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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ah yes good point unless you step up to high voltages ect but that adds another level of complexity. With the craft being near neutral buoyancy the batteries can be in the craft with no real loss to anything.. maybe a small one in the float to run the coms and then keep the tether to fiber optic...

The same type of motor will work underwater but it will require a different prop to run at the same rpm.  Something that can fly and swim using the same motor/prop combination is not possible by the laws of physics.

I agree , that's  why you don't turn them at the same RPM. You need a brush less outboard that is capable of slow speeds, Many can't but some can...

The way a motor is wound determines it's characteristics.  You can't have a motor thats good at both and has the weight ratio to be able to fly.

The only way to do it would be with some kind of gearing or swappable props.  I think this would be too much complexity and extra weight on a small craft. (And also certainly much harder than one specialised vehicle carrying another specialised vehicle)

The premise at face value is ok but its a bit like saying why can't we have an apple that is also an orange? Even if you could cross them, you end up with something that is neither.  It simply can't be both.

Ok, now I'm day dreaming but wouldn't it be awesome to make one of these a hybrid?  Deepfly Dragon using ducted fans?

This is true, however the power requirements underwater and in the air are very different. With a quadcopter-sized propeller, you'd only need a few watts of power to maneuver underwater.

An ROV is on the wishlist for BoxBotix (along with a BBBoat and BBDroid so it's a long list).  I am not an ROV expert so do not know how hard it will be.  Have some friends who do this stuff.  Will let you know if anything comes of it.

I was picturing a quad like structure with four motors on the back in a vertical "+" config.  Then *in theory* you just rotate the current APMCopter code 90 degrees in pitch.  Probably so many things wrong with that assumption, but that's why we have open source.

Wow that would be something but $1.5 million just for the water version I think it may be slightly out of my play list bracket.. :)

A word of warning to anyone that reads this and thinks model ducted fans would be ideal for a ROV. The ducted fans you get in model aircraft are only built for thrust in one direction. You reveres the fan (and thus the thrust) and the darn things come apart....obviously I'm not sure if this is the case for all set ups but I believe it is the norm...

Do you mean a standard type quad setup with the X and then rotating the pitch of the props or rotating the motor prop assembly ?

IF you had a motor with the right torque and efficiency peak to run that slowly, but you don't. It will stall and burn out your ESC.

rotate the entire frame (+ or X ; not sure which works best; if any) 90 deg in pitch.  then rotate the code frame of reference to match.  bill p helped me do something similar with VTOL code on the UAV dev board a long time ago.  let us use it in a tail sitter VTOL where the code was just tricked into thinking it was hovering a 3D plane in hover mode.  it's all a gross simplification, but i stopped doing calculus as soon as school was over. so I tend to stick with Barbarian Hacking. 

anyway, you just use differential thrust from the four motors to move around.  but you do not have depth control without at least a bit of fwd or reverse motion.  e.g. top motor in fwd and bottom motor in reverse gets you nose down.  i am sure the ROV experts will say there are many things wrong with the idea.  then we go from there.

BTW, I do not think we would use the same kinds of motors/props as a quad.  We are trying to get BoxBotix to the point where you just use the same BrainBox and different modules to convert between robots.  As noted in previous posts I think motors/props similar to what they use on OpenROV could work.

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