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    1:72 U boot Scratch built

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    JuanGg

    Posts : 8
    Join date : 2017-05-03
    Location : Spain

    1:72 U boot Scratch built Empty 1:72 U boot Scratch built

    Post  JuanGg on Fri May 05, 2017 9:00 pm

    Hello, my name is Juan and I am from Spain.

    I am new to this forum and I am going to describe a project that I started two years ago and needs some modifications to be done for it to work properly. I would be proud to hear sugestions!

    Sorry for any mistakes made using English language.

    The main objectives were:

    -Low cost : For now it is below 240 € without radio equipment (+- 150 €)
    -Simple hull, made out of wood (later discovered that this was not the best material for underwater stuff!)
    -Static diving
    -At least one hour of battery.
    -Operating foward dive planes and twin ruders (only four chanels, so no rear planes).
    -Similar to an Type IXB german U Boot.

    First stages from the build, as you can see, simple , square-shaped hull:

    1:72 U boot Scratch built P1060616
    1:72 U boot Scratch built P1060617
    Water tight compartment.

    1:72 U boot Scratch built P1060619
    Policarbonate sheet cut and drilled to form the acess hatch.

    1:72 U boot Scratch built P1060623
    Hull construction, simple shapes, cheap and "easy".

    1:72 U boot Scratch built P1060622
    Fore.


    1:72 U boot Scratch built P1060620
    Aft.


    After foward and rear planes had been fitted, rudder assembly done, and frther hull work it looked like this:

    1:72 U boot Scratch built P1060610
    1:72 U boot Scratch built P1060612
    1:72 U boot Scratch built P1060611
    1:72 U boot Scratch built P1060613


    Dive planes and rudders were made out of a zinc sheet, bent and soldered. Pushrods are 2mm brass rods, sealed with rubber bellows.
    Motors used were taken from an old printer and fixed using a 3d printed piece. Another 3d printed piece is used to hold the propeller shafts. Everithing is glued in place with 30 min epoxy.

    Next comes the big mistake of this submarine: The ballast tank: (Quite a strange shape!)
    1:72 U boot Scratch built P1060615
    1:72 U boot Scratch built P1060614
    1:72 U boot Scratch built P1060710
    The model you can see on the background of the last photo is a static model I took as a reference.

    Made out of 1 mm iron sheet, bent and soldered into shape, and then painted from the outside and from the inside filling it with paint and then removing it to prevent corrosion; It proved too long for the task, its never filled completely and water moves very fast inside it with nothing preventing that, making the submarine incontrollable when submerged. (More on that later, posible solutions, etc) Total volume of the tank is nearly 750 ml.
    As a surface boat, performs well, but at the moment controlled diving is nearly imposible.

    Unaware of the problems it will cause, the ballast tank was fixed to the hull with lots of silicone:

    1:72 U boot Scratch built P1060711

    The hull was nearly completed and painted with a primer:

    1:72 U boot Scratch built P1060715
    1:72 U boot Scratch built P1060714
    1:72 U boot Scratch built P1060712
    1:72 U boot Scratch built P1060713

    Ballast system: Windscreen water pump, servo operated three way valve,

    1:72 U boot Scratch built P1060717
    1:72 U boot Scratch built Http<a href=
    1:72 U boot Scratch built P1060718
    1:72 U boot Scratch built P1060722

    Then the policarbonate sheet was cut to shape, drilled, fitted with screws and glued to the wtc:

    1:72 U boot Scratch built P1060720
    1:72 U boot Scratch built P1060719

    The gasket was made out of soft silicone after trying numerous materials.

    Then, two wood stripes were glued onto the sides of the sub.

    1:72 U boot Scratch built P1060721

    All the wood parts were coated with epoxy paint:

    1:72 U boot Scratch built Captur10



    Then, the deck, sail, guns etc. were designed in FreeCAD:

    1:72 U boot Scratch built Freeca12
    1:72 U boot Scratch built Freeca13
    1:72 U boot Scratch built Freeca10
    1:72 U boot Scratch built Freeca11

    And then 3d printed using white abs, glued with acetone and fitted to the hull:

    1:72 U boot Scratch built Captur10
    1:72 U boot Scratch built Captur11
    1:72 U boot Scratch built Captur11
    That black thing on the photo is the fuse cover. The fuse is used to switch on an off the entire submarine.

    1:72 U boot Scratch built Img_5110

    After all comes the painting job :

    1:72 U boot Scratch built P1060812
    1:72 U boot Scratch built P1060910
    1:72 U boot Scratch built P1060911

    And the final result:

    1:72 U boot Scratch built Captur13
    1:72 U boot Scratch built Captur12

    First trials in the swiming pool:

    1:72 U boot Scratch built Captur12

    And in the local pond:

    1:72 U boot Scratch built P1070010

    Result:

    > Speed: A bit faster than scale.

    > Turning: Fine. Small turning circle. Rudders work great.

    > Diving: It dives, but it can't return to surface. After filling the tank, it goes vertical and any try to emerge causes compresed air to release and sinking the sub to the botom.

