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Author Topic: Sheerline Akula- cheap dive system  (Read 2073 times)

EJL

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Sheerline Akula- cheap dive system
« on: December 13, 2019, 07:13:53 pm »


 The Akula was fitted with an old Sheerline dive system. The black pipes shown in the following photographs are the front and rear chambers from the original system. I scrapped the centre sealed container. When I bought the sub recently it came with an empty craycraft clear acrylic dive module. I used one of the chambers as shown in the photograph. The centre chamber now contains a thick rubber rugby ball bladder (£3 from ebay).
Inflation and deflation is achieved using two cheap air pumps from china (£3.50p each.) They operate independent of each other, one to inflate, the other to deflate. Two micro switches fitted to a servo. Each pump had been fitted with a small solenoid air valve to prevent back feed when the chamber is under pressure.  (Solenoids £3 each from china). Before the sub is placed in the water the green valve outside the air tight chamber is opened and the inflation pump used to fully inflate the bladder. The green valve is then closed.  Boat is then ready to go into the water. To dive the deflation pump is used to move the air from the bag into the clear acrylic chamber shown.. System works extremely well and has cost me less than £30.
Why did I do it- simple the original Sheerline system was not very good.


 
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EJL

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Re: Sheerline Akula- cheap dive system
« Reply #1 on: December 13, 2019, 07:14:43 pm »

All the working parts
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EJL

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Re: Sheerline Akula- cheap dive system
« Reply #2 on: December 13, 2019, 07:15:27 pm »

The central chamber.
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salmon

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Re: Sheerline Akula- cheap dive system
« Reply #3 on: December 14, 2019, 05:26:28 pm »

Very creative!
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Subculture

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Re: Sheerline Akula- cheap dive system
« Reply #4 on: December 14, 2019, 10:15:12 pm »

It's a variation on a recirculating air ballast system, seen it used on a few models. The main disadvantage is you can't trim for different water densities like you can with some systems. Until the availability of inexpensive small diaphragm pumps from the far east, which first started appearing about 15-20 years ago, modellers either had to adapt tyre inflators, old glowplug/diesel/steam engines, or if they had the tools and skill set make their own pumps. This is why water pump systems gained popularity, as small pumps were readily available and needed no modification for use. Also water pumps can be controlled a bit more easily if you want a trimmable system.

You'll quickly find that there is no such thing as the perfect dive system, you trade off the pros and cons depending on your priorities and preference.
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salmon

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Re: Sheerline Akula- cheap dive system
« Reply #5 on: December 14, 2019, 11:10:08 pm »

Andy,
I so agree with you, they all have their trade offs. I enjoy when someone gets creative. There is very little new under the sun when it comes to rc submarines, it is just the flair we put into it that makes it unique.
Peace,
Tom
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Fred Ellis

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Re: Sheerline Akula- cheap dive system
« Reply #6 on: December 15, 2019, 09:04:38 am »

Hi


i have just started to read your post, to me it look like the system we used to call the "Darnell system" but with two pumps,


As Andy said you will have trouble with the trimming, as the bladder will not inflate the same way every time, that is why most of us went over to water in the end.
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Re: Sheerline Akula- cheap dive system
« Reply #7 on: December 15, 2019, 11:37:27 am »

I think the bag should inflate the same each time- it's constrained by the circular tank, which will act as a 360 degree cuff, plus the fact you have an airtight pump acting each way should ensure a good strong evacuation/inflation each cycle.

When I was referring to trimming, I meant the ability to account for the 1% change in water density depending on temperature and mineral content. If your boat displaces say 5kg, then that amounts to just 50ml difference. Fullsize submarines incorporate separate compensating tanks to trim for different water density, these were made larger still on boats which had to operate in both salt and fresh water. Few model submariners incorporate compensating tanks in their boats, as it means making a separate ballast system, but they are out there, often on larger model subs.

Piston tanks with some form of feedback on position allow the compensating system to be built into the main system. With pump systems this is more difficult, as they tend to incorporate an exposed water surface, which is difficult to get a reliable point of feedback, so these systems tend to be open ended feedback- e.g. mark one eyeball!
With the system Ernie has here, he should run it with the bag empty when submerged, and if the boat is bit light or a bit heavy, add or subtract a small amount of weight (e.g. lead weights) to compensate.
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Fred Ellis

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Re: Sheerline Akula- cheap dive system
« Reply #8 on: December 15, 2019, 12:40:43 pm »

Andy


As one who has gone down most of the routes in my time, it all boils down to what you fill the most comfort with, I myself like having a solid B/T which I can pump water into thereby compressing the air into the top of the B/T, then using the air to blow out the water when it is time to surface.


As they say "You pay your money and takes your choice".

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Martin (Admin)

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Re: Sheerline Akula- cheap dive system
« Reply #9 on: December 15, 2019, 01:10:50 pm »

Hi

i have just started to read your post, to me it look like the system we used to call the "Darnell system" but with two pumps,


Me to!   :-)
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Re: Sheerline Akula- cheap dive system
« Reply #10 on: December 15, 2019, 01:48:52 pm »

As I said in my first reply- pros and cons to each system.

With the sealed tank water pump system, if you want the pump working pretty efficiently, you can fill a tank around 50% full, you can go further but the pump will pulling a lot of current going by tests I did. So with 50% filled tank the pressure inside will be 14.7psi above atmospheric. The tank needs to be sturdy to withstand such pressure, and you also have an exposed water surface to cope with. Unless well baffled the sloshing tends to upset the boat's c.g, how much depends on the stability and speed of the boat, and also the length of the tank- short is better.

I found boats with this system behaved a bit 'wooly' with regards to pitch stability compared with boats which have a system that eliminates sloshing, bit like how a car with worn steering bushes will wander a bit on the road. Slower subs aren't affected so badly, but if you have anything a bit spirited, it can get interesting.

One method I've seen which largely eliminates this is to employ a horizontal baffle in the tank so that once the water reaches that plate, it holds the water in place. However most systems I've seen have vertical baffles only.
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