RCABS Pumps

[jcopter]

I Got one more question
Does anyone know/or tried to use an Aquarium Pump for a RECARBS system and if so how did you do it? I was thinking that a cheep Aquarium pump may work Anyone know
Thanks Jack

[Subculture]

You're better off using the range of pumps from here (http://www.smartproducts.com).

They're cheap too!

Andy

[jcopter]

So Hey Andy thanks
Just curious do you have a reason? I understand the Quality I just was going to try something different to see if it would work, also got a bunch of these "Free" aquarium pumps sittin around
Jack

What does RECARBS mean?

Best small DC system I know of first off is Skip Asay's SubTech pump system. Small, low battery draw, high volume of water moved for it's size. http://www.rcboats.com/submarines_only.html
Very reliable, I recommend the Propel HP blow back up too with it as a hybrid system.

Steve Reichmuth

[Subculture]

Steve,

I think he is referring to RCABS (recirculating compressed air ballast system).

By all means try out your aquarium air pumps. You may find them a little low on cfm (cubic feet per minute).

Suck and see, mock up a cheap ballast tank- you can use an old plastic pop bottle, puncture a couple of holes in one side, attach a pipe to the other and connect to the pump. Time how long it takes the pump to suck the air out of the bottle. If it's reasonable, then you have a goer.

Andy

I see now. Thanks Andy. RECABS must be a closed system? If you go that direction, it is different system than Skips design then I believe.

Skips Hybrid system needs an air source, driving the boat near the surface, broaching a mast or sail, then pumping out the water, the air source displacing the ballast water via one way Tee valve. Why I recommend the propel back up, so if you are unable to reach the surface, say a propulsion problem, fowled prop, you are still carrying a small source of propell as a back up with you regardless of depth to displace the water in your ballast tank.

Steve Reichmuth

[uboot]

Do those pumps work on DC current? I tried a windshield washer pump on my type VII, on the bench it worked fine, but I added side bladders later on and it just took too long. The pump & bladders out of the blood pressure cuffs seem the best. I tried to get the pumps from the supplier Art Broder found but they wern't interested in low vol retail.

[Subculture]

Smart products pumps work on DC, yes.

They're also happy to sell you one or a thousand.

[Bigdave]

I was told they no longer sell in low volume, and they had a price increase across the board in Jan. :shock: BD.

[Subculture]

Oh dear.

You may still be able to obtain a pump or two 'for evaluation'. ;)

Failing that, there are a couple of other alternatives.

You can purchase cheap tyre inlator compressors. These aren't the best quality units, but they do work okay for our crude application.

Only suitable for medium to large boats.

The other alternative is to hunt out some worn glowplug engines.

These can readily be converted to compressors, by replacing the glowplug with a non return valve. You will need access to machining facilities to make your valve though.

Andy

I'm amazed here after all the work Art , Dave and myself included have done with RCABS that there are still people asking what it is? In fact on other forums I've heard people put it down. Ask what do you do when the balloon pops? Or it can't work very well. We don't use balloons for one.

I have a lot more problems getting reliable use out of the propel system as valves freeze, schrader valves screw up, or you run out of gas. Not to mention 10 bucks a can!

I have demonstrated numerous times on video the operation and effectiveness of this system in very good detail. The videos are all posted here, on SC and RC Poops.

It works. Look at the kilo video. It has underwater video of the boat hovering. Going up a bit. Then down a bit. Backwards. Forewords. Like an underwater blimp. It works. Works well.

End of story.

I'm sure a suitable replacement pump can be found. I'm sure Art has come up with something, Time to do some research here men.

Steve

[Subculture]

Another solution is to use a waterpump. Keep the bladder, but pump water into it instead of air. Keep the ballast tank sealed, except for a vent into the dry area of the cylinder. As the bag fills with water the air will compress, and help the boat to blow ballast when you reverse the pump.

Andy

I'm sure a suitable replacement pump can be found. I'm sure Art has come up with something, Time to do some research here men.


