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  1. #1
    Join Date
    3rd February 2010
    Posts
    92

    Eggtimer TRS GPS antenna broke off, fixable?

    Flew my Eggtimer TRS today for the third time and the GPS antenna broke off from the GPS board. Flight was pretty tame, 5lb rocket to 800 feet on a mid H, nothing fancy, landed under full chute nice and slow.
    It looks like it pulled the solder pad off with it when it went.

    Is this repairable? Is there an alternate way to mount a patch antenna or something, be a shame to have to scrap the board.


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  2. #2
    Join Date
    3rd February 2012
    Location
    So Cal (ROC, TRASD, SCRA)
    Posts
    2,517
    Sadly, no. I've tried several different methods over the past few years to fix this common problem, no luck. The antenna is held onto the metal can with a strip of double-sided conductive adhesive tape, this is a common mounting method for these antennas. The problem is that when the antenna breaks off it usually takes the plate-through on the center conductor with it (note the little "mushroom" at the end of the pin), so the trace that leads to the antenna is toast. Your recourse is to replace the GPS module, which is actually not that horrible if you have a hot-air rework tool. Email support@eggtimerrocketry.com and I'll tell you all about it.

    This is why in the latest instructions for all the GPS trackers I am recommending that you run a fillet of good epoxy (such as RocketPoxy or West) around the base of the antenna connecting it to the metal can. It took me about 3 years to come to the conclusion that this is the best way to attack this problem... I've had people actually lawn dart rockets with Eggfinders in them, and they survived because the antenna couldn't come off.


  3. #3
    Join Date
    11th January 2012
    Location
    Commonwealth of VA
    Posts
    1,528
    Cris,

    Is heat shrink tubing also effective at preventing this?

    -Bill Riley

    TRA: 12294
    NAR: 89196

    A good rule for rocket experimenters to follow is this: always assume that it will explode.
    Astronautics, issue 38, October 1937.


  4. #4
    Join Date
    3rd February 2010
    Posts
    92
    Ouch. Thanks for responding quickly though. I checked through the Eggtimer TRS A5 and G2c assembly manuals to see if there was something I missed and neither mentioned the epoxy trick. I see that it is mentioned in the Eggfinder Mini instructions though.

    I will have to check if I have access to a hot air rework tool at one of the maker spaces, but I don't have one.

    I'll e-mail you offline to see what my options are.

  5. #5
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
    Posts
    1,148
    If the flight was otherwise nominal, maybe it was the ejection charge that caused it.

    The usual recommendation for this is to epoxy the top of the antenna to the PCB. This, of course, should be done before flying the unit. I run a small amount of West System around the base as it is what I have on-hand.

    I think heatshrink would help to a great degree. Personally if I wanted to heatshrink I would epoxy as well.

    As for the repair, I will defer to others' experiences.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  6. #6
    Join Date
    26th November 2009
    Posts
    4,606
    I busted the GPS antenna off egg Finders, three of them actually and it can be restored but it's pretty difficult. A TRS
    Would be pretty hard to do. Basically to restore an egg finder one has to get the base off the board and then find the pad for the transmitted out on the new GPS chip set and solder a wire into it. Ostensibly, this is not a stock GPS replacement. One usually manages to mangle some of the pads in the process of removing the base off the board. In that case only an outboard GPS chipset can be used. With the crowded space on the TRS it would be really hard to do a swap or repair.
    Sorry about the mishap. Like Cris mentions, it's a reasonable idea to lay a bead of epoxy of some kind to try and support and hold the GPS antenna to the base. Heat shrink tubing is better than nothing but I don't think there's anything that can beat a solid bead of epoxy. Kurt

  7. #7
    Join Date
    3rd February 2010
    Posts
    92
    The procedure to remove the GPS module from the board looks to be fairly straight forward with a hot air rework tool, so I am going to check the maker space this week to see if they have one I can use, otherwise I imagine a couple of the electronics guys in the club would have one.
    Now just trying to confirm if Cris is sending me a new GPS module.

    When the repair is done there will be epoxy reinforcement.

  8. #8
    Join Date
    26th November 2009
    Posts
    4,606
    Quote Originally Posted by kclo4 View Post
    The procedure to remove the GPS module from the board looks to be fairly straight forward with a hot air rework tool, so I am going to check the maker space this week to see if they have one I can use, otherwise I imagine a couple of the electronics guys in the club would have one.
    Now just trying to confirm if Cris is sending me a new GPS module.

    When the repair is done there will be epoxy reinforcement.
    By all means share your results. I haven't worked with a hot air rework device before but I'd be concerned that some of the components near the base could be affected. I'm not an electronics wonk so would be interested what it takes to pull off.
    The Maestro GPS is pretty cheap I last recall. Perhaps Cris can comment? I believe the solder he gives us is of the low temp variety and that would be the best bet for removal.

    Me? I used a cutoff wheel and carefully split the base in half to the board. I then laid the side of the soldering pencil against all the contacts until the "half-base" fell off. Did the same to the other side. Now this was with the EggFinder and might be
    a whole lot harder to do this crude removal process with a TRS. If you can get the repair process done for less than the cost of a new unit, you'll be coming out ahead. (Plus you don't have to go through the hassle of building another one. But then again, I found them fun to build.) Again, keep us posted. At least you got some flights out of yours. My first EggFinder I broke 30 minutes after I completed the build. It was working perfectly and I was excited as all get out. Went to pull it off the windowsill and it
    slipped and landed on the floor. Yup, the GPS antenna broke off. Nope, I wasn't inebriated either. Was a Sunday afternoon and got Xastir to decode the positions as a local GPS source. I tossed it in my junkbox and on a whim a year and a half later I dinked
    with getting the base off and wiring in and outboard GPS. Tried some Ublox chipsets and surprisingly the timing is a bit different so the GPS altitude doesn't get displayed properly on the EggFinder LCD. The information is in the raw strings though and the lat/long is dead on. Kurt
    Last edited by ksaves2; 10th September 2017 at 06:36 PM. Reason: added stuff.

  9. #9
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
    Posts
    1,148
    I am with Kurt on this one for rework. Usually the better way to remove a defective part is if you don't care about damaging it. That lets you get really careful with the PCB that you want to survive the operation. Hot air rework tends to heat everything up, especially with ground-plane boards, unless you have something like a back-heater to prewarm the planes before applying the spot heat. I can do this at work, but I have the right equipment. I prefer to mechanically cut away what I can and then remove the hacked bits of the defective part, leaving the main board relatively pristine.

    I can't remember the details of this board. It may be more amenable to hot air rework due to the low melting-point solder and layout. Have a good think about your equipment and capabilities too. Choose and have a go!

    Good luck with the repair and please let us know the results.

    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

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