Idea = Pressure compensation with scuba dive tank

[dtrip]

Hello all,

Before starting to build my conventional ROV, I am wondering about the following idea:

1. The hull is open on the bottom side, ie communicates with water.

2. Inside the hull is a scuba tank (or the tank is outside but the hose
comes inside, remember the bottom is open so waterproofing hose/cable entries
is not an issue)

3. The hull has two electromagnetic valves, operated via a controller:
one valve releases scuba air into the hull (ie "inflates" the hull to surface)
the other valve releases air from the hull into the sea (ie "deflates" the hull, to dive)

Apart from the operational depth reaching "professional" levels, another crucial
advantage is that the build will be easy and "carefree", because one need not
worry about leaks anymore.

What do you think ?

[Bubbles]

What is the material of main hull.Is it possible to expand when you send air through scuba tank?

[dtrip]

What is the material of main hull.Is it possible to expand when you send air through scuba tank?

No, the material is either stainless or PVC.
But at the bottom it is open to the water. Like a drinking glass upside down in the water.
So when you press scuba air in the hull, the water level inside drops.

[Silver dollar]

The problem with water inside a tank is that you will have waves on the water surface every time you accelerate or "brake". This can cause the ROV to get very unstable.

[Jaman42]

First I have to let you guys know that physics is not my cup of tea but wouldn't the water pressure compress the air in the hull exposing all your components to high pressure? They would be dry but it would essentially be the same as putting all your components in a vacuum sealed bag and dropping that in wouldn't it?

[dtrip]

First I have to let you guys know that physics is not my cup of tea but wouldn't the water pressure compress the air in the hull exposing all your components to high pressure? They would be dry but it would essentially be the same as putting all your components in a vacuum sealed bag and dropping that in wouldn't it?

Yes it would be very close to what you mention. But not exactly.
Because the air penetrates uniformly inside the microchips etc.
The bag would actually break components as it "suffocates" them, because of different distribution of bag material.
Dry components can withstand huge amounts of pressure without problems, like hundreds of bars. This is a fact that I know of,
perhaps a Google search will produce results, I dont have the time to do this now. In a "conventional" closed hull,
a water leak will destroy the components because of the water short-circuiting stuff, not because of the pressure itself.

[olegodo]

Yes, it would work. This is the same principal as the old dive bells and dive helmets.
The opening in the bottom could be really small also.

Weakpoints in the electronics that I know of would be cheap condensators and membrane buttons (arduino boards have this type of button) as they are pressure sensetive.

And you would want to be completely sure that your ROV will never go upside down!

[dtrip]

The problem with water inside a tank is that you will have waves on the water surface every time you accelerate or "brake". This can cause the ROV to get very unstable.

Thanks for pointing that out, I had not thought about it.

This is indeed an issue. But is an issue arising also in the tanks of road tankers (trucks) which carry liquids.
They have solved this by internal "walls" that separate the mass so that it does not move in unison when the truck breaks or accelerates.
So it should be solvable in my case (I hope!)

[dtrip]

Yes, it would work. This is the same principal as the old dive bells and dive helmets.
The opening in the bottom could be really small also.

Weakpoints in the electronics that I know of would be cheap condensators and membrane buttons (arduino boards have this type of button) as they are pressure sensetive.

And you would want to be completely sure that your ROV will never go upside down!

Indeed I used to imagine the opening like 2-3 inches, but now that you mentioned it, a "hole" the size of a coin would be better
and offer smoother dives and ascent.

Generally the shape of the hull is an issue, but I will create a different thread for this when the time comes.

The next step is to receive the Arduino and turn on and off the electromagnetic valves, via a joystick.
That should be rather straightforward I guess (Im a programmer).
As for the membrane buttons, hmmm I have already ordered the Arduino so for now I have to live with them. I ll deal with later. There are many things to do until it goes into the water anyway.

[Jaman42]

Oh I see, that's interesting