It just takes some time and determination. 15 min and I found this site as a potential supplier for the micro-pumps

http://www.mpja.com/viewallpict.asp?dept=156&main=

Seems ok to me though I'm sure there is many more. Come on guys... get off your duff and look for things.

Dan

[tabledancer]

I have never had a problem with Daves RCABS system in my boat.It seems to work to good sometimes,all it takes is a very short blow to surface,and a quick release of the air from the bladder to submerge again.I can`t understand why so many people are having a problem with this system.Or do many people choose to do things the hardway always?
TD :wink:

[samreichart]

I emailed BigDave the other day asking about anyone's trying RCABS on something as long as my Type XXIII - about 55 inches. I would like to use something like RCABS for this model. I was considering Jeff LaRue's "hybrid" Engle system he's got in his Seehund, but I'd like to keep the costs down. Additionally, from an engineering perspective, I'm a total dweeb. So, I'm looking for easy and somewhat inexpensive myself. And, I need 5 channels, so forward planes operational, with an APC type device fluttering the rear planes.

Anyone try RCABS on anything this large???

Sam,

This boat is 48 inches and uses BD's new 3 inch RCABS-R water tight compartment. No problems man.

http://www.sneill.com/wtc/wtc.wmv

steve

[uboot]

I haven't got it in the water yet, but look at my web page in the subcommittee (bob_eissler) for the RCABS system I'm using. The bladder & pump come from electric blood pressure cuffs (check Walgreens,Walmart). I tryed using a windshield washer pump, worked fine on the bench but it was too slow for the vol I ended up with. The transmitter is a Futaba with PCM, it has a 3 position switch & with the travel set by the transmitter, it works great.

[Subculture]

My experience of model submarines tells me that for trim control, the piston tank has no rival.

Compressed air is extremely efficient at moving large quantities of ballast, so is especially well suited to larger boats and/or those with high freeboard.

It also has the advantage that it has a built in failsafe, except in the instance of RCABS.

I dislike this implementation of the compressed air ballast system, as it requires the operator to start the pump to surface. I prefer to use the pump to submerge, that way you only have to release a valve to surface.

Not 100% failsafe, but as near as you're going to get.

Mix compressed air with piston trim tank control, and you have the best of both worlds.

Andy. If it's trimmed right no matter what you use it should float back to the very top of the sail even if everything fails. That is if the WTC doesn't leak. Then no matter what you use your fucked and have to go swimming.

If you've seen my Kilo video then you know I can near rival the piston. I can hover. Raise up or down without ever hitting the surface. Really. Oh and I have never had it fail. Not yet.

Steve

[Subculture]

Ah, dynamic diver then. ;)

I like to run my boats slightly negatively bouyant, and get them to hang in the water.

It's a whole heap easier and more repeatable with a piston tank than with compressed air.

Andy

I'm one of the few that like dynamic divers. It's simple. Has a built in fail safe of sorts, no gas, no compressed air.

Steve

[tabledancer]

My boat has a failsafe with the RCABS SYSTEM by using the SubTech SES 3 switch to turn on the pump if it looses the signal for any reason.And it does work as proofed last fall in an incident I had.I fill that this is a very good and simple system,"if I can operate it and repair it as a newbie you know it`s good".
TD

[Subculture]

Yeah, but what happens if your battery dumps it's charge when you're underwater?

Probably not so much of an issue with a tiddler of a boat, but for something bigger................

The addition of a voltage monitor would help alleviate that problem.

I'm not knocking the simplicity of a compressed air system like RCABS, but simplicity has it's limitations. A Model T is simpler than a Rolls Royce, but the latter will give you a smoother ride.

Andy

[JWLaRue]

I have to agree with Andy here on the piston system. I built a custom WTC that uses a piston for the ballast system for my 1/9th scale Seehund. I can dial in the depth I want it to hover at and put it on the bottom if I just want to lurk for a while.

