Plasma Dart II Build Thread

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

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  1. May 28, 2019 #1

    neil_w

    neil_w

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    I've been holding off starting this one, but now seems to be the time. Let's kick it off with this, which was a jolly good bit of fun to make:
    pdii_facecard2.png
     
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  2. May 28, 2019 #2

    neil_w

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    And here's a more proper overview of the design:
    Overview.png

    Some notes:

    1) Those paying attention may notice that a number of changes have been made since last I fussed over it over in my half-baked design thread. I had more trouble finalizing this design than any other I've worked on thus far, and can't say for I'm totally satisfied with it even now. But I'm happy enough to move forward with it. Huge thanks go out to @Nytrunner and @jqavins for their help in getting me to this point.

    2) I originally intended this to have a 24mm mount, but I became frustrated with the retention issues (don't like friction fit) and so downgraded to 18mm. Due to the dragginess of the design, OR doesn't seem to think it'll go very high, even on a Questjet D16. I've got an altimeter bay up front, so we'll see. I think OR is being a bit pessimistic here. Still, this thing isn't going to win any altitude competitions.

    3) I made this rocket one click too small. One size bigger would have made a 24mm mount straightforward, and also some of the bits of fabrication would have been a lot easier. Unfortunately I realized this too late to change.

    4) In contrast to all my other builds, I'm doing massive amounts of parts preparation before actually putting stuff together. We'll see how it goes.
     
    Last edited: May 28, 2019
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  3. May 28, 2019 #3

    Nytrunner

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  4. May 28, 2019 #4

    neil_w

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    In the first picture I configured each of the three warp tubes as a motor mount, just to get a better looking flame. :)

    Sadly, though, they can't fit motors as the rocket is currently configured. One click larger with a 24mm mount would have been perfect, and then I probably could have fit 13mm motors in the warp tubes.

    As it is for the moment, it is irreversibly a single-motor model. I could still change my mind at the last minute and go with a 24mm mount but I'm not inclined to at this point.
     
  5. May 28, 2019 #5

    Tobor

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    Awesome graphic/face card and wicked cool design.

    Subscribed.
     
  6. May 28, 2019 #6

    BABAR

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    Mucho coolo!
     
  7. May 28, 2019 #7

    Ted Curtis

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    Very cool looking rocket! Would be fun to see it upscaled to 2.6, 3 " diameter.
     
  8. May 28, 2019 #8

    JonathanOtt

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  9. May 28, 2019 #9

    mbeels

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    Very nice, it is interesting how that black band with the blue circles gives the impression that there is a contoured window shape there for the cockpit, but I see it is a cleverly painted transition. Nice effect. And the "plasma chamber" looks pretty cool, this will be interesting to see take shape. Well proportioned, I really like this one!
     
  10. May 28, 2019 #10

    neil_w

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    I fixed the overview image in the second posting, which had some inexcusable decal errors on the fins.
     
  11. May 28, 2019 #11

    Nytrunner

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    Are you sure? I still don't see plasma :eek:
     
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  12. May 28, 2019 #12

    neil_w

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    Transition shrouds

    I started by preparing the two transitions for either side of the warp core. The one in front is a completely straightforward 1", BT60 -> BT55.
    forward transition.JPG

    The one in the rear is a little more interesting: it's 1", BT60 -> BT50H, but it'll have the three BT5 warp tubes intersecting it. At first I thought about cutting the tubes square and making cutouts in the transition, but decided that would be way too hard, since there'd be almost nothing left of the transition and it wouldn't hold any shape. So instead I planned to cut the warp tubes to fit the transition. I used a script I had created previously for the APRO Lander II to generate the appropriate template, which looks like this:
    upload_2019-5-28_16-56-25.png

    The red oval-y bits show where the warp tubes will mate up. Note that one of the tubes will cover the seam in the shroud, so the seam will be hidden. Finished shroud looks like this:
    aft transition.JPG

    We'll see how accurate those outlines are when we cut the warp tubes.

