Is this possible?

[JWLaRue]

From my perspective, there is

From my perspective, there is nothing 'wrong' with wanting to build a static diver as your first r/c sub..but I would say that the further you stray from accepted principles, the more likely it is that you will have a number of potentially insurmountable problems in getting the boat to run.

For example, you mention using balsa wood. While possible, it is not generally thought to be a good idea because of the difficulty in ensuring a perfect waterproofing for the wood. Water will make it soggy and heavier. It is also very prone to (sometimes serious) damage with only minor knocking about.

The advice provided by Andy regarding your question about a sub made from sheet metal should not be taken the wrong way. This is a good example of deviating from accepted principles. This now takes you into the arena of needing to do weight vs. volume calculations (reference Archimedes) in order to determine the necessary internal volume needed to float a hull made from sheet metal. It can be done, but if you are not in a position to go through that process I'd suggest avoiding it.

So....in coming to the r/c sub hobby, it sounds like you need to determine what your goals are. What is it that you want to get out of this experience? I assume that you'd like to end up with a functioning r/c sub that you can use to patrol the local pond or pool. Do you want to learn the skills necessary to design and build your own dive module? Or go through the weight/volume calculations for hull design and materials selection? Or.....?

You stated "What knowledge about how they work do I seem to lack?"....that is not a question that any of us here can answer. Only you can provide that answer. The fact that you stated the question presupposes that you feel that you already know everything about the subject.....?

-Jeff

[Guest]

I was more concerned about

I was more concerned about the following suggestion.

yes, definitely need to keep the weight low. I'm considering not using a WTC in order to keep the weight low and for sheer simplicity's sake. I know the risk though and am not sure if I want to take the chance. I might just do what I do in my cars and balloon the equipment (aside from motors of course) to minimize the amount of water that can contact the electronics

In the submarine world, we have a magic phrase called 'Metacentric height'. It relies on two forces, buoyancy pushing up and gravity pushing down. The greater the distance between these forces, the more stable your sub is. Bit like a chopper, where keeping the weight low and the thrust high up helps maintain a stable hover.

The cylinder helps the force acting up, the radio equipment inside the tube, will help gravity acting down.

By removing the cylinder, you remove the buoyant force acting up, this will do little to improve the stability of the boat.

I've completely ignored the perils of water pressure on your balloon idea. Don't underestimate the loads placed on a model submarine. In fresh water a radio signal can extend down to about 15 feet. At this depth you have about 7.5PSI acting on your boat. Anything soft, like a balloon will compress significantly. This has two side effects, the buoyancy of your boat will decrease markedly as it dives deeper, and the thin membrane is likely to tear and leak.

Sheet metal is an excellent material to build a submarine from, provided you know what you are doing. High in tensile strength and thin, which is useful if you want a small ballast tank. However you will need to add significant buoyancy below the waterline to counter the extra weight of the material. Aluminium, the lightest practical metal to build a sub from is about three times denser than water. Compare this with GRP at about 50% denser, or most thermoplastics which are roughly the same density as water or within 10% and you can begin to understand why most model submariners employ plastics for construction.

Most woods are significantly lighter than water, but they are very difficult to seal adequately. You need to coat them liberally in a high quality resin, epoxy being the best. Even then most subs I've seen constructed from wood give their owners problems. It only takes a pinhole or two for hydrostatic pressure to force water into the wood. It may take a while, but eventually your boat will literally start to come apart at the seams.

It often takes a bit of explaining to newcomers, and indeed to some seasoned model submariners why a deck for say a Type VII made from 0.5mm brass would require a smaller ballast tank than an identical deck made from 1.0mm polystyrene, despite the former being about four times heavier in weight.

If you're serious about building your own boat from scratch, I'd recommend you purchase 'Model Submarine Technology' By Norbert Bruggen, published by Traplet. Tough read for a newcomer, but it really does cover pretty much all bases when it comes to this hobby.

Andy

[chips]

Most of us use the

Most of us use the KISS principle when it comes to model subs. Almost everything we do today has been proven to work well over the years. This is why most of use a removable WTC to house the elctronics and ballast tank - it's a simple system that works reliably. And we build mostly "wet-hull" subs, where the interior of the main hull is completly free flooding; allowing a relatively small ballast tank to adjust the boat from surface trim to submerged trim in a few seconds. There is usually a lip between the two hull sections to help align them when assembled. In a "dry-hull" boat, the interior is completly sealed from the water, and larger ballast tanks are needed to submerge the boat. We're using 4 channel radio to control the throttle, rudder, dive planes and ballast tank.

Depending on the ballast system used, a single servo: operates the vent valve at the top of the ballast tank, and a valve on the compressed gas tank; operates a reversable pump to move water into or out of the ballast tank; operates a reversable air pump to move air into or out of a bladder in the ballast tank; or operate a piston in the ballast tank. Add additional ballast tanks, and you may have to add additional servos on extra channels.

You want to explore the lake bottom with an installed camera. If you plan on using a video camera, it is probably on 2.4 GHz - which doesn't penetrate thru water very well. You'll need an extended video feed antenna up above the water surface.

Using sheet metal to build the entire hull is not really a good idea, especially if you mount the radio receiver antenna completly inside the hull. The hull will act as a Farady cage, and your receiver won't get any signal.

Relying on a balloon alone to waterproof the receiver and other electronics is not a good idea. as you can not get a completely watertight seal. By the time you notice water intrusion in or with your camera, it may be too late to surface the boat, as the rx will probably be ruined by water already.

