Mounting Featherweight GPS

Discussion in 'Rocketry Electronics and Software' started by rewilfert, Mar 29, 2019.

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  1. Mar 29, 2019 #1

    rewilfert

    rewilfert

    rewilfert

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    I am working on a mount for my Featherweight GPS. The unit itself mounts with 2 holes through the PCB. Has anyone seen a need to provide any type of additional support for the long radio antenna that comes off the top of the unit? It is light and the mount that the antenna screws into seems very secure on the PCB. If no one has had any issues with the antenna breaking free of the board, I may just leave it alone.
     
  2. Mar 29, 2019 #2

    Wayco

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    No issue with the antenna, we have made thirty flights with the Featherweight GPS, including several Mach+ flights. Very durable unit.
     
  3. Mar 29, 2019 #3

    Cl(VII)

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    Chris Bender, Lab Rat

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  4. Mar 30, 2019 #4

    rewilfert

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    The part that the antenna screws into looks very solidly mounted to the PCB and the antenna itself is very light weight. Good to know that it holds up well in service.

    Those sleds look nice but probably wouldn’t work for where I need to mount the GPS. I’m also using a 9v battery instead of the LiPo that came with the GPS. Good to know these options exist for future reference though. Thanks!
     
  5. Apr 8, 2019 #5

    rewilfert

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    I heard back on this from Featherweight and no antenna bracing is necessary.
     
  6. Apr 8, 2019 #6

    Viperfixr

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    Lost my on-board, Featherweight GPS tracker yesterday using this sled. Launched without a GPS lock as it was a redundant tracker, but the top of the sled with the eyebolt was the only thing recovered. It was connected to the nylon recovery harness.

    I have a nylon sleeve with kevlar cord (sold on rocketry planet years ago) that attaches to the recovery harness that I have flown with great results many times with my BigRedBee HAM trackers. Now I just need one sized for this GPS tracker.
     
  7. Apr 9, 2019 #7

    BDB

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    Are you saying that the eyebolt broke through the plastic, so you lost the sled, tracker and nosecone? Did you use the FG bulkhead for reenforcement?
     
  8. Apr 14, 2019 #8

    AeroAggie

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    Yes, please share more details about your configuration. I'm designing some nose cone sleds for 3D printing right now, fairly similar to LabRat's in that the bolt passes through the sled base. My test prints seem stout enough but I'll always worry about layer separation on the 3D printed stuff.
     
  9. Apr 14, 2019 #9

    Viperfixr

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    My intent here is to share my experience, not to leave negative comments about any brand/label. Everyone biz in HPR is small and home-grown with good intent. TFR gets ugly all too often and I don't want to add to that.

    Yes, the only thing left of the sled was the eyebolt. My sled did not come with FG reinforcement. Don't know if this changes anything, but I bought one of the first units available. That said, I don't think I will trust plastic to this task in the future, with FG reinforcement or not. And, lesson learned, I will never launch a GPS tracker without a lock, redundant or otherwise. The launch congestion and timing at RED GLARE compelled me to move along as is--$150 lesson. A new Featherweight GPS tracker is on the way.

    Reason why I had a tracker GPS lock problem was that I didn't connect the ground station/phone until after it was secured in the rocket, shear pins in place and all. When I did, the app immediately took me to a firmware update without an option to skip. That didn't take long, but the ground station required a recycle of power afterwards to function. I did not open up the rocket to do the same for that tracker. I wish there was an option to skip a firmware update, perhaps reasserting the update option every time the app is opened.

    Just to be clear, the reason the tracker was lost was entirely mine, not Labrat or anyone else. We need Labrat rocketry and all of the other home-grown businesses that keep our community thriving. If I'd opened up the rocket and recycled power on the tracker, it likely would have been found.

    The tracker sleeve I use for my BigRedBee HAM units was bought on Rocketry Planet years ago and has flown dozens of times without a fault. It is made of 1.5" tubular nylon webbing with sewing to allow the unit to fit inside snugly, with a cord at the top to connect to harness. I just bought 2" nylon webbing, grommets and kevlar cord with the Featherweight GPS unit in mind, and think it will work just as well. I am also considering a 3D printed exo-skeleton for the tracker to snap into before going in the sleeve, to minimize potential impact damage. Work in progress.
     
