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What works Underwater ?

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  • LilDiLilDi Posts: 229
    edited 2009-07-09 20:27
    At 100 feet in salt water = 60 psi
    At 1000 feet in salt water = 450 psi
  • W9GFOW9GFO Posts: 4,010
    edited 2009-07-11 02:56
    LilDi said...
    At 100 feet in salt water = 60 psi
    At 1000 feet in salt water = 450 psi

    As they will tell you in dive classes, every 33 feet is one atmosphere. So 100 feet is three atmospheres. 1,000 is 30. Personally, I don't go past 7. wink.gif

    Rich H
  • Rob_WRob_W Posts: 32
    edited 2009-07-19 02:04
    Here is a link that describes a typical system currently used for underwater communications. This will help spark imagination for a method of communicating with an ROV. Piezoelectric sensors are utilized to communicate underwater. I think the expert minds here can come up with an inexpensive version of this type of system to be used with a Prop or Basic Stamp in some fashion. Any ideas are most welcome. Methods of water-proofing a cheap piezoelectric sensor would be helpful for a ROV project.

    http://www.oceantechnologysystems.com/through_water.shtml

    My interest is in using a simple ROV to search local waters for lost items like watches, spare change, jewelry, anything people tend to lose at the beach; using sensors like magnetometers to detect objects of interest. The simpler the better is what I would like to achieve. Scuba diving yields interesting items, but an ROV would be a much greater hobby to accomplish such a task. Diving is a pleasure and one can enjoy the ocean in this manner, but as you age it is not always practical physically, yet an ROV can do simple tasks for us, hence my interest in building an ROV. Video would also be a plus. A robotic arm to manipulate objects found on the ocean floor is also desired.

    The most beauty of the sea is found in the 1st atmosphere, which is readily accessible, ripe for experimentation, and you can usually swim after your project if necessary....

    Any ideas would be greatly appreciated.
    Thanks to all that reply

    Rob_W
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-23 23:42
    Thanks everyone for posting - sorry it's taken me a while·to reply.
    I'd like to propose that we ask·to have·this thread moved to the Robotics section of the·forum.· Because we are expanding the topic to the overall subject of submersibles. And that's great, just seems more appropriate over·there.·ROV's or AUV's·really are robots, they just like·to get wet!· I'd like to rename the thread to "Yellow Submarines"·once·it moves and continue with·replies to everyone's comments so far.
    What do you think?

    - Howard

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  • mctriviamctrivia Posts: 3,772
    edited 2009-07-24 06:16
    You could easily fill your ROV with potting compound. would be expensive but would not much with electronics. Deionized water works also but needs to be done in a clean room as any impurities screw things up. These methods of course would both make changing your buoyancy impossible as you need a gas chamber.

    Com speeds under water via sonic transmitters is approximately 1400m/s with excelent range. I know if you listen carefully you can here the beep on a timex watch from 50m tried it once in an olimpic size swimming pool.

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  • kwinnkwinn Posts: 8,697
    edited 2009-07-24 19:01
    My idea was more like having the motors and electronics in separate enclosures filled with a non conductive liquid such as oil and having the cables go through waterproof connections. The rest of the sub could be water filled and have bladders or sections to use for buoyancy control. Having a hull that does not need to withstand high pressures would make for a lighter less expensive unit.
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-24 20:28
    I've asked the thread be moved ... not sure if that's OK ... let's see...

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  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-07-26 00:16
    LilDi said...
    At 100 feet in salt water = 60 psi
    At 1000 feet in salt water = 450 psi


    If 100 feet in salt water = 60 psi, then why does 1000 feet in salt water NOT = 600 psi ???
  • CounterRotatingPropsCounterRotatingProps Posts: 1,132
    edited 2009-07-26 01:04
    E.Aye

    like atmospheric pressure is caused by the weight of the air on the surface of the object, similarly, water pressure is caused by the weight of the water on the object.
    We have approx 14.7 psi (or 1 atmosphere) pressing on us at sea level. Water's about 1000 times denser than air. Each cubic foot of (fresh) water weighs about 60 pounds - not sure about salt, but it's decidedly more.

