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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Great video, I will reiterate though getting live video stream from that camera will be impossible over radio link once you are more than a jiffy under the surface and if the controls are on 2.4ghz then they will not be far behind...

Shall I start a new thread ? or is it ok to add to this one and ask my own questions ?

My thoughts are the control system underwater needs to be a lot slower so any PID controller would have different parameters so the thing slowly rights it self.

The Air props would put too much load on to the motors ? Wouldn't they ?

Can anyone suggest a DIY type set up ? If I make one (which I'm hoping to). Can the folks on here suggest a motor and controller set up  etc? The motors ideally would be ok to run in fresh water without any special waterproofing... Hovering would be the most important thing for me to get close up stable video. I'm even thinking that maybe tilt switches would be sufficient to tell it when it is upright or not.  I'm going to admit my ignorance here and ask.. Does the quad have to tip when moving forward/backwards or side to side or can t it do it whilst being level ?

would something like the turnigy SK450 be a good donor craft ? It appears to have all the bits I'd need.  I'm conscious of the fact that I'll probably drown this thing so I don't want to spend too much until I've got the ideas sorted.  Can I get something like the SK450 without the radio gear and save some cash? ... Also has anyone got any hints how I could interface the radio inputs to a raspberry PI so I can control it over a network ...

these look perfect if you can speed control them which I guess you can however at $138 per motor they are going to be way out of my budget for four of them on my test craft... thanks for the link...

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. 

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


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

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...

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