    I'm getting pretty good at making these, each of these was my first attempt and came out pretty much perfect. That's 65 lb cardstock; I haven't found the need to make them heavier if the shroud is not in harm's way. I might coat the forward shroud with CA, but not the aft shroud, since I'll be attempting to glue body tubes to it.
     
  13. May 29, 2019 #13

    neil_w

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    Warp Core Centering Rings

    The warp core is bookended by two plywood centering rings, each one of which will anchor a transition. The 6 pieces of basswood square dowel (what I call the "warp cage") that surround the core will be added at the very end of the build, because the interior will need painting and decals first. I expect this to be a pain, but that's in the future.

    I made a template to help me keep track of where the cage pieces would go:
    upload_2019-5-29_7-58-7.png
    Then I used that to transfer markings to the rings:
    Core-rings-1.jpg

    In addition to showing where the cage pieces will go, the markings on the inside edge will help me align the two rings with each other.

    The launch lug will be mounted to one of the cage pieces. I debated this more than any other part of the design (considered every possible option, I assure you), and I'm still not certain about it, but it's what I'm going with. First I glued the lug to one of the pieces:
    lug.JPG

    It's overly long for now; I'll trim it to size at the end. The lug is *very* securely glued, the piece is quite strong. Eventually it will be glued between the two centering rings. I thought a surface gluing would not be enough, so I build a small "pocket" onto each ring to provide a stronger mount:
    Core-rings-2.jpg

    Will that be strong enough to hold the lug? Won't know for sure until the launch button is pressed.

    I beveled the outer edge of each ring so it would fit comfortably into the end of one of the transitions (this is dry fit only):
    rings finished.JPG

    I darkened the markings on the rings and applied a layer of thinned CWF to the rings, and sanded.
    Core-rings-3.jpg

    And that is more than should ever be written about two centering rings.
     
  14. May 30, 2019 #14

    neil_w

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    Warp Tubes: warning long post

    The three warp tubes in the back are a pain, for one main reason: BT5. Cutting these tubes were the moment where I realized I should have made the whole model bigger, because doing complex cuts on BT5 tubes is awful. Not because they're small, but because they're *flimsy*. In the past I purchased a set of couplers in every tube size to support tubes when cutting them... or shall I say every tube size *except* BT5. And now, as I write this, I realize that I could have simply used some spent 13mm motors to serve as supports while I cut. Quel idiot. If I had enough BT5 left over I would consider cutting them all again, but I don't, so I'm gonna just live with what I have.

    Anyway.

    I coated the tubes first with very thin CWF. Here it is before sanding (forgive the fuzzy picture):
    spirals.JPG

    I am loving this approach, and plan to use it whenever the tubes aren't too big. Much easier than trying to contain the filler within the spirals, and has the benefit of smoothing out all irregularities in the tube, not just the spirals. Sands very quickly. This picture also shows how small these damned tubes are.

    Figuring out the exact cuts took some work. I wrote a new script to generate my cutting template, shown below. The red line is the one I actually need to cut:
    upload_2019-5-30_9-8-20.png

    It's similar but not quite the same as a diagonal cut, because the cut end will be joining a conical transition. There will also be a fin slot cut along the fin line (because these pieces are far too flimsy to serve as mounts for the fins). I'll measure those in by hand.

    Getting this wrapped onto the tube exactly straight was tricky. I made a straight line on the tube first, so I could make sure the fin line was properly aligned front and back:
    Warpmotors-4.jpg

    And here's the tube, marked up and ready for cutting (I've added the fin slot markings):
    Warpmotors-5.jpg

    Nothin' to do now but start cutting. For once I was sure to start with a fresh blade. These tubes cut through very quickly, which is not always a good thing when you're trying to go very slowly and accurately. Surprisingly, making the straight cuts along the length of the tube was the most difficult, again because of the flimsiness of the tubing. I kept trying to fashion some sort of jig, but everything I tried was too big. Finally I went and purchased a piece of square brass stock at Ace (was fun looking through the whole store trying to find a suitable item) and came up with this cheesy setup for doing my longitudinal cuts:
    Warpmotors-8.jpg

    Definitely worked better than doing it freehand; I actually threw away my first piece, because the long cuts came out too crooked (which is what caused me to put together this "jig").