    Expanding on what W9GFO mentioned earlier:

    For (about) every 33 feet down into the water we go, the pressure increases (about) one more atmosphere (atm). At ~66 feet, the pressure is ~ 2 atm (~ 44 psi), and at 99 feet, the pressure is ~ 59 psi. Saltwater is denser than fresh, so the pressure is (slightly) more in it and less in fresh.

    - H

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    Post Edited (CounterRotatingProps) : 7/26/2009 1:22:14 AM GMT
  • ElectricAyeElectricAye Posts: 4,561
    edited 2009-07-26 04:58
    CounterRotatingProps said...
    E.Aye

    like atmospheric pressure is caused by the weight of the air on the surface of the object, similarly, water pressure is caused by the weight of the water on the object.
    ...

    Yes, I understand that. But why is the build up of pressure not even close to linear (according to LilDi)?

    If each cubic foot of water weighs 60 lbs, then we're looking at 60lbs per 1728 cubic inches. (BTW I haven't checked that value for water density.)

    An object at a depth of 100 feet is at a depth of 1200 inches, therefore the water (gauge) pressure exerted upon the object would be (60lbs/(1728 cubic inches))*1200 inches = 41.7 psi. (which is about 3 atmospheres of gauge pressure, roughly speaking).

    An object at a depth of 1000 feet is at a depth of 12000 inches, therefore the water (gauge) pressure exerted upon the object would be (60lbs/(1728 cubic inches))*12000 inches = 417 psi.

    The salt content of the ocean changes a little with depth, and so does temperature, and even density due to the ever so slight compressibility of water.... but.... um.... maybe I'm wrong, but I don't think it's gonna give numbers similar to what LilDi is suggesting.

    BTW, gauge pressure is what you'd normally measure with a pressure gauge. If you tested it for absolute pressure, then you'd have to toss in an extra 14.7 psi onto the results to account for the weight of earth's atmosphere.... unless, of course, you're in a lake at high altitude, in which case there's some other math involved.


    scool.gif
  • W9GFOW9GFO Posts: 4,010
    edited 2009-07-26 17:07
    CounterRotatingProps said...
    At ~66 feet, the pressure is ~ 2 atm (~ 44 psi)

    2 atm worth of water pressure + 1 atm of... atmosphere makes for 3 atm at 66 feet.

    What LiDI should have said was;

    At 100 feet in salt water = 45 psig
    At 1000 feet in salt water = 450 psig

    @ElectricAye - Compressibility, actual density of seawater, salinity, temperature and the inverse square law as it pertains to gravitational acceleration aside. I believe you are correct in you calculations.

    Rich H
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-07-27 17:06
    Thread being moved from Sensors to Robotics by request from OP.

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    Chris Savage
    Parallax Engineering
  • lardomlardom Posts: 1,659
    edited 2010-05-27 15:38
    I read an article several years back concerning submarine sonar and the harm it does to whales and dolphins. If I remember correctly the power of· sonar pulses is·comparable in decibels to an explosion. This is just a comment. We need rovs in the Gulf of Mexico right now and we need to be able to communicate with them. This is a discussion I'd like to listen in on.

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  • MarkovMarkov Posts: 19
    edited 2010-06-21 19:07
    this is an old post but just for reference for you Jacques Cousteaus:

    US Navy subs carry a buoy on their back that they reel out from a classified depth to recieve "radio" as an 'occasional routine'. Navigation is by exceptionally accurate gyros (not only are these for navigation but also for targeting--so they know always precisely where they are--3 gyros of course --that's a nobrainer--X,Y,Z are 'calibrated' before patrol--on boomers the room housing the gyros stays locked even when submerged on patrol--off-limits to most of the crew. The gyros can be checked by satellite occasionally--a mast (periscope) is put up (above the surface) to do this--triangulation off satellites. The buoy is run just beneath the surface. there are classified limits on depth and speed (cable loading). It is a big guffaw when someone broaches the buoy--everyone on board knows -- and it makes a good bit of noise as far as submariners are concerned. There have been a few occasions where the cable found its way to the screw (something you would need to keep in mind)--generally due to operator error in the 'Navy'--like forgetting the buoy was reeled out and commencing manuevers without reeling it in first. Otherwise, it obviously can be 'cut" loose for one reason or another--say a trawler's nets or some other Smile in the water that wasn't detected. For whatever reason, when the buoy is lost, then the race is on (or used to be) between opponents interested in recovering the classified technology). So you might design yours to blow up or something if it gets loose.

