Revell typ VII/41 RCABS (Big Dave) build

[Dolfin]

Hallo friends,

When Revell released the Type VII 1/72 submarine I decided to build the boat static diving. I bought the Dave Welch conversion kit in 2007 yes 2007 and i had no idea how it works. The kit was in the basement (no time due my job)until the beginning of this year, but now it was time I started to build.
It started with a fault with the two motors (small Mabuchi or so) the motors were too weak because of the double seals. Next failure I bought two small geared motors which were too slow again. I came up with the idea of a brushless motor with a gear like the Brüggen Conversion. The first brushless inrunner was too strong above 3400kv the seals were extremely hot. I read about brushless in rc subs max 1400kv so I found the right one now i am very happy with it. Is a Roxxy outrunner and Roxxy ESC which is programmable forwards and revers.
I made the seals twice opposite because of the vacuum pressure so I thought.

There is relatively little air in the bladder, is that enough? Does anyone know? I'm thankful for any help



Here a few pics and video

https://youtu.be/kpLyMM4iv2Q

[salmon]

I thought Big Dave systems started with bladder filled and pumped air into cylinder. Just the opposite of what you got going there.

[Dolfin]

Hi,
Are you sure? I’m a little bit confused now how it will go. I can remember in the description that the air from the WTC goes into the bladder and it gets vaccum inside when you open the schrader valve it sucks the air back. I hope I’m right?
Now I have to look for the CD that came with the kit. I hope I find it.

Best regards

[Ralph --- SSBN 598]

I have this system in my George Washington 1/144.
Dolfin, your observations are correct.
There is a vacuum pump in the cylinder that pumps air from the cylinder in to the bag.
A Schrader valve is opened the vacuum in the cylinder pulls the air back in to the cylinder from the bag.
The vacuum in the cyulinder also hold the end caps on.
-------
If the air started in the bag and was pumped in to the cylinder, the pressure build up would pop the end caps loose sinking the boat almost emediately unless there are retaining bolts or something to hold the end caps on under pressure.

[Dolfin]

Thank you! Ralph
I am glad that everything is correct. There is relatively little air in the bladder, do you think that's enough?

[Ralph --- SSBN 598]

I have a Schrader valve on the front of the cylinder to access the power switch.
The black plastic parts are so I can get hold of the end cap to remove it.

I also use this valve to suck ot the air in the cylinder removing all air from the bag.
This is the state which the boat is trimed to top of sail above the water when not moving.
The turn on the vacuum pump to fill the bag to surface and raise the boat up to the water line.
Any air in the bag when the Schrader valve is opened and the vacuum empties the baga is air you have to ballast to dive with extra weight.

Boat shown without the bag which sits above the center section of the cylinder.


This is a Dave Welch cylinder.

[Dolfin]

Wow, thank you so much. There are very good features very helpful. How you suck it out with an air pump? As I can see the valve from the Schrader let you only blow in? Or I’m wrong?
The plastic parts are a very good idea because with a screwdriver in not really a good option.

Greetings

[Ralph --- SSBN 598]

I have a short piece of fuel hose and there is no parts inside the Schrader valve on the end cap.
It is just a tube with threads for the valve cap.
I fact I drill the inside of the valve body a little bigger to get my custom key in to operate the on/off switch.

[Dolfin]

Ok, I understood now and from there you suck out all the air from the bladder with a tube which you can connect.
Sorry about so many questions from me I’m almost a newbie. I’m reading a lot and learning more and more. So I can not be frustrated and the hobby is more fun.

Many thanks take care.

[Ralph --- SSBN 598]

Everyone starts some where.
Your questions are no different than mine where some 30 years ago.

[secrtwpn1]

Wait! What? It'll take 30 years to figure these subs out???????

[Ralph --- SSBN 598]

Farlan, that would be a "No" because so many before have figured out all the little details required and they can answer the questions.

We just need to ask questions and listen to those who have been doing this for so long.
We have Will, Mike and a few others to help in our little group.

My first working sub was built about 1991 or there abouts.
Late 60s and early 70s, I service in the submarine service, mostly in the yards during overhaul.
BAck then the model systems where based on the real boat systems.
Your Blueback is a high pressure gas ballast system. (much like real boats)
The eal boats had an advantage on trimming because they had ballast trim tanks.
One forward and one aft that water could be transfered back and forth to keep the boat level and used for depth control after the main tanks were completely flooded by adding water from sea or pumping overboard to sea.

I happen to have the system, Dolfin is working with and I will share what I can to help.

I got in to these boats about the time Freon was banned and a replacement had not quit been worked out, yet.
So I did not go with high pressure gas.
I went pumps both water and air and now I am going pistons.
Though I am having issues trying to make a piston sytem for a
small boats with small cylinders.

[Dolfin]

Hallo,
Testing the WTC in the boat fits perfect


A view with decks I’ll connect the front and rear deck with magnets. I think the middle deck I’ve to screw because of the bladder.

Now I need the Dumas dog bones couplers for the prop shafts because I have to slide the WTC to the rear to get it out. I have to order 4 from Bob.
@Ralph do you think I can instead of the Schrader valve a 1/8” brass tube to suck the air out, because I have no switch inside but I really like this idea. How I suck it out? Connecting a silicon tube?

THANKS a lot Ralph you’re really helpful.
TAKE CARE

[Ralph --- SSBN 598]

A brass tube will work.
You wilkl need to have some sort of cap for it to seal the water from getting in.
Remember, this system pulls a vacuum in the cylinder and that will try to pull water or air in to the cylinder when the bag is filled.

I use the tire Schrader valve because it has a threaded cap to seal the tube and I can get caps with a rubber wash in the cap that does the sealing.

[salmon]

Check out this site and see which version you have. I am confused because I have mine set up as a Reverse-RCABS.

https://www.frontiernet.net/~bwelch/ballast.htm

Not sure if it makes a difference or if the seals are put in differently with the different versions. Best wishes on your sub.