Plasma Dart II Build Thread

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

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  1. Jun 13, 2019 #61

    jqavins

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    Joseph Avins

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    Thank figure of speech for spent motors. They have 1001 uses.

    Do you have a plan for the bias cut on the forward end of a new BT5? I may have an idea.
     
  2. Jun 13, 2019 #62

    neil_w

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    Amen to that.

    Um, cut it with a knife? I imagine that with the motor casings supporting it, the cut will be very quick and easy. What did you have in mind?
     
  3. Jun 13, 2019 #63

    jqavins

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    Joseph Avins

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    Stick a motor casing a bit past the end; use masking tape both to fix the tube to the case and to cover the entire length of tube that will be cut; mark the cut on the tape; cut with a razor saw (sacrificing the end of the casing). The saw helps to ensure a straight cut, and covering the tube with tape prevents tear-outs and fuzzies.

    If you're good with a knife cut then go ahead. If it were me, I'd need the sort of help outlined above. I'd even cut a smidgeon outside the line and sand to the line before removing the tape. Because I'm a klutz and need all the guides, aids, and help I can get. See the sig.
     
  4. Jun 13, 2019 #64

    GlenP

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    The forward end mates to the transition, so that is not a pure straight chamfer type cut you would perform with a saw. It would be a curved cut, right? Depends on the relative radius of the transition and tube as to how much curve you have, I guess. A straight cut may be close enough, then you could put sand paper rough side out on the transition and fine tune the fit by sanding to the curve.
     
  5. Jun 13, 2019 #65

    neil_w

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    In theory it seems as if it would not be a straight cut. In practice, the cuts come out pretty straight using my cutting guide. I don't know were the truth lies. To figure it out exactly would require some CAD work.

    However, the question is moot, because I've already made the cuts. The angle cuts up front didn't really come out any better than before, but the straight cuts along the sides and the fins slots are *much* better. I'm going to use the two new pieces and the best of the old ones.
     
  6. Jun 14, 2019 #66

    neil_w

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    Miscellany

    Here's an assortment of stuff.

    1) As suggested by @BABAR (that one's for you Joe), I installed some little reinforcement strips for mounting the warp tubes. As it turned out, I did have enough of my 1/16" square basswood stock to do all six:
    Miscellany-1.jpg
    These hold onto the tube pieces just enough to yield a dry fit that holds together:
    Miscellany-3.jpg
    Miscellany-4.jpg
    As it turns out, that ability was temporary; when i applied CWF to the new warp tube pieces, it expanded them slightly, and now they're no longer as tight. When mounting them, I'll need to squeeze them.

    2) I successfully tweezered an elastic shock cord to the Kevlar loop, working inside the end of the BT55:
    Miscellany-5.jpg
    3) Here's the motor mount, which I built a while ago:
    Miscellany-2.jpg
    The split ring at the end wound up a bit misaligned, as shown in the red circle. "I'll fix that in post."

    The front ring fit really tightly into the body; epoxy was in order for installing this mount.

    Aaaaaand here's the split ring fix: a big glob of Quick and Thick, filling the entire gap (and making a nice strengthening fillet):
    Miscellany-6.jpg
    4) BT55 fits almost perfectly inside the end of a 1" PVC coupler, as long as you don't push it in very far. Makes a good stand for holding my assembly while the motor mount filler glue dries.
    misc bonus.JPG
     
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  7. Jun 14, 2019 #67

    neil_w

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    Things are going to slow down now, as I wait for an opportunity to glue on the warp tubes. I expect it to be a challenging process to get them on correctly.

    In the meantime, I did initial rough-shaping on three little caps to fill in the backs of the warp tubes after assembly is completed. These are 1/16" basswood, somewhat oversized for the moment as I will need to sand each one down to fit at the time of installation.
    warp caps.JPG
    This is probably a good time to start working on the decals some more. Plenty of work there to be done to get them ready for printing.
     
  8. Jun 14, 2019 #68

    BABAR

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    If the tubes swelled with the CWF larger than the basswood guides, will the finish “crack” if you try to constrict them back to the diameter size of the guides?

    For future builds, given these were snug on the basswood guides in post 66, question whether might be reasonable to glue the tubes in place first and then CWF them?
     
  9. Jun 14, 2019 #69

    neil_w

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    Nah, it's totally flexible.

    I think it would be hard to sand them in-place. My real mistake was cutting the pieces before CWF. I was so eager to cut the new pieces that I didn't realize I had forgotten the CWF until afterwards. If CWF first, then cut, should be no problem.
     
  10. Jun 15, 2019 #70

    neil_w

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    Well, that was much ado about nothing. As I was staring at the pieces tonight, it occurred to me to just reshape them back the way they came. I did so be gently and repeatedly squeezing the sides; after a minute of this the pieces had they tighter curve back, and once again grip the rails.

    Mounting them will still require care, but that takes one variable out of the equation.
     
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  11. Jun 15, 2019 #71

    neil_w

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    Mounting the warp tubes

    As mentioned above, making the warp tubes fit properly was simply a matter of gently squeezing them until their curve tightened up. Then they would grip onto the little mounting strips and self-position (well, mostly).