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  10. Apr 14, 2019 #10

    AeroAggie

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    Thanks for the update! I don't think the LabRat sleds come with a fiberglass bulkhead - you're supposed to use one from your kit to reinforce the joint. All of this is a learning experience and the hobby is constantly evolving to use new materials and methods. I'm not looking to make this a negative experience either, but if you use a product and break it, then I think it's prudent to share your experience with other uses and the vendor to characterize the failure modes and develop a better product.
     
  11. Apr 15, 2019 #11

    Cl(VII)

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    First let me say, I appreciate the intent of not turning this into a flaming...thanks very much for that. So I can better understand what went wrong, I'd like to ask a few questions too. Were you using the nosecone mounting, or the shockcord sleeve mounting? Also, you say the only thing left was the eyebolt, so that means that the base of the sled would have fractured such as to release it completely from the eyebolt, correct?

    For clarity, the use of a fiberglass bulkhead (or a washer) is suggested in the case of the 38 nosecone bulkhead, but not in the case of the shockcord mounting sleeve. That said, I've see pictured of the 38 and 54 bulkheads that survived ejection events well after apogee, like terminal velocity after apogee, that survived. Therefore, I'm betting this was a shockcord sleeve case.
     
  12. Apr 15, 2019 #12

    kjs

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    First, as Chris said - we appreciate your helpful honest feedback without getting negative - thank you!

    Second, noted on the option to bypass a firmware update... This recent update was more complicated being the first real firmware update, and including channel changes from Adrian to make it FCC compliant. To support old and new firmware, I would have to had supported both old and new channels and some other communications changes. I can understand wanting to skip the update though so will try to incorporate 'fall back' support in the future when possible.

    As an aside, the thread I just posted about the first lost/found rocket had a similar feel to it where the tracker separated and even had a broken antenna. My next rocket happened to pick up it's lost rocket transmissions though and I noticed them later. If your tracker didn't have lock though, I doubt it would have started sending "I'm lost" packets (it wouldn't have detected launch without lock).

    Thanks for the feedback!

    /kjs
     
  13. Apr 15, 2019 #13

    Cl(VII)

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    Out of caution, I have temporarily (maybe completely pending redesign) removed the shockcord sleeve mounting option for this sled.

    I've only had one other report of a shockcord sleeve on any model breaking, so two on the same model has me wondering. The other was a teleGPS where the sled/sleeve landed before the large fiberglass booster, and got very unlucky about the boosters chosen landing spot. All parts were recovered together, and the tracker was fine in that case, i.e. clearly a ground event. The flyer and I both took it as a "stuff happens" kind of thing, and I replaced his plastic.
     
  14. Apr 16, 2019 #14

    kjs

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    Going back to the original post, I can say I have flown the tracker a number of times and never had extra bracing for the antenna.

    As far as mounting, I usually put a 38mm tube in the nose cone with kevlar down the side. I attach to the kevlar and use an aeropack retainer to hold the tracker in the nose. Recently I got a 3D printer so the attached pic is my first Tracker board sized to work with the aeropack retainer and an o-ring for the seal. I still use black tape for the battery (instead of making a 3D 'compartment' for it) because I like it to have zero or little movement. Anyway, this allows me to easily move my tracker to another rocket. [Picture attached - I don't seem to know how to insert it 'inline'...]

    I'm also doing something similar with the Raven4 on a Power Perch. It is again held in place with an Aeropack retainer and I use O-rings to seal the forward ejection charge.

    Yes, I spend a bit of money on Aeropack retainers... I might need to come up with a 3D print for that as well... :)
     

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  15. Apr 16, 2019 #15

    Viperfixr

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    Yes, it was shockcord mounted via a quick link through the eyebolt and packed in the lower airframe along with the drogue and the rest of the recovery harness. When I say only the eyebolt was left, I mean no plastic was still captured at all--it was the quick link and the eyebolt on the harness without any orange plastic left. I searched the field for a while, but apogee was at 9080' AGL and I figured it was a long way away from where the rocket landed on a windy day.
     