    Again, putting some 13mm motors in there to support the tube would have completely solved this problem. :mad:

    After cutting one piece but before cutting the fin slots, I tested fit against the transition to see if my cutting template was actually correct:
    Warpmotors-2.jpg
    Warpmotors-3.jpg

    Pretty good I'd say!

    There was a bit of challenge cutting the fin slots but I'll spare you those details. Here are the three finished pieces:
    Warpmotors-9.jpg

    The edges are all a bit ragged despite my best efforts to sand them smooth. All edges were coated with a bit of TBII; no CA here because they'll be glued to other paper later. No doubt a good bit of filleting and maybe even some CWF will be needed eventually to join these smoothly to the rocket.

    Finishing these pieces was a relief. Fancy tube cuts are not my forte, because I just haven't done them very often. I didn't measure total time to make these, but if you include writing the script, figuring out how to jig the cuts, etc., it was more than I would care to admit to.
     
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  15. May 30, 2019 #15

    Nytrunner

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    Love the iteration and experimentation.

    Your attention to detail is what makes your designs/builds amazing
     
  16. May 30, 2019 #16

    GlenP

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    Are you going to chamfer trim the aft end of the side tubes at an angle to be even with the trailing edge of the fins?

    To make the fit more exact on the front end you can tape some sandpaper to the transition and use that as a sanding blocks to smooth up the chamfer cuts. but already looks like you got it spot on.
     
  17. May 30, 2019 #17

    Gary Byrum

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    Now you got me. If it were mine, I'd coat the inside of the tubes with CA. This is no threat to the outside surface. Both shrouds would have been treated all over prior to any cutting as it makes both tube edges and slots way more manageable / sandable. And you won't have fuzzy edges when you sand them.
     
  18. May 30, 2019 #18

    neil_w

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    No, was planning to keep them square. Not sure which way would look better, so I took the simpler route. :)

    That probably would have been helpful. I could still do it just to stiffen them up a bit, although once mounted with the fins going through them they should be adequately supported.

    The shrouds aren't being cut, just the tubes. I am expecting that the fuzzy edges will be adequately covered by fillets in the end. All of the edges that will be exposed are clean, and will be CA-coated.

    If I had some more BT5 handy I'd do some more experimentation (including internal coating with CA) to see if I could improve the cleanliness of my cuts. But for now I'm gonna have to live with these.
     
  19. May 31, 2019 #19

    neil_w

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    Fin Jig

    While experimenting with dry-fitting all the warp tubes, I found that it was quite difficult to hold them steady and/or straight. So I thought I'd have a go at making a foamboard fin jig. This will be only the second time I've used one of these; had mixed results the first time but I think I understand a bit better what they can and can't do this time. On the other hand, that one was easier to make.

    Here's the template I came up with:
    upload_2019-5-31_9-3-39.png
    I need to cut out all the solid parts. Will the remaining foamboard have enough structure to be useful? We'll see.

    First I cut out the center hold for the main BT50H. Got a decent fit. Cutting the tight curve is a pain, compared to the super-easy straight cuts for the fin slots.
    Finguide-2.jpg
    Next, the cuts for the warp tubes. If cutting curves for a BT50 is hard, then cutting BT5-sized curves is... harder. I did "OK", and fit was decent:
    Finguide-3.jpg
    I then went and cut the fin slots, that was uneventful. I was not happy, though, that after making the cuts for the warp tubes, and the little bevels to keep the guide out of the glue joints, there was very little holding the center tube in place. After a while I decided that I could firm it up those very small contact areas with some blue tape. That worked OK, and so the finished guide looks like this:
    Finguide-4.jpg

    I think/hope this will work, at least well enough to justify itself.
     