[chuck chesney]

There are three basic states

There are three basic states of knowledge.

#1. You know what you know.

#2. You know what you don't know.

#3. You don't know what you don't know.

Watch out for number three. That's where people with many years of
real world experience, like Skip Asay, Dr. Art Broder, Mike Dory and about a dozen other folks can make all the difference between a rewarding hobby and a frustrating, expensive, and ultimately failing exercise.

I'm a rookie...I've only been running subs about twenty years, so I
hang on every piece of advice that these masters of the art post.

[mrcandyman]

Thanks for the responses guys.

So

Thanks for the responses guys.

So you guys are building wet-hull subs primarely then? It is a simpler concept than keeping the outer hull completely sealed, and sinc epressure would be equal internally to externally, the fact it's plastic woudln't really matter. I'm surprised though that the WTCs are that tight. I was assuming they were a safety precausion as well as being a pressure hull to absorb the forces acting on the outer hull. If the sub is being run wet hull though then that is not the case. It would still be a pressure hull of course but would by no means only be a fail-safe.

About the depth issue and signal quality, I had already intended to make floating antenna. The most I'd want to take the sub down to is 30 meters. I'm not sure if that depth would cause me to lose too much boyancy and sink though. How far has somebody sucessfully taken one of these subs down to?

I'll try to find the recommended book and also try to find more pictures of assembled rc subs. Thanks for the help guys.

[JWLaRue]

As a general rule-of-thumb....the wet

As a general rule-of-thumb....the wet hull design seems to be preferred here in North America, while the dry hull design has been a preference in western Europe. This overly simple generalization seems to be breaking down over the past couple of years.....not exactly sure why.

You asked:

How far has somebody sucessfully taken one of these subs down to?

Answer]http://www.subcommittee.com/forum/icon_lol.gif[/img]

But seriously, building for a design depth of 30m is not a normal design parameter for most folks. It certainly can be done with extra care taken in designing/building the various through hull or dive module penetrations. I would suggest that a working depth like this is a very good reason to use the wet hull approach with a cylindrical dive module to give maximum pressure resistance.

There have been a couple of folks who have used their subs in rock quarries and taken them down around 20m.....usually while tagging along with SCUBA gear.

-Jeff

[chuck chesney]

mrcandyman...

What kind of model

mrcandyman...

What kind of model submarine do you have in mind? When you talk about taking a sub down thirty meters, your almost talking in the realm of a submersible ROV type, rather than a model submarine.

When it's an ROV, it's in a different world than what model builders are usually talking about. The materials, mechanics and electronics get VERY expensive rather quickly. You really should have a very through working knowledge, probably on a post graduate level, of physics, material properties, hydrodynamics, electronics and fluid dynamics, as well as a chest full of money and a full machine shop if you want to build something along those lines. Otherwise, as Jeff LaRue said "it will go all the way to the bottom"...once. What is the advantage of taking a model sub (if that's what you really want) that deep? Once the submarine model is under water about three or four feet (or less), the illusion is complete...it's gone. To steal Andy's (Sub Culture) clever tag..."Why are you staring at an empty pond?"

[Guest]

In 1998 I dived a

In 1998 I dived a great little sub called the Robbe Sea wolf in lake Shasta in California to a depth of 62 ft before I lost radio signal and she surfaced,it took about 10 minutes of nail bitting for her to finaly make it to the serface.

I was on a boat with a fish finder and watched the hole thing to that depth.
The bottom was still another 20 ft dowm!Upun opening the sub there was no water.
Robbe makes some great WTCs and have kept to there standards to this day,I would not hesitate to take another one of my Robbes down again but so far I have been to around 25ft in the clear rivers here in central Florida.
This can only be done with very clean clear water with no adverse minirals as that is the limiting factor for the radio.
I have had god luck with both my own desighnes of WTCs as well as Robbes but there are several makes that dont pass the musterd!

Dave

[mrcandyman]

Simple, chuck. intend to "explore"

Simple, chuck. intend to "explore" the bottom of the water. The lakes around here mostly only go down 30 meters. Having read a bit more into ROVs, they might actually be the way to go, as you won't have communication limitations. Not sure if there's any mechanical differences, I'll have to research this.

Thanks Aquadeep! Ya, the lakes here have VERY few minerals in them. I don't expect that I would have many issues with signal quality, but that's whta fail safes are for. Still going to look into ROVs though to figure out which way to go would be most practical to me.

[noney]

Hi MrCandyman, I use to

Hi MrCandyman, I use to live in Kelowna, B.C. and I explored the bottom of several lakes in the area down to about 100 ft. I found a lot of neat stuff, mostly old bottles, but I did not use an RC sub. If exploring the bottom of the lakes is all you want to really do, then I suggest SCUBA. Control is alot easier, don't have to worry about loss of signal, bouyancy issues are much simpler, costs are probably about the same, no batteries needed, and propulsion is simple. The most important difference is failure to surface. Its a real bummer if this should happen.

In determining material for a sub here is a simple rule. Things float because they weigh less than the water they displace, and things sink because they weigh more than the water they displace. A cubic foot of water contains 7.5 gallons, and each gallon weighs 8.34lbs. This does not take into account all the stabilization issues etc. all of these knowledgable guys have been telling you about.

I'm brand new to this hobby, and I have learned more in the few weeks I have been listening to them then I can adequately describe, except that which I have learned that I don't know. Its all fun.

Gene