Plasma Dart II Build Thread

Discussion in 'Scratch Built' started by neil_w, May 28, 2019.

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  1. Jun 20, 2019 #91

    lakeroadster

    lakeroadster

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    Thanks for your due diligence Neil. I have come to the conclusion the reason my rockets are so heavy is...

    I am Lakeroadster and I'm a recovering glue-aholic... o_O

    002.JPG
     
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  2. Jun 20, 2019 #92

    jqavins

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    Joseph Avins

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    That looks... like a reasonable hypothesis.
     
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  3. Jun 20, 2019 #93

    neil_w

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    I feel like this was a missed opportunity to say "glue diligence".
     
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  4. Jun 20, 2019 #94

    jqavins

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    You're gaining diverse knowledge, becoming a true glue dilettante.
     
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  5. Jun 21, 2019 #95

    BABAR

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    It is important to stick to your principles
     
  6. Jun 21, 2019 #96

    jqavins

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    Joseph Avins

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    Maybe we should let the thread adhere to Neil's build. We wouldn't want this tangent to hide the real point.
     
  7. Jun 21, 2019 #97

    kuririn

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    Agreed! We are digressing off topic. I haven't a glue what you guys are discussing.:D
     
  8. Jun 21, 2019 #98

    neil_w

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    I don't CA need to stop. When there's a gap between build steps, a tangential discussion is a good way to fillet.

    *mic drop*
     
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  9. Jun 21, 2019 #99

    neil_w

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    Pieces for the warp cage, painted with two coats of Tamiya gloss black. My brushwork just sucks, but I think it'll be OK for these pieces.
    black cage.JPG
    The interior of the ends of the lug are blackened with Sharpie, so as not to cause sticking on the rod.

    Other than the lug piece, these will need a bit of sanding to fit at the last moment before attachment. I made a small mistake by cutting them close before painting. What I should have done is spray-painted one long piece square stock, and then cut to length. I have no way to hold onto these small pieces for spray painting. Even leaving a half-inch extra on one end would have given me something to grab.

    It'll be quite a while before these pieces are used, but I needed to get them done sometime.
     
  10. Jun 21, 2019 #100

    jqavins

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    Does the present tense "have no way to hold..." imply that you still have painting to do? Or have you finished them with the brush work?

    If you still need to spray, try this: shove the smallest nail you can find, or even just a piece of thin wire in on an end, leaving a little sticking out. Use that to hang the piece by a string or wire and spray. Or even attach the string with a tiny dab of chewing gum. (OK, Fun-Tak or equivalent.) Point is, don't try to "hold" the pieces, but rather hang them by an end.
     
  11. Jun 22, 2019 #101

    BABAR

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    I think there is a section in Hitchiker’s Guide to the Galaxy that says you should change out your warp core cages every 25 bazillion light years, so I think the brush strokes make it look appropriately broken in. So Don’t Panic!
     
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  12. Jun 22, 2019 #102

    neil_w

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    Yes, I've finished with the brushwork. Your suggestion would absolutely work, however I think that if I try to improve on these pieces I'll just make new ones. Spray a whole stick (easy), and then cut into pieces. Literally cannot imagine why I didn't think of doing it that way in the first place.

    I've never tried the pins-in-the-end method for holding things; I know it can be used to hold fins as well. I just never think of it at the time.
     
  13. Jun 22, 2019 #103

    BABAR

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    Thinking outside the square box, seems like a cage should have bars, rather than plates.

    Would dowels or wooden skewers work?
     
  14. Jun 24, 2019 #104

    neil_w

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    Almost anything would work for the five that do not support the launch lug. I consider a zillion things and settled on square dowels because... well I don't actually remember anymore. Round would have worked (again, for 5 out of the 6).

    However, at this point I'm pretty committed to square. I decided to blow $0.75 on a new piece of bass square dowel and repaint with rattle can (paint first, then cut). The launch lug will stay as is, but I'll replace the other five.

    Here is the most exciting build photo ever:
    newstock.JPG
     
  15. Jun 24, 2019 #105

    jqavins

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    Joseph Avins

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    Be careful. That sort of reckless spending can catch up with you, y'know.
     
