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GPS fails during flight

Discussion in 'Phantom 2 Discussion' started by wkf94025, May 27, 2014.

  1. wkf94025

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    Several times now I have experienced what seems to be a GPS system failure mid flight. The OSD suddenly shows zero satellites, the flight mode jumps from GPS to ATTI, and the speed indicators are zero'd. I believe the nav diamond also disappears. It happened to me for about the fourth time in several months this morning. First symptom was no longer holding lat/long position, then when I went to correct, I noticed ATTI in the OSD. Once I realized GPS was out, it seemed to fly ATTI mode normally, and with about 10kts wind, was a mild challenge to bring home, but nothing to panic about. I waited in the air a bit to see if the GPS would reboot and find sats again, but no joy. I landed, powered down the P2, then immediately powered it back up on the same battery, and GPS was normal. Quick lock on plenty of sats, then I flew the rest of that battery, and then two more full batteries without incident. The first time this GPS outage happened to me a few months back, I opened the shell and checked for any obvious signs of loose connections, solders, etc. Nothing obvious.

    If this is a problem that a rookie experiences in any degree of wind, I could imagine it being experienced as a "fly away", though in fact it's more of a "drift away". Though apparently in this failure mode it responds just fine to stick input.

    I've concluded this is a shy bug that could show up at any time on any flight, and that I can't always count on HomeLock to be there for me. In such events, I either need to nav home visually or through FPV, or force RTH.

    Silver lining is that it shouldn't toilet-bowl when the GPS is out. :D

    Curious if others have seen your GPS system [only] give out in flight.

    Kelly
     
  2. goldfishrock

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    Did you remove the RF shield coverting the GPS and check the connections to the actual GPS module?

    I would guess the problem is highly likely to be electrical rather than NAZA based. It could be a hairline crack on the GPS board (or mainboard), a dry solder joint or lifted track. Maybe worth taking it apart again and really checking it over. If it's a crack you may find that as it warms up the board expands and 'breaks' a track. Once it cools down again, it works fine.
     
  3. wkf94025

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    I did pull the RF shield and remove the GPS unit from the lid. Fairly thorough inspection, but who knows where the gremlin(s) might still be hiding. Tend to agree it's more likely a physical connection issues than NAZA/firmware bug.

    Kelly
     
  4. ianwood

    ianwood Taco Wrangler
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    It does sound like an intermittent connection. Maybe with the top shell off, connect the GPS, plug it into the Phantom Assistant and check that it is GPS mode and then watch the mode while you wiggle cable around, nudge the connectors, etc. See if it drops to ATTI at any point.
     
  5. N017RW

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    I recently opened my P2 for the second time.

    Whilst I've had no problems I just wanted to take a second look at all the solder, connectors, strain relieving, etc.

    I personally thought the GPS connector into the 'main' PCB was sloppy. Seems to have a lot of side-to-side or tipping motion. Since I'm not sure of how the contacts are designed I added a small piece of tape to the body of the connector to stiffen it up once inserted. It feels more secure and does not move.

    I am NOT saying this is a cause since I have not had an issue but it is worth looking at to see if in other cases it might be a factor.
     
  6. PhantomPhreak

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    I don't have an FPV setup yet. I am curious if you switch it to ATTI with S1 does the IOSD still report GPS data? If no I was thinking it could be a flakey S1. I had to replace mine.

    Sent from my DROID RAZR using Tapatalk
     
  7. wkf94025

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    Thanks for those suggestions gents. In reverse order of suggestion:
    1) my S1 is solid. I use it all the time without issue. When GPS goes out, toggling S1 make no difference; GPS still dead.
    2) I had the same thoughts about the flimsy connection between GPS cable and motherboard. Good idea to shim up. Will do.
    3) Good idea for bench diagnostics of possible causes.

    I will try 3) then 2).

    Kelly
     
  8. N017RW

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    Good point.

    In your example then GPS 'control' should restore immediately once the switch is fiddled with.

    In my example, or similar, it would have to wait for reacquisition to occur since power was lost..
     
  9. wkf94025

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    All symptoms point to power loss to GPS subsystem. No other symptoms in any flight condition over hundreds of flights suggest S1 issue.

    I am curious if GPS subsystem will reboot and reintegrate with NAZA in flight. Easy enough to test on bench. I wouldn't be surprised if NAZA is not coded to allow loss and recovery of rebooted GPS.

    Kelly
     
  10. ianwood

    ianwood Taco Wrangler
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    The GPS unit simply spits out a stream of data and doesn't have any statefull integration with respect to the NAZA. So should it reset mid-flight, the NAZA would go into a non-GPS mode until the GPS data stream resumes.
     
  11. KBurn

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    I had this happen to me yesterday. Almost crashed into the roof of some houses... I didn't realize then but must have suddenly switched to Atti mode and the P2 started to drift... as I was flying over a canal, I simply concentrated on guiding her back when a huge gust took her and sent her almost into what I thought was a fly away situation! The only reason why I knew it was still under control was because I could still send her up...barely! GPS seemed to lock on again and it hovered at height and I could bring her home... it did drift again towards the end.

    Today, I did a pre flight check (at a different location) and after calibration. The P2 lights flickered green and then pulsed green slowly. However, even though the lights stayed this way, my iOSD display on my monitor showed the mode flickering between Atti and GPS! It seemed to stay mostly on Atti but all lights were green! I also saw that I had 7-9 satellites locked on...

    Someone please tell me what's going on? I'm too afraid to fly her now! I used to rely on the green indicator lights and knowing I have at least 7 Sats locked on. Never thought I would need to check the mode as well since green means it's in GPS mode? !

    Please help :(
     
  12. wkf94025

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    I experienced two complete GPS outages tonight during the course of flying three batteries, on a new P2 with H3-3D, iOSD, IRC 600mW VTx, and SpiroNet antenna. I was also packing a Garmin GTU-10. This is a completely new P2 and gimbal than the one that experienced GPS outages last month. Very curious. Wondering if somehow the GTU-10, when it updates position every several minutes, is somehow knocking out the P2 GPS. Thankfully I had FPV in place and was able to visually orient and fly home in ATTI mode. At the time of the first outage, I was 2.5km out, and not excited to have lost Home Lock and Failsafe options.

    Welcome any theories. Can post video from DVR + iOSD overlay later this week. When GPS goes out, # sats remains zero, horizontal speed reads zero, and one needs to fly ATTI by pitch and roll degrees to get a sense of speed and orientation. Thank God for FPV in these situations.

    Kelly