AV-Bay Newbie

Discussion in 'Rocketry Electronics and Software' started by Arsenal78, Aug 7, 2018.

  1. Aug 7, 2018 #1

    Arsenal78

    Arsenal78

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    I am going to be attempting my L2 in November with a BSD THOR, and after gluing all the tubes and couplers together since I plan to fly motor eject with a Jolly Logic Chute Release, I realized I actually do want the choice of having an altimeter bay.The rocket actually has a smaller body tube to house one (or at least the instructions call it an av-bay), however being all glued together, I think I screwed myself lol. Can I cut where the body tubes meet, somehow rip the couplers out (glued with Titebond 3) and put new ones in? Also are there any good videos or links to building an AV-bay? I'm assuming the coupler is held in the body tubes with removable rivets.
     
    Last edited: Aug 7, 2018
  2. Aug 7, 2018 #2

    Rainmaker

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    Apogee has a pretty good series of videos on building a level 2 rocket showing rivets, shear pins, and the AV bay construction. Good to get you started and pointing you to more specific questions.
     
  3. Aug 10, 2018 #3

    FMarvinS

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    Given the fact that you have already epoxied the coupler tube in place (presuming both forward and aft ends between the booster and payload sections), you may want to consider a nose cone placed AV-bay. In this way it can facilitate the use of the chute release. If you look at the build thread created by CJ starting in post #17 (https://www.rocketryforum.com/threads/cj-builds-wm-mach-2-rocket-2-stage.144264/) you'll see an excellent example of such a bay. This bay as pictured utilizes one set of BP charge ejection tubes on the aft bulkhead; so you could epoxy the forward end into the nose cone or hold in place either with plastic rivets or via 3 flat headed 6-32 machine screws placed into counter sunk holes on the nose cone surface to be screwed into epoxied nuts or flat T connectors on the inside surface of the coupler. When the altimeter senses apogee the charge would separate the nose cone/AV-bay unit from the payload tube freeing the main chute bundled by the chute release. Afterwards, the chute should fully deploy at the altitude you set the chute release to. In this scenario, the caveats are the size of the nose cone to accept the coupler and that the vent holes are placed through the switch band just below the nose cone base.
    For future builds, as pointed out by Rainmaker above, Apogee components has a tutorial and the following from CJ (see posts 41 to 43) and Mad Cow Rocketry may be of interest
    https://www.rocketryforum.com/threads/how-to-build-a-stock-3in-darkstar-cj-step-by-step.55019/
    https://www.madcowrocketry.com/content/pdf/fgalt26removable.pdf

    Good luck with your L2!

    Fred, L2
    member of ICBM,
    Camden, SC
    KG4YGP
     
  4. Aug 10, 2018 #4

    Arsenal78

    Arsenal78

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    I used Titebond 3 on the whole build minus rocketpoxy external fillets. I don’t plan to do dual deploy for quite a long time. Bought the AV bay for future gps
     
    Last edited: Aug 10, 2018
  5. Aug 10, 2018 #5

    Zeus-cat

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    You could cut the tubes at a point away from the couplers and install the av bay at the cut. Make sure you leave enough room so that the av bay shoulders don't hit the glued in couplers.
     
  6. Aug 13, 2018 #6

    Bat-mite

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    Personally, I would go ahead and certify with the JLCR and then build a DD rocket later. Cutting tubes is tricky, and with glue all over the coupler, even if you sand it down, there is a risk that it won't slide smoothly in and out of the airframe.
     
  7. Aug 13, 2018 #7

    Arsenal78

    Arsenal78

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    I don’t plan to do dual deploy at all, just the chute release but I want to put a GPS in it for future use
     
  8. Aug 13, 2018 #8

    Bat-mite

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    Sorry I misunderstood. A couple of easy ways to add a GPS tracker are as follows:
    1. Put the unit in a small plastic case and tape it thoroughly to the harness above the chute protector.
    2. Cut a portal in the NC shoulder, put the tracker into a long piece of foam rubber pipe insulation, and shove the hole thing into the NC. Tape over the hole.
     
  9. Aug 13, 2018 #9

    Arsenal78

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    Does a chute release require a vent? I know an AV bay does. Thinking about putting an altimeter in the AV bay as well. Had considered the Jolly Logic Altimeter 3 but that needs a vent in the booster tube where the chute goes as it connects to the parachute
     
  10. Aug 14, 2018 at 1:31 AM #10

    OverTheTop

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    It should already be blowing in the breeze, but keeping the chute furled.
     
  11. Aug 14, 2018 at 6:09 PM #11

    Bat-mite

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  12. Aug 15, 2018 at 6:52 PM #12

    woferry

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    I'd add two remarks to this. It's certainly true that the Chute Release doesn't care about vent holes, by the time it needs its altimeter you should already be descending, and had better be separated by that time or the CR won't help anyway. But there are still two reasons to consider venting, in my opinion:

    1) Avoiding pressure separation. Depending on how tight of a fit your AVBay is to your airframe and the volume of the parachute section, you can end up with a significant pressure difference between the at-altitude air surrounding the rocket and the ground-level-pressure air "trapped" inside the rocket. So you could end up with an early separation caused by this pressure difference, which can be mitigated by venting the parachute section (to give the air another path out of the airframe), or shear-pinning the parts together, or perhaps something like friction-fitting (but you need to ensure things can still separate when the charge fires without just blowing your airframe apart). I typically vent airframes for this reason even when there is no altimeter/CR to worry about.

    2) A much more minor concern but one that I think tripped me up once, if, once you arm the CR and seal-up the parachute section, you need to re-open the bay, it seems that you can generate enough of a pressure drop in the airframe to make the CR think it exceeded and then passed below its programmed altitude, causing it to release in the airframe. So if you don't re-check the CR before flying, you might find that it's already released and have your main deploy at apogee. So at least you're going to land under chute, but it might drift a lot farther than you intended. I had one time where my CR released early (well, twice, but the other time was clearly a band that broke during separation, this time the band was intact), and the only thing that was different about this flight vs. the many successful flights on the same rocket/CR was that the RSO asked me to demonstrate that the NC could separate as it was a very tight fit on the rocket (always has been). I do have a small vent hole in this airframe, but you can hear it "breathe" whenever I insert or remove the NC, and I suspect I still get a good pressure dip since it's hard enough to remove that once it breaks free it moves quickly.

    It's also worth noting that the AltimeterThree doesn't have to go in the booster tube, I fly it in my avionics bays whenever I can (whenever I have the space), to shield it from the ejection charges.
     
  13. Aug 15, 2018 at 10:17 PM #13

    davdue

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    I use a Big Red Bee BRB900 GPS tracker in my rockets. Since these are all already dual deploy I had to convert them for use with the tracker. I cut the bottom of the nose cone shoulder off and made a plywood bulkhead plate that is epoxied in the end. It has a U-bolt in it for attachment to the shock cord. I built a sled for my tracker and used a small piece of aluminum angle iron to mount it to a another plywood bulkhead. The nose cone bulkhead has a hole just big enough for the tracker sled to slide in and then I put T-nuts in it that the tracker can screw into. Each rocket is set up the same way so I can easily move the tracker from rocket to rocket. I will see if I have any pictures of my setup or take some and post them later when I get home.

    Here a some pics I took last night.

    BC6A0E94-751A-47B2-909B-7BFDB7A46370.jpeg F24FCF86-6366-4336-908D-40EF1F15DA75.jpeg 638E38E8-2BE4-4471-9C91-4E5C434C048B.jpeg
     
    Last edited: Aug 16, 2018 at 2:42 PM

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