  16. Jun 24, 2019 #106

    neil_w

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  17. Jun 26, 2019 #107

    neil_w

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    I've been doing some decal work. It's been a bit of challenge I must say.

    The cockpit decal in OR is distorted by being projected onto a conical transition. Therefore I needed to figure out the "real" shape to print the decal. The math to do this analytically is beyond me, so I had to do some "real world" testing.

    I make a quickie cardstock transition to match the balsa transition in the model, attached it to a piece of scrap tube, and then iteratively worked the shape of the cockpit decal in Paint.net until it matched the OR rendering, as close as I could get it. It took me *many* tried before I finally got it right. The shape ended up significantly different from the decal image used in OR:
    upload_2019-6-26_17-21-15.png

    Here's the final mockup (this should give Nytrunner another chuckle):
    decal test.JPG

    The fin decals are another project I haven't tackled yet.
     
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  18. Jun 27, 2019 #108

    GlenP

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    I had similar challenges in making these cardstock models with the window decals on the nose cones, reproductions of the Estes Starliner and Star Seeker (from the mini Tri Pak) I usually end up making a couple of iterations by trial and error to get the seams to line up right.

    DSC_7405.jpg
     
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  19. Jun 27, 2019 #109

    jqavins

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    It's not beyond me, and I'm here to tell you it would be a giant PITA. And when it's finished you'd still have to use the resulting equation to construct the decal. Your way is better.
     
  20. Jun 27, 2019 #110

    neil_w

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    No matter how much time I spend here I still keep discovering Estes kits that I was previously unaware of, in this case the Starliner. Very nice, I am always impressed by your cardstock models. Do you have a picture of your whole fleet?

    Regarding this decal, it now occurs to me that what I should have done (or maybe still should do) is superimpose the cockpit decal on the shroud template; that would give me some additional clarity about lining up angles and things.
     
  21. Jun 27, 2019 #111

    neil_w

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    I'm starting to get an idea about what I could do analytically, in conjunction with the transition shroud. I would not generate the entire decal in code, but I could create some alignment marks and use them as guides for my drawing. I just might still try that, to provide final tweaking to my image. Will see if I have time before I print the decals (of course I *do* have time, since it'll be a while yet before we get to decals.)
     
  22. Jun 27, 2019 #112

    neil_w

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    Fins

    Time to make the fins! Actually I made them a while ago, so maybe I should say: Time to show how I made the fins! Here is *far* too long of a post about a set of three LPR fins. You have been warned.

    As with many other parts of this design, I dithered endlessly over the fin shape and wasn't (and still am not) sure if I made the right choice in the end. They were a bit harder to fabricate than I expected, especially since my first impression was that this was going to be the easiest set of fins I've made in a while. Not so!

    Here's the target shape:
    upload_2019-6-27_10-0-11.png
    Trying to figure out grain direction and how to incorporate the spike were the sticking points here. My first attempt was simple: one piece, with the antenna glued underneath the overhang:
    upload_2019-6-27_10-1-42.png
    I used 1/8" dowel for the spike. Here's the result:
    fins-1.jpg

    There was too little anchoring for the dowel, and basically no support (other than the label paper) for the overhang (it felt a bit flexy for me). Also I found the 1/8" dowel to be too thick-looking. So I moved onto version 2: two pieces, with a smaller dowel. I re-jiggered the top part of the fin to address the weakness of the previous version:
    upload_2019-6-27_10-7-10.png
    I sanded down my 1/8" dowel down to 3/32" to match the fin thickness.

    Here's a hint for anyone considering thinning out hardwood dowel by sanding it: run the other way. Think of an alternative. Even taking 1/32" of thickness off about 6" of dowel was extremely tedious and it was very hard to make it consistent and even. Ugh. I did eventually come up with a satisfactory result, but I won't be doing that again any time soon.

    Now I was a little worried about the weakness of the top piece, but hoped it was small enough that it wouldn't be an issue. It looked good...
    fins-2.jpg
    ...for a while at least
    fins-3.jpg
    Sure enough, the top piece broke along the grain (you can't tell from the picture but the break is *in* the top piece, not the glue joint, which held). Here I had decided that perhaps I should CWF these fins instead of papering, and this mishap happened while sanding. It's possible that had I papered the fins it would have provided sufficient additional strength to the top part, but I wasn't interested in finding out. So I created version 3:
    upload_2019-6-27_10-13-6.png

    It's basically the same as #1, but I added a notch into the top so that the spike would be better anchored, and therefore able to provide some support to the overhang. This, finally, was what I went with. Honestly, I'm not sure how much better it is than #1, but it felt a bit better and *I* felt a bit better about it. And the thinner antenna was *definitely* better.

