Underwater Quadcopter

Hi

This may sound crazy.  How about a quadcopter designed for underwater use.  Brushless motors operate perfectly well submerged and the rest can be waterproofed quite easily.  Idea being that one would use small props, basically the quad would operate in a different medium but essentially it should still stabilise as it does in air.  I thought about escs (which don't like water) getting hot but they could be exposed, covered with tectyl or some other waterproofing spray.

As a fail-safe, waterquad would be slightly buoyant so in case of power loss, it would merely float to the surface.  One would then have keep throttle on all the time to stay submerged and power up to sink as opposed to normal operation.  I know that 2.4ghz does not work underwater but the older 35mhz systems do.  For fpv, 1.3ghz could be used ??  Also I wonder which flight controller would work best, kk2 maybe for cost-effectiveness. 

Has this been attempted before and if so, any success?   Couldn't seem to find anything on this concept.  I'm itching to start building but somebody please stop me if I'm wasting my time. 

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  • I started on an ROV project this weekend so this is timely. I did briefly consider acoustic wireless, the thought process being '56k modem->speaker->microphone->modem'. Very quick Google returned some results for acoustic modems but seeing the scale of the challenge opted for a wired tether.

    Something I did consider, showing some RF ignorance here, but using the 3DR telemetry radios, if one were to connect these back to back with coax (instead of putting antennas on)... How far away from a working setup would this be? Presume it would need some padding or impedence matching.

    The nice thing about the floating antenna idea is you could get a GPS on it too, because I bet that doesn't work underwater either :)

    I suppose the drawback to this is being so close to the water you are going to have a very short horizon, and maybe even occlusion from waves, before you even get into drag and paying out the cable etc

    Sorry if I'm playing catchup here but is the water/air interface the issue? What's rf proper faction like if both antenna are in the water?
    • If you mean using coax instead of transmitting through air ? then yes this would work but wouldn't that be the same thing as a tether ? and would it fly with the coax on ? If you are going to use a coax tether then there are better utilization of it than using 3DR.

      The problem with RF is not really the interface though that does present losses the problem is 

      absorption of rf in water

      after all microwave ovens rely on the efficient absorption to heat stuff. The micro waves are much higher frequency but there is a pay off higher absorption with higher frequencies and lower data rates with lower frequency. There doesn't seem to be a sweet spot that will do both at any reasonable distance under water. Low frequencies work well under water and indeed submarines use them to communicate with the land but generally the data rate is so slow the most common message sent is please contact us,, this would result in the sub surfacing (or deploying surface antennae) and using conventional sat technology. 

      Yes you can put GPS in the floating buoy and use dead reckoning to calculate where the ROV is under water but the inaccuracies are so huge it again becomes point less. I tried getting rid of the errors by using two GPS modules and one fixed in a known spot with the errors communicated to the other for correction but my simple GPS receivers don't allow me to get at the raw data and thus without spending 100's that didn't work either..

      ultra sonic s are OK for all of it bar the live video. By placing some land based TX you can calculate the position of the buoy and a similar set up underwater to get the location of the craft this can also be used to communicate simple controls. Maybe radio above water and ultra sonics under but still no video. My favorite solution is for the Quad to carry a payload consisting of a data link (possibly standard WiFi)  and fiber optic tether. I lands on the water and as it sinks the payload is left on the surface relaying the data. This would work providing you have enough weight caring capacity and battery life on the quad. Some sort of ballast tanks would be needed to keep the quad as light as possible in the air but be neutral buoyant in the water to preserve battery life. The standard quad blades work ok under water providing you stall them before they hit the water (breakage) and your motors will go slow enough as the rpm under water would be a fraction of the rpm in air...

      Electromagnetic absorption by water
      The absorption of electromagnetic radiation by water depends on the state of the water. The absorption in the gas phase occurs in three regions of th…
  • Feeling very happy by seeing this post.. i was working on this from past  4 to 5 months.. and it would be my final year engineering project if i am able to submit its synopsis and possible cost report within 15 days.. i am currently working on its design using solid works.. and i will be using  ballast tanks to maintain neutral buoyancy..water sealing is not a problem for me.. because i have to get it to a depth of 30 to 40 m... i am facing problems with propellers because i need efficient propellers for which could used for both underwater as well for flying.. is it possible ?.. i would be using 434 MHZ RF transmitter and riceiver module for under water control.. Yes i am using 2 remote controllers.. i would be using 3 motors at max 4.. and it would have flaps.. underwater camera, fog lamps, arduino , few servo's, 3  8000maH batteries.. first i thought of using sonar to get clear picture of underwater environment.. but since it is costly and i only need to be at max depth of 40 m depth at max.. i decided to drop it.. but i will be using distance measuring sensors and some sensors which would cost me less and also get the attention of my project evaluator's.. i am not a genius.. i started read about ROV and AUV  few months ago.. i don't have any practical experience.. i just read some books.. if any body could guide me to accomplish it.. i would be really happy..

