SMS Derfflinger 3D Printed Project

Discussion in 'Warship Builds' started by darkapollo, Aug 13, 2021.

  1. darkapollo

    darkapollo Well-Known Member

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    With my love for German ships and knowing that the New Bis is going to take a long time to build and is not a good ship to start out with anyway.. I decided a few months ago (before the old Bis met her demise...) to build a German Battlecruiser to putter around with and get my feet... and knees... and waist... etc wet with an easier to build and arm and something not... 6 units and over 30lbs dry weight.

    It was between the Derf and the VDT. While the VDT has a good reputation for being a good starting ship (at least from the treads Ive read through) there are not too many Derfflingers on the water. They are similar in size, style, and the Derf has an extra 1/2 unit. So I went with the Derfflinger.

    I am really trying to get this in the water for October so this should be a fast moving thread. I have 95% of the things I need, save for multiple battery packs, a new in hydro Co2 tank, and an RC solenoid relay. I have everything to make it at least a floating and driving boat. I also a few canons, motors, prop shafts, etc..

    I should start printing this in PETG this weekend. It is not finalized so I wanted to post this up in case one of the vets sees something I have overlooked.

    Top deck is 3/8"
    The armor belt stringer is 1/8" and extends to 1 rib past end.
    From scale water line down to the hard area 1.25" (scale water line marked on center ribs)
    Ribs are 1/4"
    Rib spacing is 2" on center
    Hard bow is 2"
    Hard stern is 1"

    upload_2021-8-13_11-44-22.png
     
  2. darkapollo

    darkapollo Well-Known Member

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    Just need to figure out how I am chopping it up to print.
    upload_2021-8-15_13-36-29.png
     
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  3. Kotori87

    Kotori87 Well-Known Member

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    Are you planning on printing large sections of the ship at a time, or will you be doing smaller bits (ribs, subdecks, and in-between sections) as separate parts then gluing them together? Are there any designed-in hardware mounts? I think I see motor mounts in there, but is there anything else? Are you planning to print the removable deck pieces, or will those be laser cut/bandsawed/hand-carved/etc from a different material? Any plans for water channeling yet, or will you figure that out later? Just a few questions off the top of my head. I am very impressed with what you've got so far.
     
  4. darkapollo

    darkapollo Well-Known Member

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    I did some math with my slicer and different section sizes. I decided to combine the cap rail with the ribs and impenetrable area and print large chunks at a time. The time difference was negligible between individual pieces and larger combined pieces. Id rather have less joints with only a small increase in print time (plus less goop stringing because PETG..)
    The pieces will be pinned together with ⅛” rod and glued together with estes model cement (Ive tested it on my Bis superstructure printed in the same petg and it forms an extremely strong bond). Since PETG sands like a nice hardwood, I can blend the sections nicely.
    I do have motor mounts and the rudder servo mount built in. That was a huge problem on my Bis and I wanted to eliminate those issues.
    The weather deck is a separate piece to be 3D printed as well. Contemplating picking up woodfill petg. Ive used woodfill pla a lot and it is a joy to use.

    There is basic water channel and I will improve on it before printing those sections. Right now it is just a rectangle cut into the floor. The internal component layout isnt finalized, however as I have it modeled, I feel it will be easy to create parts specific for components during assembly. I am still not set on the canon layout however I should have enough room for everything.
     
  5. darkapollo

    darkapollo Well-Known Member

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    Need some advice on propulsion.
    Right now it is modeled for outboard twin direct drive 550’s on to Vac-U-Boat ⅛” shafts with however big a prop I can fit under her.
    Derf is a 4 screw inline rudder ship but I’m not thinking running 4 props is the best. I have them outboard just due to the angle of the motors for clearance. I have 3 550’s and a single 775 currently available to use.

    I have everything accurately modeled so I can make clearances if need be.
    I would think direct drive on the 550’s would be too much RPM on the shaft, yes?
     
  6. wdodge0912

    wdodge0912 Well-Known Member

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    Doesn't matter
    you can always adjust the end point on the transmitter if you are using an ESC. you could also gear it if you like. I do believe the common setup for a 4 shaft ship is to have the inner 2 shafts powered, while the outer 2 would be stationary and a solid disc to provide drag for slowing the top end and also quickly flipping to reverse.
     
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  7. Bob

    Bob Well-Known Member

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    Derf is best used with two inner props that are 4 blade and 1.5”. You really need to gear the shafts to get the torque needed. Check out Tyler’s build at portpolarbear.com.
     
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  8. bsgkid117

    bsgkid117 Vendor

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    My advice, I'd delete that rudder skeg and use a more square looking rudder. All you're doing is hurting the turning performance of an already not super great turning boat by using the L shaped rudder. Also you don't need to model the smaller forward rudder, I'd delete it and put that extra surface area into the main rudder. Otherwise, great job. If you have any questions about how I do this (3d printed hulls), feel free to PM me.

    Definitely agree with @Bob , geared 550's would be best on this hull. Ive wanted to build a Derf for a long time, have lots of head-plans on how'd I'd set it up.
     