The next 'best' system for controllability (IMHO) is the OTW dive system. This is a water pump-based system that has a sealed ballast tank that allows the air to 'escape' into the dry space....just like the piston system. The included electronics have a built-in failsafe whereby if the voltage drops below a certain point, the system automatically empties the ballast tank and won't allow the operator to re-submerge until the battery is refreshed.

But no matter what ballast system is used.....it's all about having fun, eh?

-Jeff

[magpie]

I'm sure a suitable replacement pump can be found. I'm sure Art has come up with something, Time to do some research here men.


It just takes some time and determination. 15 min and I found this site as a potential supplier for the micro-pumps

http://www.mpja.com/viewallpict.asp?dept=156&main=

Seems ok to me though I'm sure there is many more. Come on guys... get off your duff and look for things.

Dan
Here-Here! We don't need to panic- things have ways of working out. (Sorry to but in)
Jason

[samreichart]

I have to agree with Andy here on the piston system. I built a custom WTC that uses a piston for the ballast system for my 1/9th scale Seehund. I can dial in the depth I want it to hover at and put it on the bottom if I just want to lurk for a while.

The next 'best' system for controllability (IMHO) is the OTW dive system. This is a water pump-based system that has a sealed ballast tank that allows the air to 'escape' into the dry space....just like the piston system. The included electronics have a built-in failsafe whereby if the voltage drops below a certain point, the system automatically empties the ballast tank and won't allow the operator to re-submerge until the battery is refreshed.

But no matter what ballast system is used.....it's all about having fun, eh?

-Jeff

yeah Jeff- your system's a beauty, but 'm feeling like I'd be overmatched with the engineering (and the cost too). obviously, Bob's system would be a great match for the XXIII too; but the exchange rate...
damn. not sure which way to go with this.

[jcopter]

So Hey
Thanks for all the info Sorry about calling it "RECARBS" brain failure,
so now back to my initial request, I guess the answer is, that Maybe big dave still has some of his pumps left? I was just wondering about the Aquarium pumps, "Did'nt know if anyone had tried this, and I know that the RCABS system works-- just wantsd to get a pump with out breaking the bank or a blood preasure monitor, cus they are like 50.00 or so so I'l give dave a shout
Thanks
jack

[Bigdave]

Guys!
I never said you could not get the pumps! I can still get them, and stock them. It is just that they will not sell in small lots any more. I buy them in large quantities so it is not a problem for me. I do not know what their minimum buy is now. BD.

[jcopter]

Dave has my kit ready, so sent the money out today, cant wait to see it !!! I'm looking forward to this build as it is my first RCABS system. after I done with the typeVII I will move on to my Seawolf and use the info learned to build it (should be quite easier)
Thanks to all
Jack

Sam,

My 1/48 scale scratched (with the help of Merriman's Skipjack hull) Washington class. It's a little over 48 inches long and works like a charm using Bigdave's new 3 inch WTC (WTC name created by David Merriman III).

The other nice feature about RCABS is that you can raise up or down bit by bit with proportional control unlike propel. See the Kilo video.

http://sneill.com/kilo/kilo2.wmv

and the GW video.

http://www.sneill.com/wtc/wtc.wmv

Steve

http://img166.imageshack.us/img166/5710/571b8tx.jpg (http://imageshack.us)

http://img166.imageshack.us/img166/6247/afterrun16kn.jpg (http://imageshack.us)

[Albion]

Sam,

My 1/48 scale scratched (with the help of Merriman's Skipjack hull) Washington class. It's a little over 48 inches long and works like a charm using Bigdave's new 3 inch WTC (WTC name created by David Merriman III).

The other nice feature about RCABS is that you can raise up or down bit by bit with proportional control unlike propel. See the Kilo video.


I agree that the RCABS is proportional, however a bag is compressible. and should you have a temporary looss of control and a big dive you risk the bag being compressed and losing your neutrality. Piston tnaks are fixed volume and dont have any risk of this. Its a remote posibility i agree but the fact remains

I agree with you. Pistons are the way to go if possible.