  20. May 31, 2019 #20

    jqavins

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    What about attaching the fins to the the warp tubes first, then using the jig you just made to align those subassemblies around the main tube?
     
  21. May 31, 2019 #21

    neil_w

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    It's hard to convey without actually holding the parts in your hands, but I'm pretty sure that won't work. What I do plan to do, though, is to dry-fit the fins in place while gluing the warp tubes, so I am hoping to get *some* of the benefit of what you're suggesting. That's going to be an adventure, I'm sure.

    In the meantime, just fabricating these damned fins is turning out to be a horrible mess, and I thought they were going to be a quick and easy part of the build. Ha!
     
  22. May 31, 2019 #22

    Nytrunner

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    You really move fast once you've got things started
     
  23. Jun 1, 2019 #23

    neil_w

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    I am pleased that I have hoodwinked you into believing that. ;)

    In fact I started this build many weeks ago. Nowadays I delay my build threads until I have a good queue of postings ready to go at the start. Eventually I'll catch up with myself and then the build thread will come screeching to a halt. Like when painting time comes....
     
  24. Jun 1, 2019 #24

    lakeroadster

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    Nothing wrong with fuzzy edges... that's more surface area for the wood glue..... and coating tubes with CA means when you use wood glue it won't be able to penetrate into the wood fibers.

    Save the CA until after the wood glue is finished doing it's thang.

    Awesome thread Neil, really enjoying this.
     
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  25. Jun 1, 2019 #25

    BABAR

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    Suggestion for both alignment and ease and strength of your body tube to body tube attachments.

    On your main/core/central tubes mark the attachment lines for your BT5s. Get some 1/16” balsa, cut 1/16” wide lengths (I guess you could call them strakes). Glue these in place just inside your marker lines for the BT5 attachments. Because they are small and light, they will attach easily.

    Then when you go to attach your BT5s, they will line up in exactly the right place, and the strakes provide a larger surface area for bonding.
     
  26. Jun 1, 2019 #26

    neil_w

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    Hmm, might just try that if I can be confident of positioning the pieces correctly.
     
  27. Jun 2, 2019 #27

    jqavins

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    You can get 1/16 square stock at the better hobby shops.
     
  28. Jun 2, 2019 #28

    neil_w

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    That's what I used for the little pockets on the centering rings. Probably don't have enough on-hand for the suggested use, though.
     
  29. Jun 2, 2019 #29

    BABAR

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    True, but for this purpose why bother? Assuming the BT5s are 6” long, easy enough to take a 6” piece of 1/16” balsa and cut 6 strips (2 for each BT5) each 1/16” wide (you can be off as much as another 1/8”, all that matters is that on each strip at least ONE side is perfectly straight.) line the straight edge of the balsa along the INSIDE edge of your marker lines

    You could use 1/8” balsa as well, a tough more weight but likely negligible for a sport model, and would provide a stronger bond.

    I often use the 1/16 strips as “cheaters” to help line up my fins on regular rockets, they are small enough that you can just about hide them in the fillet.
     
  30. Jun 2, 2019 #30

    GlenP

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    is the rocket itself the dart, or is the rocket a vehicle used to expel a "dart" of plasma from its nose? ... something to consider ...

    you could cut off the black tip portion of the nose, turn it around and insert it into the open nose cone. Paint the inside of this "nozzle" metallic so it looks like a conduit from which the dart of plasma is expelled... if that makes any sense. The icon picture you made for your avatar has this optical illusion that the tip of the cone has been truncated, and I think looks really cool and is consistent with the plasma dart theme, although not very aerodynamic. The blue trim around the nose kind of looks like the blue plasma burn marks from when the dart was fired, you know?

    just an idea. Will turn out totally awesome as usual, no matter how you decide to finish it, another great addition to your fleet.
     
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