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Rotating The Compass (and other bad ideas)

Discussion in 'Phantom 2 Discussion' started by ianwood, May 21, 2014.

  1. ianwood

    ianwood Taco Wrangler
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    This thread is dedicated to the discussion of rotating the compass. If you want to talk about rotating the compass, do so here and not in threads dedicated to getting DJI to fix the declination defect.

    (If you want to talk about fixing the declination defect properly, go here: viewtopic.php?f=19&t=10317)

    To get you started, some reasons why you might consider rotating the compass:

    • You live in Northern Canada or New Zealand and you have crazy TBE and hooking and nothing to lose.
    • You don't live in Northern Canada or New Zealand and like to experiment despite the abundance of evidence to the contrary.
    • You want to perform data driven tests to help study the declination issue.

    And some reasons, why you wouldn't want to rotate the compass:

    • DJI does not recommend rotating the compass on the P2.
    • Just because it works on another platform doesn't mean it will work on this one.
    • The Naza will over-correct and you will end up hooking in the other direction.
    • The compass is meant to be aligned with the vehicle. As a sensor, it will return inaccurate data when rotated.
    • You cannot be certain that you're not introducing compass errors that can result in a flyaway.
    • The compass is not physically designed to rotate easily. Screws back out, compass comes loose. Goodbye Phantom.
    • A handful of people if not more will magnetize their compass by using a magnetic tipped screw driver.
    • It's a half-baked workaround that doesn't really work and you want a real fix from DJI.

    Tests conducted (Los Angeles, 12 degrees declination):

    • With no rotation, I get hooking that slowly straightens up after 7 or so minutes.
    • With the compass rotated nearly double the declination, I get straight flight that slowly turns into hooking after 7 or so minutes.
    • With the compass rotated by only the declination, I get lesser hooks in one direction for a few minutes, straight flight in the middle, and then lesser hooks in the other direction.
     
  2. sar104

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    Well played. With such an inviting topic name it will be interesting to see if anyone posts on the subject.
     
  3. Andy T

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    Not likely
     
  4. golgotha

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    I don't like rotating the compass as much as Ianwood does.

    Sent from my Nexus 7 using Tapatalk
     
  5. Andy T

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    Well if DJI comes up with a solution involving rotating the compass like they did with the NAZA M version or whatever it is called then I would gladly implement it. To not think that it is an option seems ridiculous as it was the way the declination issue was addressed in the past. Seems the conversation has pretty much broken down here.
     
  6. sar104

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    I think the issue is to keep the pressure on DJI to find a solution, whatever that might be, rather than dilute the message in the main thread by debating whether a rather inelegant fix (if only because the compass is not easily rotated) is actually working, or how well it is working.
     
  7. tom3holer

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    Ianwood,

    You had repeatedly asked to start a new thread if one wanted to talk about compass rotation to correct the related issues so I did earlier to only to see you started one also sometime later.

    I applaud your efforts to get DJI to correct the problem and even sent you a PM in that regard a week ago but you did not respond.

    The point is that we all would hope that DJI would resolve the issue The fact their Naza line has had this problem since the beginning, I believe, and they recommend rotating the compass to correct it makes me believe it is not a fix they deem necessary or involves a lot more coding than they care to do.

    I simply wanted to report my success at trying it on two different P2's in my area of 15deg.

    My first P2, I flew many flights after getting the right offset and never found it to overcorrect. I just flew as it should.
    I did make sure the compass was fixed so as not to rotate and did use fresh locktite on the screws.

    Perhaps it is my area, not sure but will be doing more flying/testing.

    Tom
     
  8. Andy T

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    Awsome. I'm probably going to try it too. I appreciate your input whether someone thinks it was inappropriate or not. I feel it is valuable information and would not hesitate to pass it on to Dji as your fix to an intolerable problem in their design
     
  9. ianwood

    ianwood Taco Wrangler
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    Apologies. I didn't see your thread when I started this one. This was a knee-jerk reaction to what seemed like yet another segue into a whole bunch of "just rotate the compass" posts and I wanted to nip it in the bud.