I never dive deeper than 8 ft. anyway and that's in a pool. In a lake if you get to that depth you lose site of the boat anyway. Not comforting at all.

At 8 ft. I have no problem sitting on the bottom like a rock and then bringing it back to the surface again.

Steve

Who would like a piston! At lease one. ;)

[Subculture]

You could easily combine a very small piston trim tank with RCABS, and obtain the best of both worlds.

There are ready built, dirt cheap small piston tanks- they're called syringes.

Add a small motor and gearbox to the syringe. Have the air bag fully evacuated (so it is no longer compressible), this should bring the boat to just slight positive bouyancy. Then use the piston trim tank to deal with the last part of the trim. There you have a very nice, cheap and largely failsafe system.

Andy

What a great idea Andy.

Thanks,

steve

[Subculture]

No problem Steve.

Also if you use a good, high torque servo to activate the piston tank/syringe, you have a cheap and proportional ballast system.

You can use a cheap rack and pinion to convert the rotary servo motion to linear motion.

If you had two of these mounted either side of the main ballast tank, then you also have built in control of longitudinal trim.

This means no more mucking about with little lead weights.

Andy

[Boss Subfixer]

A good source for syringes believe it or not is a cookware store or cookware section of a dept. store. Look for the better marinade injectors for turkey fryers. They are designed to screw together, even the plunger and come apart for easy cleaning. Match the thread size for the plunger and your off and running.

[Steve S]

" The next 'best' system for controllability (IMHO) is the OTW dive system. This is a water pump-based system that has a sealed ballast tank that allows the air to 'escape' into the dry space....just like the piston system. The included electronics have a built-in failsafe whereby if the voltage drops below a certain point, the system automatically empties the ballast tank and won't allow the operator to re-submerge until the battery is refreshed.

But no matter what ballast system is used.....it's all about having fun, eh?

-Jeff "

I have questions about the operation of the OTW ballast system...perhaps someone knows exactly how it operates...

I was on the OTW site looking at their ballast system, unfortunately they don't give much information on how the thing actually works.

How does the air "escape" into the dry space of the WTC? And how does this air re-enter the ballast tank chamber after the water has been pumped out of it? I can follow how the pump is used to push water into the tank and draw it out, but I don't understand where the air is going and how it is moving about in the system. Is the ballast chamber vented to the WTC and somehow, when filled with water, something prevents the water from passing thru the vent line to the WTC?

On the other hand, the RCABS system has a ballast chamber that is vented allowing water to fill into it from the wet area inside the sub. There is an air pump that pushes air from the WTC, into the bladder (which is inside the chamber). When the bladder expands, it forces the water out of the chamber, hence filling it with air. Then a servo controlled valve releases the air from the bladder which finds its way back into the WTC, letting water refill the ballast chamber. Is this how the RCABS system works? I came to this conclusion after watching Steve's Kilo video...as he shows it in operation, but didn't explain what was actually happening (how it works).

Wouldn't a ballast system only need to give the sub positive and neutral bouyancy and not negative? Positive on the surface, then change to neutral, and use the forward motion of the sub and dive planes to submerge and then head back to the surface, and change to positive to completely surface back to waterline. But unlike a typical dynamic diver, there would be no positive bouyancy force that the motor and dive planes need to "fight" to keep the sub underwater... It seems like negative bouyancy would only be required if one wanted their sub to staticly submerge using ZERO forward or backward motion, but would not be required to "hover" in place underwater.

Steve

[Subculture]

Here is a simple little drawing I rustled up on 'paint'.

http://img68.imageshack.us/img68/7359/otwsystem8yl.th.gif (http://img68.imageshack.us/my.php?image=otwsystem8yl.gif)

To submerge the servo controlled valve is opened and the pump started.

Water is pumped into the central ballast tank, and the air is displaced into the forward compartment via a small hole located above the probes, where it is compressed.

When the water level reaches the probes the pump shuts off, by this time your boat should be beneath the surface.

