Hello and a question - Compressed air

[iluvsubs]

Hello every one this is a very informative site and there seems to be a good group of people in here.

I have never worked at all with RC and do not fully understand its limitations i.e. servo strength, distance (depth) from controller and things like that.

I have a lot of experience working with compressed gas and I also am an ad vide Diver. The Idea of making a RC Sub has been in the back of my mind for the past 10 year and a buddy and I have decided to embark on this project.

Now the engine we have work out is gas turbine driven using CO2 regulated at 80 PSI the speed of the turbine is controlled by gas flow (how much torque can a Servo produce to open and close a valve)

Any Ideas about a CO2 ballast system

Nice meeting you all

Peter

[koeze]

Servo's can be used to

Servo's can be used to operate just about anything. They can be bought in an enourmous range of torques and travel angles. That should be the least of your problem. About your propulsion system. This sounds very nice, operating a turbine to drive the propellor. The thing is however that in order to float under water you need a constant weight of the submarine. Driving a turbine with co2 means that your sub will constantly loose weight and thus gain bouyancy. I suggest an electrical propulsion system.
Compressed air can be used for ballast blowing (and is with great results). Another great disadvantage is he volume needed for the CO2 tanks. Also when you are out of air you're going nowhere. Whit an electric engine you can switch to a backup battery for emergency backup of power.
Last disadvantage I can think of is that the expansion of gas absorbes heat from the surroundings, in effect cooling the interior of your submarine. This in turn can cause condensation. I can assure you that all the very fine electronics involved with model subs do not like moisture.

Try googling the net for sites from sub builders and see how they tackle things.

If this is you first attempt in RC modelling and especially in model submarining I recommend starting with a kit (Robbe U47 or U2540?) Robbe homepage offer great boats that can be expanded to your liking.

Just my two cents worth

EJK

[iluvsubs]

You have brought up some

You have brought up some very good point and they are things this I will have to compensate for. The loss of weight can be overcome by having a ballast system large enough and chambered (to prevent instability from water movement)

The CO2 tank could be sealed from the electronics. sub length is going to be 10' - 15' we would be using a 5lb CO2 tank with evaporator and regulator.

How many RPM should the prop turn at?

What is the best way to control water intake into the ballast tanks?
If you think my ideas are crazy that is fine I need people to challenge them and point out flaws or things I may not have thought of. This is going to be a large scale sub if it work then I'll miniaturize it if it never comes back up I'll by a kit LOL

Peter

[koeze]

At that size I cannot

[color=#000000]At that size I cannot tell you how fast the prop should be spinning. Basic rule is ]

[silent hunter]

Hi there. Just a quick

Hi there. Just a quick comment in regards to running on gas propulsion. An example is a scuba tank. when it is filled to capacity it will sink. When empty it will float. Thus, the gas, (in this case compressed air), which is acually lighter than Carbon Dioxide has a certain density. Your sub, to operate properly will have to have pretty much the same bouyancy (or density) all the time. I say pretty much, because even water temperature will have a small but significant effect on your boat's bouyancy. The use of gas for propulsion sounds cool, and exotic. You will find though that it is not the right stuff for getting around the pond, as your boat would be continously getting lighter and lighter. Not so good for a submarine.

[scott t]

You would probably know where

You would probably know where your sub just passed by the trail of bubbles you would leave. The escaping gas might also cause gas pockets if not vented directly out of the hull.

I was at the USS Batfish a week ago, and they had a torpedo with panels removed. The openings revealed what looked like a turbine geared to the props for propulsion.

Scott

[ramius-ii]

Hi Peter]http://www.subcommittee.com/forum/icon_smile.gif
I do

Hi Peter]http://www.subcommittee.com/forum/icon_smile.gif[/img]
I do not see any practical way to get around some form of electric power as part of the drive system. One idea for you is to use a 12 volt automobile tire inflator to recover part of the CO2 and "re-compress" it for use again.

Ed

[koeze]

That would give you the

That would give you the 7.5 bar or something in that area at very low efficiency. I don't think a car tire inflator would be much help. One could think of using more than one stage of turbines each with a lower working pressure so that the (still compressed but slightly expanded co2 that exits one turbine could feed the next. This is done in steam turbines (high pressure turbine feeds medium pressure turbine which in turn feeds the low pressure turbine.) This way a large amount of energy can be extracted from the gas.

EJK

[anonymous]

As a general rule the

As a general rule the larger the screw the slower the RPM needs to be to generate significant propulsion. Speed isn't always best it can make trimming the sub very hard

[wingtip]

nitrogen would be a good

nitrogen would be a good candidate for the supply, its less likely to change density due to pressure and temp changes... this is what i plan on using in my ballast system.. Maybe it will work maybe not, thats half the fun in finding out...