    I applied CWF to fill in the notch, and then papered over the whole thing. I thought it would be very hard to work around the antenna but it wasn't so bad. I did have to cut some weird pieces of label paper:
    upload_2019-6-27_10-19-27.png
    While sanding the filler/primer, I foolishly held a fin by the corner (lower left in the image above), an obvious weak spot that is strengthened only somewhat by the label paper, and this happened:
    upload_2019-6-27_10-21-59.png
    @BABAR often warns how label paper does not add sufficient strength to compensate for bad grain direction: I figured I'd provide a live demonstration of that. :rolleyes:

    Fortunately, I was able to glue the piece back in between the label paper, and then I CAed the paper down. In the end, it's invisible, and that corner will be glued down to body tube so there will be no strength issue.

    And so we (finally!) have a finished set of fins:
    upload_2019-6-27_10-24-46.png

    One last note: I made the fin tabs taller than necessary, so I could sand to fit as needed. What I *didn't* do was take care to make sure the tab edges were straight. That was stupid, because now I need to change the angle of the root as I sand them, which is a heck of a lot harder to do accurately than just shortening them down. *sigh*
     
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  23. Jun 27, 2019 #113

    jqavins

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    Question: Does papering with glue add enough strength to forget about grain dieection? I know it adds strength to help with grain issues, but is it enough to just not even think about them?
     
    Last edited: Jun 27, 2019
  24. Jun 27, 2019 #114

    mbeels

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    I'm curious as well. I keep thinking about doing some testing with plywood and papered balsa fins, but haven't yet taken the initiative to do so.
     
  25. Jun 27, 2019 #115

    neil_w

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    Don't know. I would guess that in marginal situations like mine, it might be enough to avoid worry. Whether you can take it all the way and completely ignore grain.... well, I await someone's tests before I would go there.

    I need to experiment with glue papering one of these days and see what it's like. I like the instant gratification of label papering, but the idea of pre-papering a sheet with glued copy paper sounds very appealing, along with the added strength. I need to see what it's like to try rounding edges and that sort of thing.
     
  26. Jun 27, 2019 #116

    BABAR

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    No. I speak from experience.
     
  27. Jun 27, 2019 #117

    BABAR

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    no, glued paper does NOT make up for wrong grain direction. This is why I drone on and on about marking the grain direction on your paper to make sure you are keeping track of it.

    If you have a structure that requires material strength in two different axes (example is a rotor stop on a helicopter rocket, or a fin that has multiple curves or corners that like to break off) and you want to keep it relatively light weight, you can create a two ply balsa, identical shaped parts with balsa grain in orthogonal directions (90 degrees opposed.) I usually use 1/16" pieces for a final 1/8" product.

    Fix them with wood glue, enough for complete coverage but squeegeed out so good contact. Wrap in waxed paper and stick them in an old book or something with weight on them to keep them absolutely flat, otherwise they WILL warp.

    You can add glued on paper if you want even MORE strength and/or you just hate using CWF or other fillers to get a good surface prep.
     
    Last edited: Jun 27, 2019
  28. Jun 27, 2019 #118

    GlenP

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    If you “paper” them with another layer of wood with variable grain direction, but that’s plywood I guess...
     
  29. Jun 27, 2019 #119

    neil_w

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    I wonder how well this would work as a general-purpose fin material. Could make a big batch of it, and then no more worries about multi-piece fins, or orientation of fins on the sheet, or anything.

    I would tend to think it wouldn't be as strong in all directions as a single piece of balsa against the grain, but maybe good enough for typical LPR?
     
  30. Jun 27, 2019 #120

    kuririn

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    I would think that the opposing grain direction combined with the adhesive would make balsa plywood stronger. Just a feeling, no scientific data to support this. And the idea of cutting something without paying attention to grain layout is appealing.
     

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