To surface, the pump is reversed, and the water sucked out of the tank, the compressed air helps the tank empty, especially against the increased water pressure.

The system works well. One small drawback is that the tank has an exposed water surface, so it's essential that the tank is baffled to avoid the unpleasant effects of sloshing.

Some people like to trim their boats so that they are negatively bouyant. Others prefer a little positive bouyancy.

Neither are wrong, it's just down to personal preference.

[Steve S]

Thanks for the clarification on the OTW system, Subculture.

There appears to be a servo release valve for the air bladder in an RCABS system, but is there also a servo valve on the WTC side of the air pump in the RCABS system? Or does the air pump itself hold the compressed air inside the bladder or the WTC (when the pump is idle, not pumping)?

[Subculture]

The RCABS system works thus-

You have three major components- a small compressor, a schraeder (tyre) valve controlled by a servo and an air bag.

Before using your sub, you use the compressor to inflate the airbag. To do this the compressor draws air from the compartment it resides in, thus leaving a vacuum in that compartment.

To submerge, you operate the schraeder valve, this allows the air from the air bag, back into the compressor chamber.

To surface, just operate the compressor once again to refill the air bag.

A variation on this is to inflate the air bag at the pondside, but use a valve to allow the compressor to draw air from outside. this only has to be done once for each outing. Reversing the compressor sucks air out of the bag, and this is then stored under pressure in a sealed compartment or tank.

When you wish to surface the schraeder valve merely lets the compressed air bak into the bag.

This is much better implementation in my view, as it's more failsafe. But most people use the slightly simpler system, with much success.

[John Anderson]

A thought on refining RCABS.
Instead of the pump being used to inflate the bag reverse the sytem to this.
To dive the compressor DEFLATES the air bag and Pressurizie the air flask. A one way check valve prevents blow back thrugh the compressor when the tank is full. To surface A high torque servo opens a solnoide valve from the tank to the bag. Thr Bag more rpidly inflates givong a far more realistic surfacing. All of the above gear is used in R/C Pneumatic landing Gear. By default the valve can be set to fail open when power is lost. This way a R/C sub would automaticly surface without power to pump or anything else. Plus if the system is set up on the surface there is little chance of poping the bags which is completely feasible doing it the other way around.
John

John,

It's been done by BigDave and I'm currently testing it in my GW with perfect results. It's called RCABS-R.

Here's a pic after running my GW. It's a 3 inch WTC. Really I don't know why more people don't use it. A lot of the old time builders have turned their noses up at it. Question whether it really works or not when it has been ever since Art Broader started showing off his design for it.

Again. One of the nice things about it as is evident by my Kilo video under water. Is the boat will very near hover. You can change depth gradually and surface the same. Near proportional control unlike gas.

I'm sold on it and if you look at the top of RC subs forum here you will see many videos I have posted that demonstrate who it works both in operation in the boat and on the bench. I don't think many of you have seen my videos based on a lot of the questions I see here and in other threads.


steve

P.S. One more time. Here's the Kilo video but you can find all of them at the top of the forum, RC sub Modeling.

http://sneill.com/kilo/kilo2.wmv


http://img241.imageshack.us/img241/3100/afterrun18wt.jpg (http://imageshack.us)

[Subculture]

That's the system I described in the second half of my post. It's been used by modellers here in the UK for years (adapted Darnell kits).

Plus you don't need a high torque servo to activate the valve, any old servo will be upto it.

You can refine the system further by doing away with the air bag completely and fitting a sealed tank.

Many ways to skin a cat.

Andy

Yes indeed Andy.

Steve

[tabledancer]

I have a question.Instead of using a servo to control a Schradder valve to inflate your bladder could you use a Clippard valve or some other type of electronic valve to replace the Schradder and servo?Then you could use this for your failsafe also by having a valve that is normally open.Is that fesible?
TD

[Bigdave]

Hi TD,
My R system uses a clippard valve and a SES-3 so the failsafe is built in. I retrofitted my testing prototype and I like it better. There is also a built in failsafe because the pumps are one way, but they do have a very small leakage over time. If the sub sinks with this system and you have a total power failure the air will very slowly return to the bladder and hopefully bring the sub up. :D BD.

