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No longer a proper GPS lock

Discussion in 'Phantom 1 Discussion' started by st2430, May 10, 2014.

  1. st2430

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    Up until recently I haven't had any problems with the GPS but then suddenly I could no longer get a fix with no red lights. I've had a few minor crashes and reading somewhere else it looked as it could be a cracked GPS unit. So I bought some spare ones from Digi-Key and after changing the existing one (which had no visible damage) I now get a better lock, down from 2 red blinks to one. But in the past I had no problem getting a full fix after just 10-15 seconds. Btw, a compass calibration doesn't help. Suggestions anyone what this could be?

    Sent from my HTC One using Tapatalk
     
  2. OI Photography

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    1. Did you reinstall the grey insulated foam liner when you put the GPS board back in place?

    2. Are you testing in the same location(s)? The results I get on my bench are inconsistent enough that I need to go outside to get reliable ones.

    I actually have a couple of those same antennae arriving today from Mouser. I'm replacing mine due to deteriorating precision in holding position, and these weird burn-like marks I found on the current one:

    [​IMG]
     
  3. st2430

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    1. Yes, I replaced the foam

    2. Yes, I'm on the same place outside from where I've flown several times before with no GPS problems.

    The mobile phone gets a fix within 5 secs, but of course it has assisted GPS. It's shame that A-GPS is not used in the Phantom.

    The marks on your unit look odd indeed, was it installed by dirty fingers? :) My unit looks new but I changed it anyway.

    I noticed when I tried yesterday that I first got 3 red flashes, then 2, then after a long wait 1, then it suddenly went back to 3 and after that 2. This erratic behaviour is worrying, I call myself a beginner and am not that confident flying in attitude mode yet. But taking off with a GPS that one cannot trust is not really what I want :(
     
  4. Dalite

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    If you are using a GoPro, try it without the GoPro turned on and see if there is any difference.

    I unplugged my compas cable and loosely twisted it until the coils reached all the way to the GPS board, then reconnected it. I also did the same with the GPS servo cable going o the NAZA.

    The GoPro creates a lot of electrical hash. Trying to introduce some basic shielding to the compas cable may help, as the compass data daisy chains through the GPS board to the NAZA.

    Also, the backup battery on the GPS board may be below the 1.8 VDC minimum to be an effective part of the circuit. According. The uBlox design and integration info, if resistance is detected across the battery backup terminals, GPS performance could suffer.

    On 2 new FC40s that I have, one measures less than .5VDC and the other was .025 VDC.

    If GPS data stored in RAM is becoming corrupted due to a failing backup battery, the first flight of the day may take an extended time to do a basic cold start; after unsuccessfully reconciling the corrupt data with the new data coming in once the main Battey is onected.

    Before I put the GoPro in a H3D2 gimbal, I could remove it, turn it on, and place it close to the phantom body to induce sat lock loss. Place it near the top and get total loss; near sides or bottom and get partial loss.

    Add a gimbal to the mix, and the GoPro may be rotated closer to a poorly shielded data cable and do the same in flight.

    When you look inside the Phantom, you will probably see where DJI twisted the servo cables going from the receiver to the NAZA. This seems like a good enough recommendation to give the other NAZA input cables the same treatment.
     
  5. st2430

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    Thanks for these tips, I will follow them up. As I haven't been flying for a while (I've been away from home) I just realised that I haven't flown since I installed a FrSky voltmeter so I can get the current voltage reading to my mobile while flying (using app FrSky Dashboard). Reading about your advice to twist the cables I'm beginning to believe that the voltmeter may be causing this problem. It came with fairly long cables and I made no attempts to twist or hide them away from the GPS unit and its cables. This is definitely worth investigating. I'll report my findings once it's done.
     
  6. st2430

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    Wow, that was it!!! I had installed the cables for the voltmeter so they actually touched both the GPS cable and the compass cable, not very clever I can say now when I've learnt something new. So I rerouted the wires away from all this, twisted the GPS and compass wires, connected the battery and - about 5 secs after the warm up sequence I now have a steady blinking green light. Unbelievable. Thanks for hints and tips! :D
     
  7. OI Photography

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    That requires adding Bluetooth to the FrSky Tx module, correct? Are you using the DJT or the XJT? I'm thinking about doing that with mine but wasn't sure how much of a pain it was to modify for that.
     
  8. st2430

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    Yes, bluetooth is needed. This is my set-up:

    Phantom v1.2 (without the DJI tx)
    Turnigy 9X tx running er9X
    FrSky DJT + D8R-II
    Bluetooth HC-05 RS232 (Ebay $20)
    FrSky Voltage meter

    I've taken away the original antenna from the tx as the DJT has its own, installed the bluetooth unit inside the tx with the cables passed through the hole where the antenna was located, to be connected to the DJT. Looks fairly neat if I may say so myself :roll:

    If you haven't got the DJT/XJT yet, you will need to cut away some plastic in the hole for the tx to make it fit, otherwise I haven't made any further modifications to the tx itself (except for removing the antenna, very easy to do). I fiited the bluetooth unit using an existing screw on the main board, but be careful so it doesn't affect the movements of the joysticks.

    Note that the voltage meter is connected to the rx using a single cable only, the ground wire should NOT be connected to the DJT as the rx is already connected to ground. I don't know if this applies for the XJT.

    It's worth both the money and the effort to do it. The mobile tells me (using a nice female voice) every x seconds how much voltage is left. And btw, I would recommend the XJT with less cables to install in the quad.
     
  9. OI Photography

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    Thanks :) I've had a DJT in my T9X ever since I bought it back in Oct and I've loved it ever since, added OpenTx a little while ago as well. I also have a D8R-II XP that I pulled out of my Phantom when I replaced it with the X8R not too long ago...so the voltage meter I was using with it won't connect to the new Rx.

    I really just want to add the Bluetooth module to the Tx so I can use the Android app, been using the little FrSky LCD display screen and it works ok but it won't display all telemetry from an X8R :( Does the Bluetooth module connect to the DJT via the 4-pin data port? I'd love to see any pics of your install/connections with the BT unit.

    Thanks again!
     
  10. st2430

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    Here are a couple of photos that I hope show what I've done.
     

    Attached Files:

  11. st2430

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    I also wish to upload a photo with an inside view of the Tx, but it wont let me. I'll try later to see if it works.
     
  12. st2430

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    It worked when I made it smaller.
     

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  13. OI Photography

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    Awesome, thank you! Looks like that will be my next project. Now I just need to find out if it's possible with the Taranis too.
     
  14. OI Photography

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    Do you happen to have the link for the instructions for connecting the BT module? Is it really just as simple as connecting the leads from the board to the matching external pins on the Tx? And then just bind to it with your phone and run the app?
     
  15. st2430

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    Yes, it's that simple. You get connection drawings from the internet.

    Sent from my HTC One using Tapatalk
     
  16. st2430

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    Search for HC- 05 Bluetooth

    Sent from my HTC One using Tapatalk