Topic: Suggestions for a diving system (Read 12978 times)

PICKETBOAT · « **on:** February 22, 2015, 10:08:26 am »

Hi all

I am venturing into functioning submarines for the first time and have avidly read and looked at books and on line blogs regarding diving systems.

The sub I am building is only small but I would like it to be a static dive model. The WTC (a perspex tube 300mm by 60mm ID) has cast resin end bungs and I plan to fit an internal removable perspex tray to carry certain components. The power supply will be 6V and the model runs on one shaft.

Can any one suggest a diving system that is:-

Small and compact
Does not need gas cannisters
Is simple (less to go wrong)

The finished model only has nominal surface buoyancy so I am hoping it will not need an immense force to get it to dive.

The model also has functioning forward and aft diving planes and I am considering fitting an electronic stability unit to help level running when submerged.

If anyone has suggestions I would love to hear them.

Thanks

Netleyned · « **Reply #1 on:** February 22, 2015, 03:44:15 pm »

Hi Picketboat,
You might get a better response if you named the model as
someone on here has probably been there done that and would
Dive in and help (pun intended).

Ned

U-33 · « **Reply #2 on:** February 22, 2015, 04:34:57 pm »

As Ned says, we need more information to go on...is the boat a kit? Scratch built? Size?

Rich

Subculture · « **Reply #3 on:** February 22, 2015, 04:42:31 pm »

Do you want the ability to static dive the sub, or will retaining a bit of positive buoyancy be adequate.

Also does the boat have to be able to empty the tank whilst submerged? or would it be acceptable to empty the tank with a snorkel just above the surface.

This dictates whether you go for an aspirated tank or closed cycle. Pros and cons with each.

Also do you have a lathe- that opens up options.

PICKETBOAT · « **Reply #4 on:** February 22, 2015, 04:57:16 pm »

Ned

Thanks for your response.

You might be right, but I have searched about and I have not seen any other working models of what I'm building. Plenty of WW11 U boats though.

She is a Royal Navy C class sub of 1906 (first batch) in particular C1. I'm building her at 1/48th scale, so the whole model is only 3ft long and 4inch beam.

The hull is coming along well (it splits clam shell style) and I'm starting to get some of the internal gear together, motor, servos, RC gear, batteries along with a selection of possible pumps and ballast chambers. I'm currently at "the arranging stuff on the bench to see what will fit where" stage.

The perspex 60mm dia tube has been bought for the WTC and I have produced two cast resin end bungs with O rings recessed in, the aft bung is cast to accept the motor negating the need for motor mounts.

Any suggestions will add to my limited knowledge of the subject.

PICKETBOAT · « **Reply #5 on:** February 22, 2015, 05:33:31 pm »

Hi All

Thanks for the additional replies.
In answer to the questions.

This is a home built scratch model not a kit.
It would probably work as a dynamic dive model but I would like to have a go at static dive if I can make it work. The scale hydroplanes are not huge so I'm not sure if they would be effective enough to push the model under without the addition of some sort of ballast tank.
I'm not sure about the different types of dive systems. I suppose a snorkel might make it simpler. With a small model I don't propose to go too deep so I would keep near the surface.

How does a closed system work?

So many questions.

Subculture · « **Reply #6 on:** February 22, 2015, 06:13:08 pm »

Generally most model submariners trim their boats so that they are still positively buoyant, but by just a few grams. Then you only need a whiff of throttle to take it under.

Getting a boat to hover is something some modellers aim for. Waste of time IMO, and quite difficult, because the boat only has to be either side of neutral buoyancy by a gram or two and the boat will either slowly sink or rise. Much easier to trim the boat to close to slightly positive then maintain depth using the hydroplanes.

Dynamic divers without ballast systems generally have higher positive buoyancy and hence require fairly high speed to stay submerged.

A vented ballast system which will use a snort mast has the advantage that the ballast tank can be kept fairly small and you have no exposed water surface to interfere with stability.

They're also simple and cheap to make, and won't pressurize your wtc.

The disadvantage is that you can't empty your tank whilst underwater to produce a large amount of up thrust, so if you sail in unfriendly waters this system poses a bit more of a risk of losing your boat.

