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GPS Mode and the Compass J Hook

Discussion in 'Phantom 2 Discussion' started by ianwood, Mar 2, 2014.

  1. ianwood

    ianwood Taco Wrangler
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    Who else gets this J hook effect in GPS mode? I am noticing it more and more as I get better at flying this thing. It happens most when first setting off but is still there even a couple of minutes into the flight. It happens even with a fresh compass and IMU calibration. ATTI is perfectly straight so it has to be something with the way the GPS and compass are interacting. I have noticed that switching to ATTI and then back to GPS makes it less pronounced.

    It's always to the left going forward and to the right going in reverse. The hook happens when you let go of the stick. Also, there is a slight but noticeable deviation in the what is actually forward. Forward stick moves the Phantom about 5 to 10 degrees to the left of the actual forward direction. I am wondering if this has something to do with magnetic declination or flexing of the landing gear or even the direction you turn the Phantom doing the compass dance.

    [​IMG]

    Here's a video that someone else made of the same issue:

    [youtube]http://www.youtube.com/watch?v=DHuzmBxej5M[/youtube]
     
  2. goldfishrock

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    Oooo.... that's a strange one. I've thought for a while that my P2 and a slight tendancy to creep left in straight flight from time to time, although it's not quite as pronounced as what you are describing. I wonder if it's linked....
     
  3. ianwood

    ianwood Taco Wrangler
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    So, I found a workaround but I haven't figured out what is going on yet. Need someone to replicate what I've discovered:

    Start in GPS as normal. Fly out hard forward about 20-30ft and then let go. See if it hooks left (or right). Do the same in reverse. It should hook in the opposite direction. Switch to ATTI, fly for a minute, switch back to GPS and repeat the same test. Any hook that occurred before should be totally gone and the Phantom should fly totally straight without any hook.

    Bizarre. I can't figure out what is doing this. I wonder if there is a bug in the Naza related to adjusting the compass heading for magnetic declination which it is supposed to do automatically using the GPS location. I wonder if it would fly perfectly straight if I shimmed my compass to point it 12 degrees to starboard.
     
  4. Driffill

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    It's because of the magnetic declination of your local area!

    It's been mentioned plenty of times on this forum, and others. Non phantom Naza users can turn the GPS puck to compensate for it, but with the compass mounted to the leg of the phantom, you need to sort out some way to slightly adjust the position of the compass . . .

    Be sure to let us know how it goes!
     
  5. ianwood

    ianwood Taco Wrangler
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    That's why I think it's a bug in the firmware. From what I understand, the firmware is supposed to adjust the compass heading for declination based on GPS location. And it seems to do it, but only after I switch to ATTI mode and then back to GPS. Note, I get no toilet bowl at all when hovering, ever.
     
  6. GMANNZ

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    I experience same on my P2V .... have been wondering if is motor issues (which I replaced today, will see) ..... when testing for this drift I did find it was always bad with "speed" ... so I slowed down and decided to learn better control of craft which has helped when going full noise and then need to control it back ... will test with new motor and compass I replaced today, If If get no joy, ... I will try your GPS mode, Atti mode, GPS mode swithing and see if any changes happen for me >>?? . ... weather is crap here today so might be a couple.
     
  7. GMANNZ

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  8. ianwood

    ianwood Taco Wrangler
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    Cross posting this here to collect more data from our P2V cousins.
     
  9. dbot3000

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    Same thing is happening to me with 2 different, new Phantom 2's (not Vision). I just posted a detailed description here:

    viewtopic.php?f=19&t=9492

    But it's the same as the OP described. I'll try the GPS-ATTI-GPS trick on my next flight (hopefully tomorrow) and report back.

    Best,
     
  10. shartlza

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    The same thing is happening to mine as well and this is on a naked Phantom 2. It seem as though it is really bad in the first few minutes of flying. Also i have noticed if it is at a higher altitude it is maybe a little better, but that could just seem that way because movements don't seem so noticable higher up. I did try flying in Atti mode for awhile and it flew perfectly straight, then went back to GPS mode to see if it fixed it. It may have fixed it a bit but it did still seem to drift to the left and then hooking more after letting off the stick. I really hope this is a software thing and it gets fixed with the next firware update. If someone has a good solve please let us know.
     