[tabledancer]

Dave,
Is it possible to change over my system to the your "R" system just by changing out the pump,becauce I`m using the Cippard and SES-3 just like you said.I never used the Schradder and servo like a few of the guys seem to have done.
TD

[Bigdave]

If you are talking about the V11, No.
My R cylinder was designed around this type of system. You can't switch from one to the other. It requires a separate pressure chamber to deposit the air into. The systems are similar, but totally different in application. BD.
http://img382.imageshack.us/img382/3716/rcabsr9vi.th.jpg (http://img382.imageshack.us/my.php?image=rcabsr9vi.jpg)

[Steve S]

Dave,

Is the Clippard valve your referring to a Clippard Minimatic electronic valve? If so, what is the part number for the valve, and does it have proportional control?

I assume the SES-3 electronic switch is used so the air pump and clippard valve can be both controlled via one radio channel, and it apparently has a fail safe circuit that senses loss of radio signal and will open the clippard valve when signal is lost.

Steve

[tabledancer]

It was just a thought,but thanks for the good info anyway. :wink: I think I finally got it rite so I don`t need to change the wtc in U-407.I assume that all your kits are now setup with the newer system.


By the way,how is the new WTC with the 2 motors for the Revell Gato coming,when the kit is released you can count on an order from me 8) .
TD



PS How are you feeling since you got out of the hospital

[Bigdave]

Steve,
You are correct in your post on the clippard system. The valve is not proportional though, just open and closed. I am not sure on the part number but it is available from http://www.mikessubworks.com.
TD,
I am still working on the two motor cylinder. So far so good. BD.

Steve,

If you watch my Kilo video you'll see that even with off and on it is very proportional. All you do is bump bit by bit either the switch the for the pump or the schrader valve. Little taps on the gimbals work well as seen in the video.

The kilo under water comes into frame and stops. Goes up about a foot and holds that depth and moves off. Plus there are several shots underwater showing this during the night sequence.

KISS. It always works best.

Steve

[tabledancer]

Steve,
That just the way that my system works,just as you decribe,"BUT"you must be careful on your transmiter choise.I am using an AirTronics VG 600A and the failsafe has worked fine for me.Some of the crew has had problems with this radio and the SES-3 failsafe system.Check out the the posts on this subject elsewhere on this forum a couple of months back.I am using Daves original system which works great but from what I`ve read his new system works better.What the Fearless Leader wrote is the straight skinny,my system operates the same way except that mine is set up a little bit different.
TD

The only boat I have that has a FS is the 17 with the D&E 3 inch WTC. And that is operating on a Hitec radio. NP.

I just trim them so the very top of the sail is above the water. I call it the chicken trim.

Thanks TD,

Steve

[Bigdave]

Chicken Trim!! :shock: PUCK-PUCK-PUCK!!! I would call it something else :roll: Ha!!

Smart trim?

LOL!

steve

[Bigdave]

Starts with a P, ends with a Y. Trim. :shock: :lol: :D :P :wink:

Oh ya.

steve

http://img512.imageshack.us/img512/5254/53646526catgun1ro.gif (http://imageshack.us)

[Subculture]

I think 'controllable' or 'easy to trim' are a better turn of phrase than proportional, to decribe the RCABS system.

It's a bit misleading to describe RCABS as proportional.

Andy

Has anyone ever tried multi-valves, one for fast and one for slow.

http://img83.imageshack.us/img83/2470/dualvalve9aa.th.jpg (http://img83.imageshack.us/my.php?image=dualvalve9aa.jpg)

[magpie]

Big Dave old son!
Have you had a chance to work out a system for the new Blueback of Steve's yet matey? I'm still interested in using your system as I like the pump idea as apposed to the gas can that needs refilling etc. Do you have a ballpark idea of what it will be worth also please Dave?
Regards
Jason

[Bigdave]

Hi Jason,
I sent a prototype Blueback cylinder kit to Steve a few weeks ago. He will eventfully be testing it and hopefully I got it right. I will be testing it in my kit too. It is a variation of my Seawolf cylinder. Larger for the increased air volume needed for the RCABS in the Blueback. BD.

