3DR Iris GPS HDOP

The Iris will not arm itself with DOP above 2.0, even with 9 sats and "3D GPS" displayed on telemetry. The screen reports high H (horizontal) DOP, possibly because I am surrounded by hills. Can the DOP threshold be increased?

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  • Even I have found the same issue is HDOP at 2.5 (>2.5 only not less than that) but instead of all this comment, I have tried one thing that is I have checked the battery voltage it is less than 3.0 Volt so you can charge either you can replace the mercury cell it is easily available in the market :) 

    Happy Flying :)

  • I am also having random GPS issues on the IRIS. One day it works great although I never get an HDOP less than 2. 

    The next day I only 5 to 6 satellites with HDOP of 4 to 6. It can site there for 30 minutes and not improve. This is in exactly the same tree free field that I was in the day before when it all worked great. Multiple reboots of the Pixhawk does not help. 

    I would say this has been happening about 1 in 5 flight days but lately getting worse. This past weekend I had 2 days in a row with only 5 to 6 sats and hdop of 4 to 6. When this is happening it also can get multiple GPS failure warnings. I've tried getting it up to 50 or 60 ft alt to improve the signal but nothing helps. Also, my Garmin car GPS works perfect on these days with normal DOP.

    mp

    • Ditto. Took an hour to get the green light today.

      • Let me apologize. I searched for this thread today and couldn't find it so I started another one. My post and link to the thread is below.

        other thread

        Looking for some other IRIS flyers that may be having poor GPS performance.

        Only about 1 in 7 flights do I get HDOP lower than 3. After about 40 flights I can only remember it getting below 2 a couple of times. One day it's in the low 2's and over half the time its 3.5 to 5 and getting repeated GPS failure alarms.

        Is this normal? With that issue and the alt hold issue where any horizontal flight causes a big drop in altitude I can't really do much beyond fly around in stabilize. I think I can tune the alt hold issue thought.

        mp

  • Yes you can change the HDOP threshold higher in mission planner (MP)

    Config/Tuning --> Full Parameter List and look for the GPS_HDOP_GOOD command. (Click "find" and type "gps" it is much easier to find the command like this)

    It is set to 200 by default which means 2.00

    I have mine set to 250 which is 2.50 because sometimes my Hdop can get into 2.3, 2.2, 2.1 etc and still hold a loiter position very well...meaning the rest of the navigational flight modes will work fine.

    I would not set it higher than 2.5 though. Over 2.7 or 2.8 you should not attempt any navigational commands such as Loiter, RTl, Auto, Circle etc.

    Without a good gps lock you should only fly in Stabilize mode.

  • Yes, I'm having these issues as well. I often have an HDop of 9.
  • Developer

    Hope this helps.

    • You can take off in STAB with no GPS lock HDOP does not matter. = Green Light
    • You can take off in Loiter with GPS Lock, HDOP < 200cm = Green Light
    • You can take off in Alt Hold with no GPS Lock HDOP does not matter = Green Light.

    AltHold and Loiter are Fly-By-Wire modes, no direct link to throttle. Above 50% on the stick is the rate of height gain, below 50% gain is the rate of descend

    You can get 7 or 8 satellites indoors, but HDOP will be poor, as the GPS sat signals are reflected through the window. It known as mutli-pathing. If you get a HDOP < 200cm indoors its probably still incorrect (HDOP is indicative and not perfect, HDOP is calculated on the uBLOX GPS unit, not the Pixhawk)

    My two suggestions would be to go outside and repeat the test away from the buildings and trees. Then see what happens with a take-off in Alt-Hold, as suggested in the manual, Then swicth to loiter. As long as you are not too near buildings and have a good view of the sky, it will be as expected.

    Good luck, and let me know how it goes.

    • 3702480896?profile=original

      Hello,

      I'm flying with a VrBrain (Italian variation of PixHawk) with 3DR uBlock LEA6 GPS. With 9 to 10 sats I have a HDOP below 2.

      GPS antenna is glued on the frame close to the VrBrain.

      Marc

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