    The point is if someone was building a model-- it would be entirely appropriate to design a buoy for a submersible that could be used similarly --making the problem much easier. And of course, if it is not a model--then it seems appropriate to float a reciever that would allow even easier communication or just use a wire.

    Oooga--Oooga
    "Whiskey"
  • MarkovMarkov Posts: 19
    edited 2010-06-21 19:14
    don't understand the sonar claim about whales and dolphins--submarines do not use active sonar (they don't ping). Submarines rely on passive sonar which doesn't put out--they have the ability to "oing" but it is suicide to use. It's those P-3 Orions and their sonar buoys and russian equivalents if anything but i never heard of sonar buoys driving away the whales and dolphins.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-06-21 20:48
    for under sea Comms I would contact "OTS " they make SSB Voice comms for divers . but with some tweaking they might be useable for Low speed data..

    I SCUBA dive and have made a Ton of underwater Electronic devices from Lights to cams to Dive scooters to full one way comm units for instructors . ..

    Let me sleep on your Idea for a few nights [noparse]:)[/noparse] I may have a idea ..
    Peter KG6LSE

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    "Carpe Ducktum" "seize the tape!!"
    peterthethinker.com/tesla/Venom/Venom.html
    Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
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  • allanlane5allanlane5 Posts: 3,815
    edited 2010-06-22 01:38
    Yes, submarines CAN use "active-sonar", but because it's like shouting "I'm Over Here!" they PREFER passive sonar.

    However, when you're doing anti-submarine ops, I'm sure the destroyers and frigates ARE using active sonar -- and to get a 'return' from a solid object I would guess it does take quite a lot of power into the water. Not to mention how much power extremely low RF takes from the (I think it's called) "Pave-Low" radio system.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2010-06-22 02:26
    For under sea Comms I would contact "OTS " they make SSB Voice comms for divers . but with some tweaking they might be useable for Low speed data..

    I SCUBA dive and have made a few of underwater Electronic devices from Lights to cams to Dive scooters to full one way comm units for instructors . ..

    Let me sleep on your Ideas for a few nights [noparse]:)[/noparse] I may have a idea ..

    Peter KG6LSE

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    "Carpe Ducktum" "seize the tape!!"
    peterthethinker.com/tesla/Venom/Venom.html
    Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
    LOL
  • MarkovMarkov Posts: 19
    edited 2010-06-22 13:31
    sending signals to a submersible is entirely different than divers Voice comms.

    the reference somewhere above to the large antennae size used by the Navy is basically correct but then think about the distances involved--that's pretty much the why of the size. There is another sort of antennae/system but it would do you no good and you would be assainated if you knew anything about it and there are other ways subs can 'see' where they are you don't need to know about because it is a secret and you are no more than a measly stupid bougesoise bum without a real need to know and it is entirely out of your pathetic means--as far as the depth issue goes it won't matter what you try to use or about how good are the electronics--beside being all wet, waves (such as sound and sonar) behave differently in water than in air. Whatever you use would not be reliable if you could get it to work at all due to the BENDING of the waves (sound, light, sonar, etc) due to all kinds of variations in the water--such as differences in salintiy and temperature--these 'bands' set up surfaces between them that sometimes bounce or more likely refract whatever waves try to cut through them. that's why the buoy. and that's why those skimmers and P-3 Orions have such a hard time finding subs with whatever sonar they choose to employ regardless of fhe power of the almighty ping. The sub just finds say a temperature boundary and calculates the diffraction and positions itself to remain undetected--and its not all that hard which is why the front line of the cold war was beneath the sea. Yeah--and why the big investments in ASW regardless of its practicality. It's always practical for the chump pocketing the change. And,yeah, you can't solve all the problems of the world with cheap little sensors and toy controllers.