Closed cycle systems compress the air inside the boat as the ballast tank fills. There are different ways of doing this, some systems compress the air solely within the ballast tank. These operate at higher pressures than systems which use the entire volume of the WTC, and you also need a fairly large ballast tank. They also maintain an exposed water surface, so you need to baffle the tank usually to avoid sloshing upsetting the boats stability.

Systems like piston tanks, bag based systems etc. tend to compress the sir inside the whole WTC. these generally operate at fairly low pressures, and don't have sloshing issues. However piston tanks generally involve either an expensive commercial tank or a DIY approach, which requires the use of a lathe.

A bag based system can work well, but you have to search for a suitable size bag.

essex2visuvesi · « **Reply #7 on:** February 22, 2015, 07:57:51 pm »

Norbert Bruggen does a Dive system for the Revell 1/72 sub which a tad bigger but the theory would be the same
He uses the rubber bag and peristaltic pump method
http://www.modelluboot.de/KITS/VII/VIIc.html

Also his book is pretty much considered essential reading for sub builders.
It's heavy going but well worth perservering
http://www.amazon.co.uk/MODEL-SUBMARINE-TECHNOLOGY/dp/1900371324/ref=pd_sim_sbs_b_1?ie=UTF8&refRID=19DHJC9FWXAYXQ6NHHEA

Subculture · « **Reply #8 on:** February 22, 2015, 08:39:31 pm »

You can get much better value if you purchase the parts individually to be fair.

Basically it's a flexible bag system. Peristaltic pumps can be a bit slow, unless they're larger models, a geared pump works well and is cheap, but you will need a pinch valve to stop backflow messing up your trim.

Balloons work well as flexible bags, I used two, one inside the other and it worked very effectively, I do have some concerns as to longevity. A good alternative is saline drip bags and equivalent, assuming you have a source for them, but they're very strong and used a lot by French modellers, where they tend to refer to it as 'le baxter' system after the manufacturer of the iv bags!

Norbert Bruggen demonstrates a way to make you own custom bag from rubber sheet, with the joints bonded together. the system is used in his Delta kit.

The book mentioned is very good, although very maths intensive which gets a lot of modellers running for the hills. If you can get past that, it's extremely informative, especially for the mechanical aspects of model submarine design.

PICKETBOAT · « **Reply #9 on:** February 22, 2015, 09:00:43 pm »

Thanks chaps

This is all very informative and confirming quite a lot of what I already figured out. Although I have not "done" a sub before I have a pretty good mechanical mind and had a few ideas how I can get the thing to function. I will now go away and "mock up" how the WTC will function with a ballast tank inside it.

As you have pointed out the thing will work best if the finished sub is trimmed with only a small amount of positive buoyancy.

I had considered a sealed separate ballast tank containing an inflated balloon. The pump would then force water into the ballast tank compressing the air in the sealed balloon. (I would insert a non return valve so that water is not forced back through the pump).

To surface a servo valve would open connecting the ballast tank to the "outside world" and hopefully the balloon would expand pushing out the water. Up she pops, hopefully.

If the sealed ballast tank contains only water and a partly inflated balloon (no free air) there should be little water movement to upset trim. I am not sure at the moment if the small 6v pumps I've got have enough power to compress much air within the sealed balloon.

Off to test some pumps.

Many thanks again.

Subculture · « **Reply #10 on:** February 23, 2015, 10:06:30 am »

The system you have in mind sounds like a Darnell system in reverse. That system used an air pump to pump air in and out of a bag to displace water, and the air was stored up front in an air reservoir.

The snags are, finding a suitable bag. If the bag splits you could flood your boat, and also probably a good idea to try and restrain the bag in some way so that doesn't shift about.

Davy1 · « **Reply #11 on:** February 23, 2015, 04:05:00 pm »

Hi PicketBoat,

Very nice that you have chosen a WW1 British sub. They are rare indeed!

You don't mention your budget, but if you are going to a lot of trouble with scratch built models you maybe should consider a piston tank first.

