motion and video. Just a thought.

My concern with the fiber optics is the pressure and max distance. Any input on those two challenges or on the modem tech? Even if that modem works at the distance needed it only moves at 480bps baud. Fiber is attractive. Its just can it withstand the pressure. I might be able to test this here in lake michigan. I'm 5 miles from the shore. Depths can be as deep as 350m in the lake.

RE: Submersible ROV

(OP)
Oh? Did you find some more information elsewhere? All i read is they have two models one at 100bps and a 480bps. They both hinted at the same range more or less.

"AquaComm is available in 100 bit/sec and 480 bit/sec versions and in two forms"

What did you think of the fiber optic cable? I'll run the numbers in a few hours when i get home on reel size and weight. They said it's only good to 1000m. But that's at 100Mbs. I don't need 100Mbs, so its possible i could get a very usable data rate at the range i'm interested in.

RE: Submersible ROV

(OP)
Also i think i'm going to adapt the concept of our older Trieste sub-marines for buoyancy. It makes too much sense. Have one large buoyancy tank filled with oil or gasoline. It gives the craft buoyancy and since the gas inside the tank is non-compressible, there are no forces to fight, and wall thickness of that tank can stay to a minimum.

One had managed to submerge to Challenger deep depths. I read that, about 5,000ft before the floor one of her windows cracked and it shook the whole sub. But it held.

(OP)

RE: Submersible ROV

I absolutely recommend you to consults experienced engineers and use high-tech underwater thrusters. The field you have selected for activity is really hard and I think you need to have some technical coach.

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