New 102mm project - Chimichunga-I

Discussion in 'High Power Rocketry (HPR)' started by snrkl, Mar 20, 2018.

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  1. Sep 11, 2018 #211

    jlabrasca

    jlabrasca

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    That seems likely. The heavier motor pushed terminal speed past the alarm limit.

    The heavier rocket will not only have a higher terminal speed, it will take longer to accelerate to terminal speed. It doesn't seem as likely, but it may be that main deployment for the larger motor is happening before the rocket under drogue reaches terminal speed.

    https://www.rocketryforum.com/threa...y-have-to-morph-into-hpr.146005/#post-1786551

    (What kind of tool quotes himself on an internet discussion board)

    It comes to the same thing though, the heavier motor means higher speed at deployment.

    EDIT: Got my smallers/largers, heaviers/lighters all tangled up.
     
    Last edited: Sep 11, 2018
  2. Sep 11, 2018 #212

    jqavins

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    All makes sense, and seems plausible as an answer. Coincidental that the speeds with the smaller and larger motors just happen to straddle the limit, but the limit had to be somewhere. If this is the explanation, then increasing from at 18" to a 30" drogue seems a bit drastic. (It's about 2 3/4 times the area.) A 24" (1 3/4 times the area) should be plenty.
     
  3. Sep 11, 2018 #213

    snrkl

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    Much simpler explanation of the jump
    from 18” to 30”:

    You see, I didn’t test anything between 18” and 30”...

    I saw that 18” was too small, and 30” is the next size chute I own!!

    So my statement “I had to jump to 30in” was more a limitation of personal resource availability than any scientific need for 30” specifically!! [emoji12]
     
    Last edited: Sep 11, 2018
  4. Sep 12, 2018 #214

    jqavins

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    Yeah, I got that. What I meant (and I was really not clear) is that since 30 is probably excessive, and you did mention that you're considering buying a 30" with a spill hole, if you go with buy, then buying a 24" might be a better idea. 30" could give you a considerably longer recovery walk.
     
  5. Sep 12, 2018 #215

    snrkl

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    Ah yes. I see your point. Well played sir.. well played...
     
  6. Sep 12, 2018 #216

    HASTE

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    CACTUS; Can't Actually Confirm Totally Un-Serviceable.
    But I guess ?
     
  7. Sep 15, 2018 #217

    snrkl

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    Ok - root cause analysis of my rotary switch failure was badly planned and executed soldering of the leads to the pins.

    Long story short, I hadn’t unpacked my helping hands when I soldered, so the joins were messy. I also didn’t think of wire directions, so the leads were heading straight in, and collided with the RRC3 when it was mounted. I tried to overcome this with eleventy layers of progressively larger heat shrink, which I think actually made it worse, as the additional mechanical rigidity pushed all the forces straight to the top of the part, which was the solder join.

    I’m now trying to think how to overcome this.

    Initial step is easy, invert the direction of the sled, so the rotary switch comes in from behind the sled, reducing the amount of stuff that the wiring harness could collide with when inserting/removing the sled.

    The next thought was to make the wiring harness solder joint at right angles to the rotary switch, so the lead naturally follows down the inside of the eBay heading aft, rather than having to make a 90° turn.

    Then my thoughts went to some kind of something to support the 90° solder and encase the airframe/switch from the inside; then I remember this thing has to screw into the side of the airframe, and a giant L shaped inside bracket /wire join won’t exactly be easy to screw in.

    How do others use the rotary switches mounted to the outside of the airframe without killing wire connections?!
     
  8. Sep 15, 2018 #218

    Andrew_ASC

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    Try a magnetic switch? IDK.
     
  9. Sep 15, 2018 #219

    boatgeek

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    AMW had a layout where they soldered the wires to two terminals each at 90 degrees to the switch axis. You could probably find a diagram on their site. The only long term solution that’s worked for me is to mount the switch to the sled and reach in through the hole with a screwdriver. Or use a screw switch.
     
  10. Nov 11, 2018 #220

    snrkl

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  11. Nov 11, 2018 #221

    snrkl

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    In the end I just soldered the wires at 90° to the pins and ran the harness around the underside of the sled.

    I inserted some dowel into the heat shrink that ran up to the 90° solder joint and passed it between the opposing pins, which I then bridged with a wire and soldered across, so any mechanical strain is being shared across all 4 pins. The dowel is pinned between the shorted pins and the wrap on the active wires. Best solution that I could figure out.
     
  12. Nov 11, 2018 #222

    timbucktoo

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    Congrats man!
     
  13. Nov 11, 2018 #223

    Tyler P

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    I spent some time reading through this whole thread and thoroughly enjoyed it. Your attention to detail is excellent!

    Very nice build and super helpful thread for me to refer to!
     
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  14. Nov 11, 2018 #224

    snrkl

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    Thanks!
     
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  15. Nov 11, 2018 #225

    jlabrasca

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    Congratulations.
     
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  16. Nov 12, 2018 #226

    snrkl

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    And here is the flight video:

     
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  17. Nov 12, 2018 #227

    jqavins

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    Congratulations, and well deserved.
     
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  18. Nov 12, 2018 #228

    Nytrunner

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    Good job!

    *I didn't realize "Far Out" was actually spoken anymore
     
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  19. Nov 12, 2018 #229

    Tyler P

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    Fantastic video and congrats on L2!
     
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  20. Nov 12, 2018 #230

    snrkl

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    That was my partner’s nephew. He’s a crackup... he built (and lost) his first rocket, an 18mm MD...

    It’s funny - the last launch of the day was his C6-5 flight. His airframe was suffering from glue melting a little from the A8-3 and B6-4 flights that preceded, and the motor grabbed 2/3rds of the way in.

    I decided it was a teachable moment, so I sent him off to the pad.

    He got a practical example of a rocket that’s unstable for the first 1/2 a second before the motor burned enough to have the CG in the right place: it went crazy for 1/2 a sec then shot out over the corn field.

    He looked at me and figured it out all on his own; the CG/CP relationship suddenly made sense to him!
     
  21. Nov 12, 2018 #231

    neil_w

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    Ditto and ditto!
     
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