    • unless I'm reading your post wrong. Two things stand out. You won't be able to use 434 mhz from a surface transmitter to a craft down at 40m you may mange a few 10 cm's but not 10's of meters. Second thing is if you are hoping to transmit live camera data over the 434 mhz then you will be very disappointed... 

      • i know many information are there in google..since i am new to this i am confused about things which i should do and things which i shouldn't.. on that i have project budget.. for which i have get best things at less price.. if you could help me it would be really helpful.. because i don't any Proff. from my college who has a knowledge of these things.. they are purely thermal and material based people...

        • 30m ? That's a lot better than I managed. If you design an antennae that floats on top of the water and thus gets rid of the water/air interface you will get a better range. If someone you know could help to build specialist antennae then maybe you'd get even more. But unless you get really accurate directional RF set up(which would be a bitch to keep aligned in the water) I really can't see you doing 40m or even 30m. However, I am certainly no expert and will be only too pleased if you manage. The other thing of course is salt water or fresh, these will act differently for an RF link. Ultra sonic  is a good reliable communications link underwater but again is very slow on the bit rate. Have a look at this link 

          data rates for video

          8kbps quoted in the paper you linked to would not get you live video with any sort of reasonable frame rate. But maybe one picture every few minutes may be enough for you 

          I'm sounding negative I know. Mainly due to me spending a lot of time trying to do exactly the thing you are trying, I had some very good advice of people that know and we couldn't crack it. 

          I did have a bit of luck using lasers (in very clear fresh water) . I managed to transmit data over 30m through water using a blue laser. Again alignment is the problem with light communications. 

          If you haven't got expert advice for this at your uni then you will be struggling. You can pay big money and buy ultra sonic equipment or spent a good bit of time developing things yourself. However If you manage to transmit live video and control signals reliably over 40m of water to/from a moving object then you'd be well on your way to a Phd and that's forgetting about the rest of the project. 

          Another few ideas I had was a capacitive communicator and that is a plate on the bottom of the water and a large floating plate on the surface and fluctuate the field between them, I didn't have the skill or kit to make this work either :(

          if your craft is always on the bottom or always follows a certain path then a leaky feeder on the bottom of the water body within 5- 10 cm of the craft can work and you can use standard WI-fi kit...thus WiFi in the air and WiFi over leaky feeder in the water. with a programmed method of getting the ROV down to the leaky feeder once it's lost coms with the surface.

          So in short , whilst I am willing to help I can only tell you what doesn't work as that's all I managed to prove :)

          Fiber optic link was the best I came up with in the end...

          find a solution to the communications thing and you'll be a hero...

          • Has anyone considered using a towed line similar to submarines?  What about a small pod that once the drone is submerged and main rotors are shut down, the pod deploys to the surface and is used as a long wire antenna.  Once you are ready to surface the line is cut and the drone surfaces and like I mentioned earlier, could then lift off and fly back to launch site.  Could you use thin wire say 30 AWG to be used to couple receiver inside drone to a floating antenna?

      • and i just got it confirmed that i have reach max of 30 m depth.. 

      • i got it from this journal (which i have attached to this post) .. if its not possible then which wireless communication system i can use? 

        ROV TR.pdf

        https://storage.ning.com/topology/rest/1.0/file/get/3702712958?profile=original
  • I've been getting my ideas together on this project. I'm guessing there isn't much enthusiasm for it on this forum unless it's a slow burner :)  I can like anyone else find out nearly all I need to know from Google searches but I also know (as I'm a established builder / tinkerer) reading information on Google can and normally is a world away from doing it. 

    In one of my early discussions I wanted to find a donor craft that was good at hovering as this would be one of the most important things on my craft. It dawned on me that as I'm in water then unless there is a current then hovering is going to be a lot easier than it is in air. I can design the craft for static stability without fast and accurate PID/electronics.   However I have never fiddled with RC craft other than flying other peoples craft and thus there is a lot of info I guess people on here take for granted but could save me days of research and error. 

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