Expensive to purchase, perhaps, but if you have a lathe and some lathe skills - cheap and possible to DIY.

(You mention that you have looked at a number of sources, hope that has included the AMS Forum.)

Best of luck with your exciting project!

David

PICKETBOAT · « **Reply #12 on:** February 23, 2015, 04:20:38 pm »

Hi sub culture

Thanks for this and for confirming that the system I have in mind has at least a reasonable chance of working.

I have located two small strong clear plastic containers with screw lids. These are 50mm dia and will fit inside the 60mm ID WTC leaving a little space for wires and pipe runs alongside. I plan to fit them spaced out within the WTC, but linked to one pump so they work as one ballast tank. Each container will have a sealed air bladder pretty much filling it. The pump will hopefully push water into the containers compressing the air in the two bladders. I shall try and work it so there is no free water sloshing around in the ballast tanks with the potential for causing instability. The outlet for each ballast tank will be at the lowest point (in the container wall as they will both be mounted on their sides). If it all works, when the servo valve is opened the pressure in the two bladders will push out sufficient water as they expand (and we are only talking small amounts) giving more positive buoyancy and the model will surface. We hope!

The thing I trying to avoid is changes in air pressure within the WTC. I figure this would put too much strain on water tight seals (prop shaft and hydroplane activating rods) and on a small model even slight water ingress will send the model to the bottom.

PICKETBOAT · « **Reply #13 on:** February 23, 2015, 04:44:51 pm »

David

Thanks for the comments.

You are right there is not a huge model choice when it comes to WW1 and pre WW1 subs. Unfortunately this is the period that interests me most, so I just had to roll my sleeves up and get on with a scratch build.
Progress so far can viewed here :-

http://www.shipmodels.info/mws_forum/viewtopic.php?f=13&t=158444

Other work commitments (and the flu) have slowed the build of late.

Subculture · « **Reply #14 on:** February 23, 2015, 04:53:30 pm »

Have you considered making the boat as a dry hull. A 1/48th scale c-class won't be huge, so the extra weight shouldn't make the model difficult to transport and being spindle shaped it will work well as a pressure hull with a radial seal. Also these boats had very low freeboard, as they were basically stretched Hollands, so even a dry hull shouldn't require a huge ballast tank.

Most hull seals based on o-rings and/or simmerrings (oil seals) can withstand modest pressures of up to about 5 psi max. In practice it's unlikely you will go to more than half that with a system that pressurizes, unless the wtc volume is very small in relation to the ballast tank.

It's best to make ballast tanks as short and fat as you get them, this helps improve stability. Also try and keep it to one tank if possible.

PICKETBOAT · « **Reply #15 on:** February 23, 2015, 05:10:27 pm »

Subculture

Thanks for this. I think I am currently committed to a wet hull, but I have taken on board your comments regarding the ballast tank.
There will be a lot of small delicate detail on the GRP hull casing (mostly the top section) so I ruled out a radial seal. Pulling the thing apart would be too risky. The clam shell hull will not include the bow and stern (with the hydroplanes, prop,rudder etc) which will remain attached to the lower hull half.
I will try a single ballast tank first (central in the WTC). I can now see the issues with two linked ballast tanks. If one empties slightly quicker or does not completely clear then huge stability issues.
The ballast tanks/containers I have in the workshop are short and dumpy so should be OK.

Thanks again. This is great being able to pick other modellers brains when dealing with a project I am new to.

Subculture · « **Reply #16 on:** February 23, 2015, 05:29:08 pm »

We actually very recently had a German modelmaker who posted his complete c-class model on the Dive-in facebook page.

He used Norbert Bruggens hull kit (no longer available AFAIK), which I think was 1/32nd scale, so a bit bigger than yours, but you might find it useful to compare notes with him. He did say he needed to incorporate a trim mechanism to adjust the boat for operating wel on the surface.

Subculture · « **Reply #17 on:** February 23, 2015, 05:42:01 pm »

One other thing I'd like to add. You mentioned in your intial post that you will be using a 6 volt system.