    Unfortunately (?) I couldn't take any picture while gluing them on, because my fingers got gluey and I needed to pay attention to what I was doing. The process was straightforward:
    1) Pull some small TBII fillets on the outside edges of the mounting strips
    2) Apply TBII to the edges of the warp tube piece
    3) Glue into place
    4) Hold for a while, and keep an eye on alignment and positioning all the while

    Alignment was verified by checking the fin mounting lines I had previously put on the body tube. Here you can see that there's proper alignment between the fin line and the fin slot on the warp tube.
    Warp tube mounting-1.jpg
    Here's all three tubes mounted:
    Warp tube mounting-2.jpg
    Quality of the joints varied. Here's my best:
    Warp tube mounting-3.jpg
    That one was *really* good. For comparison, here's my worst:
    Warp tube mounting-4.jpg
    Because of the mounting strips, the tubes felt very solid despite the inconsistent joints around the edges (thanks for that idea @BABAR). The gap, in the meantime, are taken care of with some Quick and Thick:
    Warp tube mounting-5.jpg
    I think that nobody has benefitted more from the Quick and Thick filleting tutorial I wrote than me. I remind myself of the proper steps constantly while I do them. Definitely has improved my success rate.

    I eventually applied two layers of fillets there. Just enough (I hope) to fill the gaps and create a smooth joint. I'm very pleased with the way these came out. I think this was the first time I ever sliced and diced and spliced tubes like this.

    Then it's time to mask the whole thing for filler/primer.
    Warp tube mounting-6.jpg

    Note for the future: precisely masking off the cage attachment points for real painting is going to be miserable. For not I just did it super rough. No primer for now on the warp core itself, not needed.

    I hadn't originally planned to filler/prime this model at all, but since I have a perfect opportunity today I couldn't think of a reason not to. And here we are:
    Warp tube mounting-7.jpg
    Glad to get this done before an extended stretch of wet weather comes in tonight.

    The finish line is in sight, but still more work ahead.
     
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  12. Jun 16, 2019 #72

    BABAR

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    Re: “ Note for the future: precisely masking off the cage attachment points for real painting is going to be miserable.”

    Not sure which way you are masking so I am not certain whether this would help. I have found that in areas where there is a black area that may be hard to get with black paint I have used a black sharpie either before or after gluing to a dark black to the area. You can glue across a sharpie color. As you know, you cannot get good glue fixation across a painted surface.

    Tom
     
  13. Jun 16, 2019 #73

    GlenP

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    FYI - just came across this article:

    http://dart.jhuapl.edu/index.php#page-top

    This spacecraft will use an ion propulsion system to accelerate charged atoms (i.e. PLASMA...the 4th state of matter) So your concept of a plasma dart is really not too far fetched after all.

    "About DART (Double Asteroid Redirection Test)

    NASA's DART mission will be the first ever space mission to demonstrate asteroid deflection by a kinetic impactor. In Fall of 2022, DART is planned to intercept the secondary member of the Didymos system, a binary Near-Earth Asteroid system with characteristics of great interest to NASA's overall planetary defense efforts."

    Sounds like something from Hitchhikers Guide to the Galaxy, at the end of a Disaster Area concert.
     
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  14. Jun 16, 2019 #74

    neil_w

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    Hey man, I am just so *wired in*, I can't even help myself.
     
  15. Jun 17, 2019 #75

    lakeroadster

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    Awesome build thread Neil. That Triple Warp Tube / Body Tube / Transition Section is a work of art.

    Have you ever weighed parts before gluing, then after? I never really thought about it until my Lifting Rocket. The actual as built weights vs Open Rocket weights had me wondering where's the weight difference?

    I had a Capt. Obvious moment, shortly thereafter when I picked up the bottle of TBII... that sucker is heavy.
     
  16. Jun 17, 2019 #76

    neil_w

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    Great question, but I admit I never think of doing it. Like you, I usually just wonder about it afterward.

    When I glue the fins on I'll try to remember to do this.

    True, although much (most?) of it is water weight, which evaporates off. That actually points to an easy experiment: what percentage of the weight of TBII is water? Results to come...
     
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  17. Jun 17, 2019 #77

    jqavins

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    Joseph Avins

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    Hypothesis: the added weight is more from filler and paint than from glue.
     
  18. Jun 17, 2019 #78

    neil_w

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    A quick experiment:

    I started with a piece of 3/32" balsa, approximately the size of a reasonable LPR fin: trapezoidal with a 4" root. Weight: 1.7g.

    I then covered it with TBII:
    Glue weight-1.jpg
    So that's 1.4g of glue. I would estimate this is enough glue for a complete set of fillets, although admittedly it's hard to guess, and depends on how big and heavy you make your fillets.

    After drying:
    Glue weight-2.jpg
    So, 1.4g of wet glue dried down to .7g. So, TBII is *roughly* 50% water. .7g of glue will do quite a bit of fastening or filleting. That's pretty good I think.

    Of course, on complex designs with lots and lots of joints and filleting, those grams will add up. A better, more precise experiment would make some actual fillets, and test the weight per inch of fillet. That's be a useful number. Maybe I'll try that sometime.

