Ballasts Needed


#1

Hey Guys,

New member here and I"m researching ROV technology. So I have always been under the impression that when you are building an underwater ROV you have to have balast tanks to be able to remain neutrally boyant underwater...is this not the case with the OPEN ROV?

- Jeff


#2

Correct- OpenROV is inherently very close to neutrally buoyant in fresh water which means it won't sink down or float up if left alone. Because water has (effectively) the same density at any depth, and the amount of water the ROV takes up (it's displacement) stays the same even when under pressure, as long as the mass of the ROV is equal to the mass of the water it displaces, its buoyancy won't change. There is a propeller on the top of the ROV which thrusts it up and down to change depth, and that works great.

As a matter of practice, we also like to make it so that instead of being perfectly neutrally buoyant (so the ROV will stay at whatever depth you put it at indefinitely), we make it slightly positively buoyant, so that if we loose connection with it, it will slowly come to the surface.

Since salt water and fresh water have different densities, (and temperature can also effect water density) the fine tuning of the ROV's mass is done by adding small lead weights (actually little bits of thick solder) to the ROV.

Hope this all answers your question!

Eric


#3

I have the opposite problem. I have a version 2.4 OpenROV (KickStarter pre-built). When I did my initial bathtub buoyancy and trim test, the ROV was front-heavy and negatively buoyant (it immediately sank).

I have noted that some pads (made of some sort of foam) were added inside the thruster housing. I assume that was to add flotation.

Does anyone know the best way to add flotation and adjust front to back trim on an OpenROV.

While I don't plan to use my OpenROV at 100 meters in depth, I would think that objects like ping pong balls would crush even at 20 or 30 meters in depth (~2 to 3 atmospheres of pressure). Thanks.


#4

I have seen different Solution for Photo Equipment.

Vary Hard Foam, like some kinds of florist foam or Closed-cell Polyurethane Foams.

Also very common. ALU-Bootles.

http://www.tauchvideo.com/forum/att/2467/Cam-2.jpg

Or you use Anny kind of tube you can close at the ends. I.e. water PVC Pipes.


#5

Thanks. I think that I will try a couple of PVC water pipes.


#6

Has anyone measured or calculated the displacement of a base OpenROV?

I would think that it could be calculated fairly closely using the area of the acrylic sheets, tubes, the motors, and propellers. Then multiplying that area by the weight of water (or salt water).

or

You could measure it by measuring how much water it displaces in a measured container.


#7

I have tried ping balls, fishing floats, small inner tube, and PVC tubes. I have made several different size PVC tubes trying to fine the right size. I now have large PVC tubes 1.5 inch dia. by 11 inch. and add weights on the sides to balance it out. The rods on the bottom are an easy spot to add weights and this works pretty well. All so I can readjust for different payloads.

1377-openrovlake1.JPG (297 KB)