    As far as whales and dolphins, i remain skeptical as this so called pinging just doesn't happen--that is there aren't a bunch of boats and planes constantly pinging the ocean looking for subs for obvious reasons--everyone who matters within 10,000 miles knows precisely where you are once you do--so pinging would be strictly a rare exercise deployed to find a suspected target in an immediate area--a rather rare occurence--and largely an exercise in futility for reasons stated above. During my 12 or so years of wasted away life sailing beneath the ocean--not one ping except for at the pier before deploying to ensure it works--because procedures said to do so. And the only whales around where up on the pier waving bye-bye and they looked beyond damage to Markov who remained inside the pressure hull. I've seen dolphins playing with our "Soviet" sonar buoys floating in the Straits of Juan de Fuca -- waiting for boomers coming or going into Bangor. Oops--when you deploy sonar buoys --guess what--they are usually listening passively because the submarines would know immediately where they where if they went active and the US Coast Guard would snatch them right up and (formally) the hunt would be on to trap the Russian sub that entered US waters to drop them off. So yeah during ridiculous exercises or when you want to depth charge or ASROC or nuke a sub you already know is near--a very rare occurence--the P3's drop active buoys and the frigates go active but you westerners watch too many silly movies. Besides, dolpins don't vacate the area during exercises wherein some sub is assigned to say a one-mile square and limited to less than 200 ft (and the 7th fleet of Pearl, all the ships out of Vladavostock, and all the king's horses and planes Ping-Ping-Ping along and ... they still can't find it--until they make the sub launch a flare). Humpback whales don't flee shipping until the harpoons start flying. If passive sonar works (to find vessels designed to be dead quiet in the water who will also be 'rigged for ultraquiet' if a predator is looking for them nearby) then you might imagine that your imaginings about intense energy pinging away at the marine life might be a little fantastic--.... Sound travels well in water that is--'higher energy pings' out in the water generally do not obtain better info as the problem is more likely a bending of the localized wave you are trying to bounce off an object rather than a lack of power. Further i fail to see how any credible experiment could be conducted to substantiate this. Sure there are particular circumstances i suppose. If you stuck a transmitter in the ear of a dolphin in a lab tank and gave it a mighty ping, my guess is the fish would be a little more than dizzy. Yeah and fish also get sucked into the intake of the condensers, problably get chewed up by screws, and eaten by who and whatever. And we used to carry torpedoes with nuclear warheads with a range of 2 miles that vaporize a radius of 5 miles of the ocean. DUH!!!

    the way subs were tracked is that the US Oceanographic Research Agency has a few research ships (we had the same research program on the other side) that actually laid tens or hundreds of thousands of miles of cables on the ocean floor with passive listening phones attached. The Walker spy case largely involved Walker selling us maps of the locations of these lines. Didn't do us much good so i defected and am now a rabid capitalist because i need, i need. And the NR-1 has wheels on the bottom and those just are of no use for so-called 'deep sea research' (the ocean is over 2 miles deep outside continental shelves and even the NR-1 can't get anywhere near that. but wheels would come in handy if you want to sit on the bottom of say Vladivostock harbor.)

    You would have better luck finding subs using satellites looking for heat trails in the water or better yet--magnetic fields. A sub is a big chunk of metal moving through water--well even you know the rest. Ever few years they DeGauss (spelling?) the boat at the special armature pier essentially turning the boat almost into a stator wrapping it with "CEMF" windings to minimize that one.

    I'm no Navy lifer of any stripe and not a US Navy support hoser by far but gheezzz--you wanna gripe and moan about the Navy -- find a real reason--like not enough liberty, poor pay, not enough beer to get through the day, too few coed submarine crews and no unlimited free supplies of latex accessories, and issuing swords to all the enlisted personnel--not just the officers who only are bound to hurt themselves.
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