Little Joe II A-003 Mission Build

Discussion in 'Low Power Rocketry (LPR)' started by srfrich, Apr 21, 2019.

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  1. Jul 6, 2019 #61

    mikec

    mikec

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    Most electronics are insensitive to magnetic fields from these magnets, which are pretty localized. For example, R/C planes often use magnets to hold hatches on right next to their receivers and ESCs. Exceptions would be anything that senses magnetic fields deliberately, like magnetic apogee detectors.

    I'm not seeing how moving the magnet would cause the BPC to come off, though, at least not during boost, since it would still be held on by aero forces.

    I've long thought about a staged Little Joe II but I wouldn't try it on a model this small.
     
  2. Jul 6, 2019 #62

    georgegassaway

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    Nearly 30 years ago, I modified my old beat-up Centuri 1/45 Little Joe-II for "Abort staging". I modified the BPC cone to hold an engine mount in the base of it, plus a rear eject system to deploy a parachute to recover it. And added a mercury switch system into a 1" long ejectable piston that fit in the upper part of the SM, just under the BPC cone, to both house the electronics and to keep the recovery system of the Main Body from being roasted by the A3 engine inside the BPC. It flew and worked out just great. Later I did a similar BPC Abort test with a 4" model, and C6 engine in the base of the BPC. It worked, but I decided not to pursue it for Contest models due to the reliability risks.
    [​IMG]

    I've never done an air-start staging, though. IIRC, Tom Beach did. I think it was an A-003 model, taking off on three C6's and then igniting 3 more C6's when the first set burned out.

    Here's something I've done a couple of times. A slightly smaller than scale Command Module, that fit inside of the BPC cone of my 4" (1/39.5) scale models, that came out after ejection. Using three parachutes, a tracking beacon, altimeter, and a live video camera looking thru the hatch window. Did it for extra scale mission points. [​IMG]
     
    Last edited: Jul 6, 2019
  3. Jul 8, 2019 #63

    srfrich

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    That's actually very encouraging about the insensitivity to magnetic fields.

    Yeah, but the flight plan idea was to jettison the LES after main ejection, not during boost, so was really not a 'staged' LES like you were thinking of, but an unpowered separation.
     
  4. Jul 8, 2019 #64

    srfrich

    srfrich

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    Impressive. And some inspiration for future builds. :cool:
     
  5. Jul 8, 2019 #65

    srfrich

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    Thanks for that. First, I should see if the basic air-start idea will fly; then branch out into more difficult add-ons, like the LES jettison. After all, a LJII kit is only $40, less than the cost of the 6 D motors!
     
  6. Jul 9, 2019 #66

    srfrich

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  7. Jul 14, 2019 #67

    srfrich

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    I took your word on that, and tested the electronics with two large neodymium magnets taped inside the base of the BPC. I heard the arming tone when I armed the system with the RC controller.:cool: IMG_1072.JPG After verifying that the magnets don't affect the electronics, I encased the magnets in 5/16" styrene tubing. IMG_1077.JPG IMG_1073.JPG
     
    Last edited: Jul 14, 2019
  8. Jul 14, 2019 #68

    srfrich

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    Spent the rest of the 'work day' tediously improving the fit of AVbay components with a Dremel. Had to sand down the corners of the PCB some more. It's a mess (nothing precision here), but fits comfortably now, and won't be frustrating for me at the launch site. Here are channel A and B outputs protruding through the base of the Apollo capsule. IMG_1078.JPG 2mm Gold Bullet female connectors soldered to the pins of the terminal block. IMG_1081.JPG IMG_1080.JPG Channel (A) is for the air-starts. Tweaked the male connectors for (A) so that they pull out with just a bit of force, freeing the capsule from the ignition leads that will run the length of the booster to the motors.
    The (B) channel connectors will be factory tight, for an e-match pair that runs to the base of the laundry room. The (B) channel is for an 'abort' command, or for ejection at apogee (visual). I don't mind a burned e-match hanging from the capsule during descent.
     
    Last edited: Jul 14, 2019

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