  16. Apr 16, 2019 #16

    Cl(VII)

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    Wow, something very violent happened there (that is not to say that your ejection was violent, just that something locally violent happened to the sled). Breaking in that manner is particularly difficult as there are many circular paths taken when the filament is laid down. Interlayer adhesion issues lead to the z-axis being the inherently weakest in almost all 3D prints, but this is not a failure in the Z-axis. A few more follow ups if I may:

    Was the eyebolt tight in the base of the sled, i.e. the eyebolt was cut to length, and tight?

    What diameter was the rocket (I'm wondering if the sled could have momentarily bound "sideways" in the rocket on ejection leading to the destruction)?

    Is there any chance the sled/shell was in direct contact with the ejection charge?

    Thanks for any details you can provide, these are very helpful in understanding how to improve things.
     
  17. Apr 19, 2019 at 12:31 AM #17

    rewilfert

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  18. Apr 19, 2019 at 12:45 AM #18

    Viperfixr

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    Short answers:
    - Eyebolt was tight, cut to two threads above the nut and not 'crack plastic' tight
    - 4" Wildman Jart (extended airframe--lots of room)
    - No, the sled was purposely put between some dog barf (below) and the drogue+harness (above)--it was well shielded
    The sled was connected to the harness via the eyebolt, but loosely so that it could move as needed.

    New tracker here and ready for LDRS!
     
  19. Apr 19, 2019 at 2:17 AM #19

    Cl(VII)

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    Chris Bender, Lab Rat

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    Thanks very much for the feedback.
     
  20. Apr 19, 2019 at 1:58 PM #20

    Buckeye

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    So, the sled could slide freely up and down the shock cord? Perhaps at ejection it crashed into the upper airframe.

    Not a big fan of putting electronics on a shock cord. I always put my altimeters and GPS devices in an av-bay secured in the airframe/nose.
     
  21. Apr 19, 2019 at 2:03 PM #21

    Banzai88

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    My universal carrier gets clipped on, and then gets a wrap of duct tape around it and the shock cord. Anything that's gonna kill that will also result in trash bag recovery.
     
  22. Apr 19, 2019 at 2:34 PM #22

    Buckeye

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    Curious about the orientation of your 9V battery. I have the contacts pointed down to guard against high axial acceleration at lift-off and possible separation of the contacts from the holder. The contacts pointed up would prevent battery separation under high axial acceleration in the opposite direction, say during ejection when the rocket is nosed over. I think the former is the more extreme case.
     
  23. Apr 19, 2019 at 4:59 PM #23

    rewilfert

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    The battery holder I used captures the battery on both the top and bottom. You have to force the battery into the holder, it is a very tight fit. The zip tie keeps the battery from being forced out the side of the holder. I went through your same thought process and for this holder the orientation of the battery doesn't matter.

    https://www.digikey.com/product-det...0YXhxRHJZa1J2NmprUDc1SE9RNFFVU3FoOVlWQkNqIn0=
     
  24. Apr 19, 2019 at 5:32 PM #24

    TonyL

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    I was able to bend my antenna: the nosecone separated and came in like a football from 27kft and hit the dirt without bouncing much. That bent the antenna about 10 or 15 degrees relative to the board. Two out of four soldered legs on the sma pulled up from the pcb. I was able to carefully straighten it, and it seems fine otherwise. I potted the base of the sma connector to provide some support so the center pin wouldn't move around.

    I now use it for 'high risk' flights. I extend the phenolic backing board to reach up to the antenna and I hot glue the tip to the board to help support it under side impacts. I also RTV'd the battery to a piece of 1/16" phenolic to give it mounting holes and a more distributed support. [my flights with it have been in the 30-80g range].

    Under normal flight conditions none of this should be necessary, but my unit had good track essentially to the ground coming in ballistic, so I expect to be able to find the pieces most of the time :)

    br/

    Tony
     

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