Robbe Type 7 8-ball project

[bigdave]

My fellow 8-ball Greg W (Mr Pita) has acquired a new project.
Let me tell you the story.
Greg was talking to Jim Smith at the Carmel event and Jim asked him if he would be interested in a Robbe Type 7 project boat.
Greg told him no but thanks.
Greg and I were talking and he mentioned the sub.
After promising to help, and design a ballast system and tech rack Greg told Jim he would take it.
I said it would make a nice project sub. And after it is done we can use it as a clubsub.
If we get a visitor that may be interested in model subs or someone needs a boat to run we have an extra.
Greg said Jim wanted to give the boat a good home.
Not to someone that would just turn around and sell it.
So about a week ago Greg received a package.
One semi built and semi complete kit.
Thank you Jim.
We will give the old girl the respect she deserves.
So far it is just gathering info on the kit and discussing how we will proceed.
I do have one request to you Bubbleheads reading this.
One of the parts missing from the kit is the rear deck.
If anyone is able to do a rub of the slots in the deck off your part or has built the kit with brass decks and wants to part with the stock rear deck please contact Greg or I.
Except for the control system the sub will be built stock.
So stay tuned sports fans. BD

[bigdave]

The main problem with the U-47 design was it has no ballast system.
So you have to trim the boat heavy and power it under to dive.
Standard dynamic diving yes, but as they wanted to keep at least a little surface trim Robbe needed to use larger motors to force it under.
This made the sub heavier out of the water, and a amphog when diving.
One of the cool things about the older subs, (I call them rigging subs) is they look cool out of the water with all the rigging lines and dodads.
They spent most of their time on the surface anyway.
So I like to get them at a high scale waterline.
To do this you need a ballast system.
The ballast system in the U-47 will allow for much lighter transport, and higher waterline.
And less powerful motors can be used to save on wattage consumption.
But as this sub will be used by novices too we want to incorporate the dynamic diving safety factor into the ballast design.
This means we will most likely use a decks awash ballast design. (DAWB)
Taking on just enough water to get the sub slightly north of neutral buoyancy.
Right now I am thinking a air pump system for this and am sketching out designs.
A properly trimmed out dynamic diving boat can be a joy to run.
Anybody that has seen DonO's Seawolf run can attest to that.
Plus you have the safety factor of drifting back to the surface.
(As long as you are not stuck)
So this is what we are thinking of now. BD

[JWLaRue]

BD,

I have a deck set (3 parts) for the robbe U-47. They're yours if you'd like to use them.

-Jeff

[bigdave]

Excellent!
Thanks Jeff!
I will email you for the particulars. BD

[Guest]

Vented fixed tank with a gear pump (Kavan or similar) under bidirectional control from an ESC or a servo with microswitches. Very simple and inexpensive.

[bigdave]

That is about as simple as it gets. BD

[bigdave]

In my surfing the Internet for all things U-47 I have found an interesting conversion.
The web site is in German, and I only know a few words of technical German from building many German kits.
But I like the ballast system they have designed.
I could not see an explanation of operation on the site.
But it's what looks (Just my observations) to me like a water bag, or IV bag and pump system they used to call it.
What is cool is they mounted it in its own assembly. Which can be used in different models like an Engel tank.
In fact I guess you could call it a Engel tank with a OTW type pump system.
There is a tube with end caps on each side with threaded rod stays holding it together.
On one end is mounted a water pump (Geared most likely) and a electronic valve.
Inside is a bladder of some kind. The pump fills and emptys the bladder using the valve to hold back the pressure.
OTW uses a hard tank with baffles in there system.
But it's built into the cylinder as one assembly.
This is just a ballast assembly that can be added to a dry hull boat or cylinder.
I would assume the tube is vented to allow more water to enter the bladder.
Now I can't confirm or deny any of this info as it is just my take on its operation.
Here is a photo of a U-47 conversion using this type of tank.
The company is Maximus Modellbau. They are actually mentioned in the March SCR.
(Another reason to actually join the Subcommittee)
Not just the website. Hint Hint!

[Guest]

I think a few modellers have had issues with the hull seal if the ballast system pressurizes the internal cylinder. A good upgrade is the bayonet lock, but something equally as efficient could be knocked up for a lot less, with the main plus points being radial o-ring seal, and removal of stress from the tech rack.

If retaining the original set-up, then the vented system has much to recommend it IMO especially if you're aiming for a high waterline when surfaced.

[bigdave]

Thanks Andy.
Greg has ordered the bayonet ring conversion for it.
It will make life much easier. BD

[bigdave]

I wanted to give an update on the progress of our sub project.
I have been able to get a few hours on designing and building my version of the water bladder ballast tank.
Parts have been acquired.
Gear pump, valve were found on EBay and are nice quality.
All the rest I had in stock. Cylinder parts, bladder, ESC, and associated gizmos.
So far testing has gone well.
Using my initial design change as you progress system. (IDCAYP) lol
You basically have a bladder sitting inside a Lexan tube.
On the front endcap is mounted a high pressure gear pump, and valve that supply the bladder with water ballast.
The valve opens and closes with the pump running in either direction.
Similar to the way an OTW system works actually.
Nothing new, just done differently.
The bladder will inflate with 850cc of water. The pump is stopped at that point by a plunger inside the tube mounted on the rear endcap.
The plunger hits a micro switch cutting power to the pump.
BTW The cylinder is vented to the inside of the subs WTC.
It has to be or the pressure built up will exceed the seals thus resulting in a POP.
(Trust me)
The system is controlled by a small ESC which runs the pump in both directions.
Fail safe will be provided by using a PCM receiver with failsafe built in.
I am still tweeting the design but I am happy so far.
It's funny as a variant of this ballast system was used on my first RC sub kit I bought in 1979. From ISPD models of Italy.
It has a pump and bladder system.
Just a different approach.
I will explain that system in another post.
Here are a few photos of my progress so far.

[bigdave]

I know. I screwed up the photos.

[chips]

The third one looks like it is screwed up to the overhead.

[greg w]

New Question for the type 7 experts. On this particular hull the lower bow net cutter "teeth " were removed . How wide should they be and should they be tapered like a knife blade? I know this boat is museum accurate but if I put the part back on
I want it to be as right as possible.Thanks, Greg

[JWLaRue]

Greg,

The teeth are not tapered (i.e.: sharpened). Given that we're talking about the robbe Type VII, I'd make the width of the lower net cutter the same width as that of the upper net cutter so that it looks 'correct.'

-Jeff

[greg w]

Sounds like a good idea to me. Thanks Jeff