I have been bitten by the sub bug again.
This time I am retired and have the time.
I am sure this has already been tried.
I would like to control depth with a Blood Pressure Monitor cuff and pump. Simple, good volume, small volume changes are easy. It is easily adapted to level control also.


Why did it fail ?

I am trying to think of what you mean... but having little problems. Do you mean as boyancy or as ballast? (I will assume ballast, because as boyancy you would have a one way trip...)

In water, the pump would pump water into the bag, since it can't draw air while under water...

It will fill the bag until it runs out of room, then either the bag gives (stretches) or the water stops going in. If the bag stretches then it might work, if not, it probably won't.

Assuming it doesn't stretch: Once you go to deflate it, under water, the bag won't empty; inside and outside are water at the same pressure (since you can't compress water). With this system it would only let you go deeper, but not surface.

Assuming it does stretch: If the bag itself stretched, it would force that extra water out until it is no longer stretched. To make it work with this system you would need to make the boat boyant with the bag filled to the point before it stretches, then to submerge you add extra water, to surface you let that extra go.

It will function as a fishes swim bladder. It is partialy filled with air at neutral. To dive deflate it at any rate from slow to as guick as 3 seconds.
It would only need a open ended vertical cylinder with the cuff at the top.

NO WATER ever enters the cuff or pump. Strictly air bellows action action moving water out the bottom.

Hi Cyclops:

There's loads of info on the bladder system available for you and it is a popular way to control a sub. A Google search will come up with some good links if you look for "RCABS" which stands for Recirculating Compressed Air Ballast System .. which was developed by Dr. Art Broder.

There are many pictures & articles on the following sites and each has a search function to make things easier for you:

http://www.subpirates.com/

http://www.rcgroups.com/forums/forumdisplay.php?f=60

http://www.subcommittee.com/

Hopefully, you'll find this info helpful. Each site has their "resident experts" and assistance is readliy given.

Regards,
Lee Smith

Thanks Lee. A working sub is easier than falling off of a floating log.

So, used as boyancy, i know you can easily deflate it, dive at any speed... but how do you get more air while under water? I must be missing something.

I was thinking the cuff is inflated completly with the sub surfaced.
Controlled openings of the cuff to deflate would cause the water pressure and air pressure to reduce the cuff air pressure and displacement into the low pressure WTC of the pump compartment. Yes it is very emperical, but it has brutal simplicity.

You do not ever lose your air volume. You are moving air volume and pressure in the vertical tube in the hull. THAT is what causes the sub to change displacement.

I have not tried it yet, but, why would it not change displacement in the vertical tube ?

More thought. Why can't the pump be in the top of the tube and make the operation more failsafe ?

It seems it can work either way. Just preference.

Oo. I think it just dawned on me how you are describing it. The pump and such are in a WTC, separate fromt he cuff. The cuff is in a ballast tank (doesn't even need to be sealed... or a tank, just contained in the sub), when the cuff inflates the water is forced out, when it deflates, water makes its way in.

As long as there is enough air to inflate the cuff from the WTC, yes i see it working.

I was mainly having issues with displacement vs air volume... Displacement is what will bring the sub to the surface, not the volume of air in it.

I think you have my thought on transfer of the air pocket back and forth. But I am not normal in my engineering projects and solutions.

Do we have a simplistic approach to a difficult problem ? Worth a try ?


Thank you for reading me correctly.
Rich.

It sounds like a fine idea. The release valve is easy to rig up, im sure the pump is simple too... And it can't be very expensive compared to other systems of pumps and such. Too bad the whirly birds eat up so much money... i'd love to try a sub like that.

I will check with my Omron Mfg. and see if I can get them to spec. out the operation so we do it the easy and right way the first time.

I will keep posting on results.