Most small water pumps of good quality are designed with 12 volt operation in mind. Having said that you can operate them at 6 volts, but you need to bear in mind that the pumping speed will be significantly reduced. Also I think you may find it tricky to find a pump that will fit inside a 60mm cylinder.

Small diaphragm based air compressors are very easy to find, and cheap as chips. The snag with compressed air is it's not easy to trim accurately with it.

I had a look at your build thread, and your work looks very high quality. Something you could consider is seeing if a component maker would like to trade a hull in exchange for say a piston tank and ancillieries.

Davy1 · « **Reply #18 on:** February 24, 2015, 01:19:57 pm »

Hi PicketBoat,

That is a very impressive build - a lovely model.

You are absolutely right to try to keep the superstructure displacement down to minimise ballast tank size and limit top-heaviness.

I am planning to repost an article on the AMS Forum about my Holland class and its refurbishment in the next few days, which may interest you. (I adopted different design principles to you - a dry hull and a pressure tank - probably going to be a piston tank next. )The Holland was a precursor to the C, as you know. The model performs very well not unlike the original!

Many thanks for posting.

David

PICKETBOAT · « **Reply #19 on:** February 24, 2015, 02:15:50 pm »

David

This sounds interesting and I'm always willing to learn. When you get the article up and running please send me a link.

Thanks again

Davy1 · « **Reply #20 on:** February 28, 2015, 03:30:04 pm »

Hi PicketBoat,

Done and second installment will be posted next week.
I've sent you a link, as requested.

David

PICKETBOAT · « **Reply #21 on:** August 09, 2015, 06:42:52 pm »

Hi all you submariners

Thanks for all your helpful advice, all much appreciated by a "submarine virgin",

The build continues and the WTC internals are being SQEEEZED in. Not a lot of space inside a cylinder 300mm by 65mm. The eventual system I went for is (correct me if I get this wrong) a vented semi dynamic. The ballast tank pump fills the vented ballast tank, taking the model from a surface running waterline down to having just the top of the (foam filled)conning tower above water. Forward movement, with down hydroplanes, should take the model the rest of the way under water. Stability will be controlled by self levelling electronics. At least that's the plan.

For those still interested go to.

http://www.shipmodels.info/mws_forum/viewtopic.php?f=13&t=158444&start=80

I keep dipping into this forum to try and learn stuff.

Subculture · « **Reply #22 on:** August 09, 2015, 07:11:55 pm »

I'll give you heads-up on those pumps. I found running them on more than about 4-5 volts made them run too fast, and the drive gear tends to lose its key way, resulting in a dud pump. The gears are moulded from a fairly soft plastic, and I think it heats up too quickly if the pump runs dry for even a short while.

The motor has a d-shaped shaft with the driven gear having a corresponding shape, this rounds off when the plastic softens.

My advice is to run the pumps at half speed if your system voltage is 6 volts or higher, or find another method of dropping the power to the motor.

PICKETBOAT · « **Reply #23 on:** August 09, 2015, 10:07:44 pm »

Thanks subculture.

I bench tested the pump with it attached to the ballast tank, before deciding to fit it into the WTC. You are right, at 6V it shifts the water in and out pretty quick, probably a bit too quick. I will take on board what you say and see if I can find a method of stepping the 6V main power supply down to about 3V, just for the pump. I'm not much of an electrical wizard so if anyone can help with this that would be good. No room in the WTC for a separate battery. As it is I am having to dump the plastic casings for both the RC receiver and the little ESC just to save space. It's getting very crowded in there.

Another question. Where the heck do I put all the wire for the receiver aerial ? It will pass through the WTC end bung and be threaded up one of the small brass tubes which represent one of the two periscopes (making sure it is insulated from the water). This will give it a bit of altitude to gain a slightly better reception but there will still be a shed load of wire left over. It is only a small model. Suggestions?

Subculture · « **Reply #24 on:** August 09, 2015, 11:00:55 pm »

Probably the simplest way would eb to run the pump at half speed using a reversible ESC. If you have a computer radio, you could limit the range on the ESC by setting control range on the TX, so that it doesn't go full on either way.

That's the most efficient way to do it I think.

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Author Topic: Suggestions for a diving system (Read 12978 times)