    I'm guessing that the weight of glue used to make most bonds (vs. filleting) is darn close to negligible, if you've fitted your surfaces together reasonably.
     
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  19. Jun 17, 2019 #79

    Nytrunner

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    Love the glue weight experiment! When data meets conjecture the world is happy

    "What are you going to do with the new experimental ion drive!?"

    "We're going to crash it into a rock at full speed and see what happens!"
     
  20. Jun 17, 2019 #80

    kuririn

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    Buckaroo Banzai?
    At the end of a recent PBS broadcast (the series name escapes me) a NASA scientist and former astronaut was commenting on ion drive and plasma drive propulsion. He said it could make a round trip to Mars possible in 37 days, rather than 3 years with current technology.
    But somehow I still don't think it can go through a rock. :D
    Tally ho.
     
  21. Jun 17, 2019 #81

    GlenP

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    Cosmic billiards?

    ... Didymos 2 in the corner pocket...
     
  22. Jun 18, 2019 #82

    neil_w

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    Let's weigh some fillets!

    Starting here:
    Fillet weight-1.jpg
    We have a piece of scrap tubing and a 2" piece of balsa. Dry weight: 4.8g.

    Next, we glue them together using TBII:
    Fillet weight-2.JPG
    Still 4.8g, no surprise.

    Next: two nice layers of TBII fillets. End result looks like this:
    fillet weight 4.JPG
    As far as I am concerned, these fillets are as good as I would normally put on a typical low-powered rocket. Final weight:
    Fillet weight-3.jpg
    That's 5.0g for those too lazy to click for the full-sized version.

    And so: a total of 4" of fillet (2" on each side of the fin) came in at .2g (I expected a bit higher TBH). And so .05g per inch of fillet, using TBII. Example: a 4 fin rocket with 4" fin roots => 32" of fillet, or 32 * .05 = 1.6g of fillet.

    It is your choice whether to use this information for good or evil.
     
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  23. Jun 18, 2019 #83

    Nytrunner

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    Throw on a layer of quick and thick and report back?

    (Lol, that's leftover from IRIS prototyping)
     
  24. Jun 18, 2019 #84

    neil_w

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    When I get a chance, I will.

    Darn tootin'.
     
  25. Jun 18, 2019 #85

    jqavins

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    Joseph Avins

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    Fill, sand, prime, sand, and paint, then report back.
     
  26. Jun 18, 2019 #86

    neil_w

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    The Rocket N00b did paint weight tests in the past, and someone around here tested the weight of fillers.

    I will contribute this:

    1. Avery full-sheet label paper weighs 0.08 g/in^2
    2. Medium-density 1/16" balsa weighs 0.18 g/in^2
    3. Medium-density 3/32" balsa weighs 0.27 g/in^2
    4. Medium-density 1/8" balsa weighs 0.36 g/in^2
    Therefore, double-sided label papering nearly doubles the weight of 1/16" fins, adds about 60% to the weight of 3/32" fins, and about 45% to the weight of 1/8" balsa fins.

    That's pretty significant, and why I've added "papered balsa" as a material in my OR installation.
     
    Last edited: Jun 18, 2019
  27. Jun 18, 2019 #87

    Bruiser

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    So how do you add papered balsa as an option in OR? I think that was a contributor to the Defender coming out heavier than expected. Chances are that if I am using balsa for fins, they will be papered. For example, the two stage I am getting ready to start on will have Avery papered 1/8th inch balsa fins.

    BTW, the Plasma Dart is coming along great. Is that electrical tape wrapped around the motor mount tube?

    -Bob
     
  28. Jun 18, 2019 #88

    neil_w

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    You need a new custom material for each fin thickness, although I admit I entered a papered 1/8" balsa and then use it for 3/32" as well because it's pretty close.

    Step 1: Calculate the density for each fin thickness you want to use. In my case, I calculated 1/8" papered balsa to be 0.16 oz/in^3.
    Step 2: Go to Edit->Preferences->Materials. Name your new material something appropriate. I used 'Balsa, 1/8", papered'.
    Step 3: there is no step 3

    The density calculation is pretty straightforward. You can either do a calculation using the number I gave above, or else just make a test piece (say: 3x3"), and then extrapolate to a cubic inch. Make sure for your test piece you're using a balsa weight that is representative of your usage. I usually target something like 11 lb/ft^3. OR's built-in balsa material assumes 10.8 lb/ft^3 by my quick calculation here.

    Yeppers.
     
  29. Jun 20, 2019 #89

    neil_w

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    Filler/primer is now complete. Looking good.
    primer finished.JPG
    Or at least, as good as something can look when it's in the primer stage. (Top section not shown, construction is finished there).

    Weird observation: my shrouds feel softer post-primer. Could the primer have had that effect? both were sealed with CA, although maybe after sanding the CA I didn't have full coverage? Has me rethinking the merits of the @hcmbanjo super-shroud.

    Next up: fins.
     
  30. Jun 20, 2019 #90

    jqavins

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    Somehow it's smaller than I imagined.
     

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