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RCABS LESSON LEARNED - THE HARD WAY!

R/C Submarine modelers

RCABS LESSON LEARNED - THE HARD WAY!

Postby Bill Rogers » Tue Nov 18, 2008 3:25 pm

Yesterday, after several months, I finally finished my RCABS and could hardly wait to get my boat in the tub to check it out. Since I hadn't trimmed the boat I thought the best thing to do would be to start off with the bladder inflated when I put the boat in the water.

So I turned on the TX, switched on the ESC and tested the systems. Everything worked fine during the bench test. Bladder inflated and deflated just as designed. Then I carefully inserted the forward end cap, vented the cylinder thru the Schrader valve, and did a visual check of the O-ring to ensure a tight fit. Some of you may already see the problem.

The boat sat level in the water and I thought great, I won't have to worry about surface trim. Then I signaled the Clippard valve to vent the bladder. The boat started to dive, slowly at first then faster, bow first.

That's when I noticed air bubbles coming up as the bow dropped even faster. A signal to the pump started to bring the boat up then quickly to the bottom of the tub.

Brought the boat out of the water, out to the bench and opened it up. I found the forward end cap off, and water in the cylinder. While letting the blow dryer run on the parts I sat down and started writing out step by step what I had done and what I saw happening.

It didn't take long to realize I had inflated the bladder with the end cap off the forward cylinder that housed the air pump and the Clippard valve. When I put the end cap into the cylinder and vented thru the Schrader valve the bladder pressure was greater than the pressure in the cylinder. Venting the bladder thru the Clippard valve overpressured the cylinder pushing out the end cap and allowing water to enter.

The story doesn't end here though. By continuing to run the air pump after water entered the cylinder, I had pumped water back into the bladder!

Had I installed the end cap before inflating the bladder, there would have been a pressure difference between the cylinder and bladder that likely would have equalized when the bladder was vented to dive the boat.

I was lucky in that I was able to save the Clippard valve, the Jomar switch and the air pump. The ESC however was damaged beyond repair.

Bill Rogers
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Postby Art Broder » Tue Nov 18, 2008 6:10 pm

Sorry you learned something the hard way. Inflating the bladder from open air can lead to other overinflation problems, as there usually is no pressure sensor, to shut the pump off.
Another (almost opposite) problem to avoid, is to NOT remove the bladder hose from the end cap when bench testing, in order to deflate the bladder for another inflation test. Eventualy you will run out of air in the closed cylinder, and erroneously think things won't work. It is a Recirculating system, remember, so signal the RCABS release valve inside the cylinder to release the air back in from the bladder.
In the closed system, if the bladder does not deflate quickly and completely, when the RCABS release valve is opened, then there is an air (and potentially a water) leak in the cylinder.
Art Broder
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RCABS- It's easy to control your own bladder!
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Postby Bigdave » Tue Nov 18, 2008 6:29 pm

One good thing to do no matter what kind of system you use is to have something to keep the end caps on. :D
Having to rely on the O-rings is not a good idea. :(
I always try to have some kind of stops on both ends of the cylinder to keep thing in place. :?:
Hatch sealing tape (Hockey Tape) works well too. R/C boat guys use it for sealing the R/C compartment hatches on surface craft (Targets). :shock:
It is waterproof and comes off easy but sticks very well. 8) BD.
David Welch
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Postby U812 » Tue Nov 18, 2008 8:02 pm

YES! Hockey Tape has saved me every time. You can get it from sports supplies stores. Works like magic in water. Perfect ever time. I never go diving without it.

Steve
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Postby aquadeep » Wed Nov 19, 2008 9:32 am

I would sugest that you use my WTC ,the caps dont come off unless you want them to and you wont have any expensive surprises ! :shock:

An inexpensive way to protect what is.

Dave :D
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Postby U812 » Wed Nov 19, 2008 1:15 pm

Here we go angain. :roll:

U812
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Postby Bill Rogers » Wed Nov 19, 2008 2:50 pm

Thanks for your comments Art, BD, Steve and Dave. I'll get back to work on it, a bit smarter this time.

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Postby Albion » Wed Nov 19, 2008 10:29 pm

[quote="aquadeep"]I would sugest that you use my WTC ,the caps dont come off unless you want them to and you wont have any expensive surprises ! :shock:

An inexpensive way to protect what is.

[quote]
Do you actually have these operating?
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Postby aquadeep » Thu Nov 20, 2008 11:24 am

Yes one is in final trails and another larger one is in construction.
Another very large 3.5 ft WTC for the Robbe Type XXI is being developed also.

Will soon post results.

This WTC can also be used with CO2 and R cabs systems.

Also the ballast tank area can be opened and complete acsses is available and adjustable in volume with just a twist of the tube!
Unlike other WTCs the end cap must come off and inner components removed and another bulkhead removed very carefully as not to crack the thin walled plastic.

Sorry for the ( :( here we go again)

Call me at 1 352 351 2547 5 to 8 pm EST. for more information.
Dave :D
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