[magpie]

Thanks Dave. I sent you another email just now before seeing this post.
That new site is a good idea!
Jason

[magpie]

Dave.
You probably already watched this clip of the final trial of my Blueback RCABS, but in case not, here it is http://www.youtube.com/watch?v=VWal-QqcIqk
She's all finished and the RCABS is working a treat! Much quicker than the piston tank I put in my #7 and cheaper too!
I love it. The way I set it up with the smaller cylinder up front is just enough air for the job. She sinks to the bottom and floats almost right. About the same height as John's Barbel with the D&M propel wootsie anyway. I'm happy.
http://img182.imageshack.us/img182/2466/bbfinaltrial10fy3.jpg (http://imageshack.us)

[John Anderson]

Very nice run Jason!
I notice yours also takes on a down bubble when you crank up the throttle on the surface raising the screw to where it ventilates. Ah well it's fast submerged where it matters!
Love that RCAB! I wish I had it last Saturday when I was running her in front of an audience. LOL ran out of gas real fast.
Again nice run!
John

[Bigdave]

That is great! I am glad it has worked out for you. :D BD.

[John Anderson]

Okay folks I hear so much about a water bladder system cans ome one post shots or sketches of one and a simple explantion of how it works.

Second what about using the aircompressor from those very small car emergency setups? I mean without the bulky plastic case they are quitre small in size. Or how about the small compressor for those car airhorns ?

[magpie]

Art started with a car pump and evolved to the BP monitor pump. They're really cheap and tiny!
BTW John, it was mainly the APC set wrong that made her dip her bow. I have it on velcro and didn't set it right before assembly. I was driving her with the plaps up manually and occasionally let the stick go, hence the bow dipping. I was intensionally diving and surfacing as the water is so muddy that you can't see her at all under water and need to come up for a look every few metres or risk a mud dive!
Dave's site
http://www.frontiernet.net/~bwelch/
has a pretty good description of the RCABS system. His banner is all over this site. BD Designs ....
Thanks BD and John!
Jason

[Subculture]

Okay folks I hear so much about a water bladder system cans ome one post shots or sketches of one and a simple explantion of how it works.

Second what about using the aircompressor from those very small car emergency setups? I mean without the bulky plastic case they are quitre small in size. Or how about the small compressor for those car airhorns ?

I can answer this, seen all the systems you describe.

First I'll answer the question about the air compressor. Many modelmakers here in the UK have converted these units for use in model subs. Usually they've used it to replace a USE steam pump on an old Darnell models kit. The latter use an air bag system with a seperate reservoir.

The stock motor is usually replaced with a speed 400 equivalent, which is powerful enough for the application, but draws less current than the stock Speed 500 style motor.

They work well enough, but are rather crude, and not well balanced. So they need to be softly mounted in the sub to damp vibration.

A better alternative is to get an old i.c/glowplug engine and machine a new one way valve to screw in place of the glowplug. You will need a lathe to achieve this though.

To answer your question about the water bag system. These essentially use a pump to pump water into a collapsable bag. Pumps used are usually types which can run bi-directionally, i.e. geared pumps and perstaltic pumps. The former require a servo controlled valve to prevent back flow, perstaltic pumps however are self sealing.

The disadvantage with perstaltic pumps, is that they can be slow and not very efficient. They also tend to be more expensive than geared pumps.

Most people house the bag in a sealed tank (with some air space). This offers three advantages

1. The air compressed in the sealed tank helps empty the tank when surfacing.

2. If the bag splits through over-pumping it won't flood the electronics.

3. The compressed acts as a spring which helps to prevent overpumping.

Andy