  11. ianwood

    ianwood Taco Wrangler
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    Good stuff. I see you're also in Southern California where the magnetic declination is about 12 degrees from true North. That's three of us in SoCal so far who've noticed this issue and I bet there's more. And I would like to see some Northeasterners chime in where the declination runs from -10 to -18 depending on how far North you get. If I am correct about this bug, their Phantoms should be hooking the to the right as opposed to the left.

    World Magnetic Model

    I did some further investigation today. I already figured out that switching to ATTI and flying for a bit will fix the J hook issue in GPS mode. Today I figured out that it does not fix course lock. Course lock is distinctly left of forward by what seems like more than 12 degrees. Also, I calibrated the compass by turning it counter-clockwise this time. I read a post elsewhere that this had fixed a deviation issue with a P1. No difference in my case.
     
  12. shartlza

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    Make that four of us. I am in Orange County and my declination is -12.
     
  13. ianwood

    ianwood Taco Wrangler
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    So just to confirm, you're getting the J hook described above?
     
  14. shartlza

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    Yep, i posted about 3 post back. It seems to slightly go left, then when i let go of the stick it hooks pretty good to the left.
     
  15. shartlza

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    So just a quick update. I went for a full flight today and this is what I learned. First minute of flight was making sure everything was good. Then I took her up at a good altitude and did a full forward and got the drift and hook really bad, so I landed it and calibrated compass (did not do before flight because fly in same spot daily). Took her back up and went full forward and still drifted to the left, but not as bad (only been flying 5 min). Then flipped to Attitude mode and flew perfectly straight for a few passes and then went back to GPS mode and left drift was still slightly there, but only a slight left hook after letting off sticks. Then after about 10 min of total flight time and doing all these things all was good. It flew straight in GPS and when letting off stick stayed straight. Overall it looks like after time the symtoms go away and doing the Attitude mode switch, then back to GPS speeds up the fix. It would be nice if it would be fine from take off!!
     
  16. Madkeen

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    Yes, has this J hook issue today. Haven't tried anything to fix it.

    Seems to be in first fe minutes of flight.

    I am in Brisbane Australia. So doubt it is a location issue
     
  17. ianwood

    ianwood Taco Wrangler
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    As it happens, Brisbane has the same magnetic declination as Southern California. I will add you to the list. Research continues. My next step is to try shimming the compass and see what results I get.
     
  18. Xrover

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    I'm in Los Angeles. I Have the exact same J Hook problem as described. Mine would even pull up while hooking to the left in FWD flight. I had it flown by an experienced Quad guy from the place I bought it. He was dumbfounded. He definitely said there was a prob. He even replaced the compass with no difference. We called DJI Tech support and was lucky enough to only have to wait on hold for 45 minutes to speak with someone. The end result of the phone call was to send it in to be checked out and repaired if a prob. was found. I only had it for a month. I managed to get the dealer to replace it with a new one. (After i paid him $100 dollars) The new one still does it but not so bad. It still has a slight drift to the left in fwd. and drift to the right in rev. The longer i fly it during the same session, the better it gets' I only got the P2 to shoot video for work so any drift makes the footage worthless.

    Just as bad if not worse is THE DAMM YAWing back and forth when trying to do a tracking shot in a straight line.
    ATTi mode helps with straighter tracking and i have yet been able to get any gain settings to minimize the yawing. That's killing most of my shots..

    As a side note to the Magnetic Declination. Los Angeles area is +12 degrees (east) So what!! We have not told the P2 to travel either True North or Magnetic North, only follow a straight line!! The problem I think comes from DJI's programming the NAZA to decipher the GPS information to be an assumed a 0 Degree Magnetic North and not a True North which would then include the Magnetic Deviation for the particular area being flown. Most GPS Map systems will first want you to select or confirm your current location... We don't have that option. If we did, then the GPS info could be calibrated with the compass and the 2 would be on the same page..

    Just my thoughts.
     
  19. ianwood

    ianwood Taco Wrangler
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    Well, Naza users that have the GPS and compass in one unit have to rotate the puck to adjust for declination. It seems we have been given no such provision. Why there isn't a magnetic declination lookup table in the Naza that automatically compensates is beyond me. I am going to hunt down a non-magnetic Phillips head driver in my workshop tomorrow and shim the compass so that it is pointing 12 degrees to the right. Will report back tomorrow.
     
  20. Xrover

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    I'm interested to here how that works out..