Waterproof Quadrocopter

[dunk]

saw this little piece of awesome on DIY drones:

The Waterproof Quadrocopter

dunk.

[madsci1016]

Until i see an external video of it, i don't believe it.

If you watch closely, you see a shadow of it on the ground for a split second, and you can tell the camera is mounted on a extension away from the copter itself, so the consensus on DIYDrones is it just sticks the camera on the water and hovers above the surface.

Sure, I will admit is is possible to do, but it would be a feat. If i did it, the first video i posted of it would be from an external camera as it transitions.

And there's the whole RF doesn't not travel well in water, at most a few inches for low power RF like all hobby controllers.

[Hertz32]

hmm cool if i saw it 
but seeing is beliving as thay say

[Razor Concepts]

I would imagine the quad is on floats, and the camera is the only thing in the water. High RPM brushless motors will not spin well in water.

[Xyver]

There's no water disturbance.... If there were blades running under water there would be water disturbance... 

still cool.  I love helicopters...  and all their relations.

[Admin]

I agree with the other posters, but still, looks fun to fly!

[dunk]

yea, the whole thing is almost definitely not under water. it will just be sitting on floats with the camera under.
still awesome though.

dunk.

[corrado33]

This is somewhat related... Has anyone ever built a robot that can traverse on land AND underwater?  Cause that'd be cool.

[madsci1016]

The Navy has.

[dellagd]

Is there anything the Navy/Army/Airforce/Marines hasn't made? (imagine what they have that they don't go public with!)

[amando96]

At the 6 second mark, you can see some disturbance, that continues for about 4 seconds. at least it looks like disturbance...
if it's real,  nicely done.

[TrickyNekro]

I agree with you guys, but it's not impossible...
Brushless can run underwater... for sure....
They don't have any exposed electrical parts....
And as soon as not much salt and other stuff stay in the bearings... what's the problem???

[Razor Concepts]

I agree with you guys, but it's not impossible...
Brushless can run underwater... for sure....
They don't have any exposed electrical parts....
And as soon as not much salt and other stuff stay in the bearings... what's the problem???

The motors don't have enough torque to spin a 10 inch propellor underwater.

[SmAsH]

The resistance from the water would make them just stall and die.

[dellagd]

exactly
brushless motors are designed for air operation
listen, air is ~780 times less dense than water
imagine trying to push a 1ft square plate through air, then through water. Huge difference
they put brussless motors on model planes because the torque of the motor really makes no difference because of the density of air is sooo low. the point if brushless is high RPM

Conclusion: if the blades are 10in, no chance

I may be wrong but this is just taken from my experiences with brushlesses

[madsci1016]

Don't generalize all brushless motors. I work with underwater robots that use brushless motors as the main drive. They can be designed for underwater applications as well.

But yes, those brushless motors in hobby stores are designed for air.

[Admin]

Both the magnets and the motor coil generally have iron, and they rust like a mother . . . they'll run fine underwater - until they rust up.

[madsci1016]

Both the magnets and the motor coil generally have iron, and they rust like a mother . . . they'll run fine underwater - until they rust up.

Unless they are potted. It works fine, over 5 years running in salt water and never had any issues.

Also, most aquarium impeller pumps are brushless motors with the magnet exposed to the water.

[Admin]

Yea, depends on the materials used for the motor. But a motor not designed for water, I wouldn't make any bets on longevity . . .