    > Foward dive planes : Useless, even at 45 degrees seem to have no effect.

    > Watertightness: Not leaked a single drop.

    > Batteries: One 1300 mA 11.1 v Lithium battery lasts about 45 mins-1 h


    Ballast system explanation & posible solution:

    > Here is the schematic of the ballast system: A  "water sealed tank" or a "high presure pump" system:

    1:72 U boot Scratch built Ballas10

    To dive, a servo opens the valve and presses a microswitch that activates a windscreeen pump, wich pushes water into the tank, compresing the air inside. Then , the valve is closed.
    To emerge, simply open the valve and air presure will force the water out.

    There comes the problems I have encountered:

    1st: In a long tank, water moves back and foward very quickly, making the sub very inestable.
    2nd: In certain situations, air can escape when openning the valve, loosing poresure and beeing unable to surface again.

    Case A: Center of gravity (CG) foward, imposible to dive in a controlled manner, but able to surface.

    1:72 U boot Scratch built Ballas13

    Case B: CG back, imposible to dive in a controlled manner, unable to surface, if the valve is opened, compresed air will escape before water. You have to get wet.

    1:72 U boot Scratch built Ballas14

    Posible solution:
    As I do not need all the volume of the tank, sides of it can be sacrificed to shorten it, thus making it more stable.
    Furthermore, adding a kind of bulkheads inside will unable air to scape in any position (not turning the sub over) and willl certainly make the sub far more stable.
    See the images:
    1:72 U boot Scratch built Ballas11
    1:72 U boot Scratch built Ballas16

    Now, how to put those bulkheads inside a 1 mm wall stell tank? The tank itself is the botom of the sub, s you can see in the photos, so the only way to do it is to cut it open, add the bulkheads, fill sides with silicone and close it again !


    Last edited by JuanGg on Sun May 14, 2017 7:30 pm; edited 2 times in total
    david f
    david f
    AMS Treasurer

    Posts : 2039
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    Age : 69
    Location : Cumbria

    1:72 U boot Scratch built Empty Re: 1:72 U boot Scratch built

    Post  david f on Tue May 09, 2017 5:48 pm

    Ola Juan !  (And I must compliment you on your English.)

    Also a fascinating description of your sub build. It makes a really good model and I was most impressed by the 3D printing you used.

    Sorry you have hit problems with the pressure tank ballast system.  It can be problematic:

    - it needs baffles for most tanks (longitudinal stability was also a problem for the original full size sub builders e.g Garratt)

    - design of the tank to resist pressure can be a problem (cylindrical tanks are easier.)

    - when the sub tilts you can lose your air bubble with disastrous results. Keep the inlet/outlet pipe low down in the centre of the tank.

    Have a read of this link for some discussion of problems and some people's solutions.

    http://www.theassociationofmodelsubmariners.com/t1418-pressure-tank-ballast-system-ballast-tank?highlight=ballast
    avatar
    JuanGg

    Posts : 8
    Join date : 2017-05-03
    Location : Spain

    1:72 U boot Scratch built Empty Re: 1:72 U boot Scratch built

    Post  JuanGg on Sun May 14, 2017 6:57 pm

    Thank you for the early response,
    I know that cilindrical tanks are far more easy to build and stronger too. The thing is that this model has a square shaped wtc, and in order to get the maximun tank capacity (only fills to 3/4 and at that moment I did not know how was the deck going to be made) I had to make it square and with aditional space under the wtc. Thank you again for the link, really interesting information.

    In fact, I have already cut a hole in the ballast tank to put the bulkheads in, see the photos:

    1:72 U boot Scratch built P1070110
    Hole shape marked. Had to go through 6-8 layers of paint to reach the metal.

    1:72 U boot Scratch built P1070112
    After cutting it. Notice the existing bafles, wich were there to prevent the tank from deforming under presure, but do not prevent water to move around.

    1:72 U boot Scratch built P1070111
    The inside, closer. You can see steel powder from the cut.

    Everything was painted with minium /red lead paint. Had been 2 years closed, not smelling good. Paint was removed using a metal brush, with a mask as I don´t think swallowing minium powder is good for health.


    Paint almost completely removed and 3d printed bulkheads trimed to fit:

    1:72 U boot Scratch built P1070115
    Now we have four independent compartments.

    1:72 U boot Scratch built P1070113

    1:72 U boot Scratch built P1070114

    The bulkheads will be epoxy glued to the inside of the tank, and then everything will be painted.

    Hole will be closed gluing another steel sheet to the underside of the tank. I am not really sure if epoxy will cope well with 4 atm, but I prefer that to welding, as I don't want to heat everything up. Lets see how it goes.
    avatar
    JuanGg

    Posts : 8
    Join date : 2017-05-03
    Location : Spain

    1:72 U boot Scratch built Empty Re: 1:72 U boot Scratch built

    Post  JuanGg on Sun May 14, 2017 7:33 pm

    Found some photos of the very early stages of the model, and added them.

      Current date/time is Sun Aug 18, 2019 6:25 am