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  9. darkapollo

    darkapollo Well-Known Member

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    I was under the impression that the rules say the forward rudder needs to be there, no? I tried to follow that rudder rules thread but it was… messy.
    If it doesnt need to be there, well alright.

    if I move to inboard I will need to make custom stuffing tubes and shafts and no idea how to do that. There is an old thread on it but the picture links are dead.

    I have 550 gear boxes but no stuffing tubes or motor gears, though I have prop shafts and shaft gears. I can model in a mounting for them.

    Thanks all for the advice. Ive got the third of 9 sections on the printer right now so I have time to get the propulsion end sorted before it is due to be printed.
     
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  10. bsgkid117

    bsgkid117 Vendor

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    Stuffing tubes are "easy" ish.

    Assuming you are running a 1/8" shaft, here is your list of ingredients, per shaft:

    2x https://www.mcmaster.com/6338K562/
    1x https://www.mcmaster.com/8859K172/ cut to length
    1x https://www.mcmaster.com/89535K16/ cut to length

    Send the bushings in with some Loctite 680 retaining compound and they'll never come back out.

    In the past that forward little rudder would have to be there, but we removed that rule some time ago.
     
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  11. darkapollo

    darkapollo Well-Known Member

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    Awesome!
    Ordered those.
    Using the measurements I mocked up the drive motors for inboard and they baarrreeeely fit side by side. So I have to figure out where the stern guns go now.
    Also, a 1.5” prop wont fit under the stern unless I jack up the down angle or carve up the hull for clearance.
    Any ideas on gears?
     
  12. bsgkid117

    bsgkid117 Vendor

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    I normally go to this website for my RC car/rock crawler stuff. I like the Traxxas gears that are $4-8 each, but they're easier to find in 5mm than 1/8 (3.17mm). You could try these: https://www.amainhobbies.com/robins...n-gear-9t-rrp1709/p-qeaxq2yqtzqxactz?v=186486
     
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  13. Kotori87

    Kotori87 Well-Known Member

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    Bigger isn't always better, prop-wise. You also need to consider how they interact with the rest of the ship. For example, I originally had a 1.5" prop on my predread, it was the biggest I could physically fit in the location and was the same size as my rudder height, and placed as close to the rudder as possible. Conventional wisdom states that is the best configuration. However, when I went to a 1.25" prop, I actually ended up with more of my total thrust being redirected by the rudder, so the ship turned much better. YMMV of course, and some experimentation may be required to find the best configuration of blades, pitch, rudders, etc.

    Another consideration, in addition to the prop clearing the hull, is the prop clearing the ground. If you use over-sized props, they tend to stick out underneath the ship. This makes the props more prone to damage from rocks and tree roots and sinking stern-first, and also prevents you from setting your boat flat on a table without a stand. I wouldn't deliberately undersize props to avoid this, but how much your props underhang (for a given size of prop) is something worth thinking about.
     
  14. Bob

    Bob Well-Known Member

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    I run 1.25” on my predreads too. But they weight 12lbs. Derf is in the mid 20s. You need the thrust of a larger prop.

    I’ve always found that copying someone who has already built the ship and done well with it is the best way to built. Copy what Tyler did. He’s had the best built Derf around since he made it.
     
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  15. darkapollo

    darkapollo Well-Known Member

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    New internal motor layout
    upload_2021-8-18_10-1-22.png
    upload_2021-8-18_10-17-47.png
    upload_2021-8-18_10-11-5.png
    1.5" prop just squeezes in with the shafts at a mild 1.5* down angle. Before when I thought they wouldnt fit, I forgot to move the inner shafts rearward (they were in the same place as the outboard shafts) which gave me the clearance to fit the larger prop.
     
    Last edited: Aug 18, 2021
  16. bsgkid117

    bsgkid117 Vendor

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    Dont be afraid to stuff the motors forward in the hull. Your shafts look really short in the pictures, but that could be a misconception based on the pics. You could make the angles much better if the motor mounts were pushed forward in the hull by 4-6" it looks like.

    Most of my ships have shafts that are 11-16" long. Then again, I run SuperBeef(TM) shafts so I'm not concerned with any kind of torque twisting/shaft deflection. Still, try moving the gearbox/mount forward in the hull and see what that opens up for you.
     
  17. darkapollo

    darkapollo Well-Known Member

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    As modeled the shafts are 12" long. (I work better in metric...)
    upload_2021-8-18_11-22-43.png
     
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  18. darkapollo

    darkapollo Well-Known Member

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    Derfflinger has taken over the mobile dry dock. This is the first 3 of (now) 11 sections.
    The next two are on for 49 hours…

    D6320790-33B8-4640-B5B1-24BE3A9294D3.jpeg
     
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  19. bsgkid117

    bsgkid117 Vendor

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    Are you using any sort of physical attachment/alignment aids along with adhesive?

    For alignment/retainment while glue dries, I use m4 bolts and m4 nuts that are modeled into the hulls. The bosses for the nuts capture them to allow easy (ish) assembly.
     
  20. darkapollo

    darkapollo Well-Known Member

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    I have brass rods serving as alignment pins along the cap rail and hard area. The clamps are to force things together since the fitment on the pins is VERY snug.
    After the hull is assembled I am going to sand it and do fiberglass to try and lock everything together.
    PETG is a bear to glue…