[dunk]

Yea, depends on the materials used for the motor. But a motor not designed for water, I wouldn't make any bets on longevity . . .

i would have agreed with you until i saw this the other day (bottom picture): http://www.btinternet.com/~antony.gilbert/photo_gallery/photo_gallery.htm
"""47 hours of sea water and countless dives before failing"""
that's just a standard hobby brushless motor. (i have a few of the same motor from this range of motors unless i'm mistaken: http://www.giantcod.co.uk/a22088-2600kv-outrunner-brushless-motor-p-402533.html)

so using the same motor and prop combo under water as in air would greatly increase the current flow in the motor in water as the motor approached stall speed.
this would cause excessive heat build-up in the motor which would fry the motor under normal running conditions in air but the motor would essentially be water cooled....
i am confident you could find a motor/prop combination that would turn under water enough to slowly move a bot and still provide enough lift to get airborne once out of the water.
it wouldn't be efficient in either medium but it might just work.

the remaining challenge is the motor controller (ESC).
first of all the ESC would need to be way over specified to handle the increased current in the motor windings.
secondly the timing of the pulses would be completely different (ie. much slower) while in the water. you would need to build your own ESC that could adapt to the resistance on the motor shaft.

hey, i'm not suggesting anyone actually tries this little bag of crazy but i think the motors could be made to run.


dunk.

[Admin]

"""47 hours of sea water and countless dives before failing"""

But . . . 47 hours is just two days. Sounds like a function of rust over time to me!

I've worked on my robot fishes for years . . . 47 hours till failure would drive me crazy!

[dunk]

I've worked on my robot fishes for years . . . 47 hours till failure would drive me crazy!

haha. dude, flying robot.
there is no way you won't have crashed it long before you log 47 hours....

but i was more just illustrating it is possible to run these motors under water.
the motors are brushless so there nothing to stop you from applying paint to stop corrosion.
i will admit the motor life cycle will always be fairly short if you use standard $10 hobby motors but there is nothing to stop you building your own with properly sealed windings and magnets.


dunk.

[TrickyNekro]

Well... seems I have started a conversation and I'm nowhere to be found...

Well... I fully agree on dunk with this. Since coils are (actually MUST be in any kind of operation) insulated...
Then no electronics are exposed brushless can run under water...
And magnets can be covered with something that isn't fat enough to hinder their performance then....
Also you can as well use stainless steel and some heavy duty oil.... that's all!!!!

About the rotation speed... and engine burning out and.... well.... It's like wow I freaked out a little... 
Water and even more salt water is much much denser that air....
That means that... (pay a little attention here )


The trust produced by a single blade revolution is proportional to the density of the medium....


Why??? Because of the third Law of Newton.... and some more other things....

The blade doesn't need to revolve fast to produce thrust....
You don't even have to modify the blade... Although I don't claim it would be as efficient in water...

Thrust is the amount of the sum of the forces applied on a "object" over some time...

dJ = Fdt where F can be what ever force you like... And in systems that don't go at the speed of light F = F(t) isn't possible... And that's why thrust is a better definition than force, but force is more versatile in common use.

Well... where was I?
Ok... with water being heavier the force needed to propel it backwards is larger, so the force thrusting the vehicle forward is also greater!!! So the motor can run slower and but being producing the same thrust as in the air medium (well almost the same as I said there a lot of factors that determine efficiency).

Now about the thermal run down...
Well.... water's thermal capacity is much greater than air's.... But.... There is actually, Fourier's Law that must be taken into consideration, before saying that is way better....
Of course it's better... But then again there are even more many factors that must be taken into consideration...

Fourier's Law refers to, how quickly the heat transfers through a medium... But water is liquid and I don't recall is it's for solid objects only or if there are variants....

About the ESC.... well.... it's kinda easy to thing about it.... really... The frequency of the motor is the same with the frequency of the current driving the motor... But then again...
You need vector control! Not these china made ESCs....

So... Running brushless underwater is way possible... But, you can have a system running 47 hours and a system running 2 years... your choice.... :-/

Best Regards, Lefteris
Greece

[SmAsH]

And here i am wishing i understood physics =| I do agree with you tricky but im not convinced until i see a video of it from an outside view doing the stuff it claims to do. Sure, that IS possible but that video doesn't prove the quadrocopter is doing it.

[TrickyNekro]

Darn you nugget....

toy aircraft motor under water