    Anyway, I have no issue with people rotating their compasses as a workaround as long as they understand all the caveats associated with it. If I were in NZ or northern Canada, I'd probably do it myself. And I have done it. Several times. I found that it gives me very mixed results. And now that I've flown in a low declination area and experienced truly straight flight, I am even more convinced that rotating the compass is a poor workaround.

    Most importantly, it is not a solution. And I don't want people to confuse it as such.

    It's possible the P2 deals with declination exactly the same way as all other DJI FCs. But then, why not design a means of rotating the compass like the others? I suppose they might have thought no one would care. But from all that I've seen so far, the P2 doesn't deal with declination like the others. It appears to be applying an offset for declination and it appears to be applying it backwards. Even in Chicago, I had a course lock deviation of +8 degrees which is exactly double the local declination.

    Bottom line, I want straight flight no matter where I am. Others want it too. If DJI doesn't deliver it, we're going to make a lot of noise. If people want to rotate their compass in the meantime, that's fine by me.
     
  10. sar104

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    Agreed, and I don't think there is any question that the Phantom FC is attempting a correction - the CL error of twice the local declination is unambiguous evidence both of a correction and of FC awareness of the local declination.
     
  11. KG4MXV

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    I just wonder why they separated the compass from the GPS PCB in the P2's

    I wonder if it was because of interference issues with the other electronics.
     
  12. ElGuano

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    That's right. Normally the GPS puck is on a mast to be positioned far above the battery and other electronics; it was originally designed specifically to isolate the compass from interference. The Phantom is a smaller integrated package and they didn't want to have a mast sticking over the top, so the puck was placed under the shell just a few cm from all the other electronics (Naza, PDB, ESCs, RX, battery); because of this they separated the compass and isolated it by placing it on the leg.
     
  13. tom3holer

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    Its not just the Phantom, the Naza-M v2 that was in my Discovery Pro also had to have the "Puck" rotated about twice the Dec. This is common knowledge among Naza-M owners. It has to be way more than just changing the sign of the dec table otherwise with all of their controllers effected, sans the top of the line A2, they would have corrected it by now.


    Tom
     
  14. ianwood

    ianwood Taco Wrangler
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    So regular Naza users don't rotate them just to the local declination and instead use double the declination? Does it overcorrect and end up hooking the other way half way through the flight? Is course lock off by double the declination as well? The P1 doesn't do this or at least I've been told by a number of people the P1 doesn't behave the same way.

    I can't believe people would pay that kind of money for a flight controller only to have it not fly straight in many parts of the world. And it's such a simple thing to implement.
     
  15. nzvideoguys

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  16. ianwood

    ianwood Taco Wrangler
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    I am not going to be shy with my opinion. I think rotating the compass is a bad idea except in extreme cases (NZ being one of them). I've laid out the facts (or at least what is known at this point) for good and for bad at the top of this thread. I am not saying people shouldn't do it. Everyone is entitled to make their own choice.

    But when I create a thread to have a focused discussion on getting a solution from DJI, I don't want to have to debate rotating the compass every 5 pages like a broken record. It takes away from my effort and dilutes the focus. I can't guarantee DJI will do something about it but we've at least got their attention. I'll be damned if I don't make an effort to get them to fix it.

    And I've never said it would be simple for them to fix it. I've said that adjusting for declination is a simple solution. Part of the issue is likely that they've already included the functionality but didn't do it properly. That likely makes it less straightforward.
     
  17. nzvideoguys

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    Well, I'm willing to do whatever is required to put pressure on DJI to get it solved. What do you suggest?
     
  18. Andy T

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    @nzvideoguys was that you that posted a comment to https://www.facebook.com/DJIglobal If so BRAVO! Facebook is awesome to get things done. We have to go there and like the posts that people are placing there and if there is not a post about the issue near the top of the page, make one. I also posted to my dealers Facebook to encourage him to put some pressure on DJI. He replied instantly that he will talk to them.
     
  19. Andy T

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    If DJI decided to redesign the leg and compass so it can be rotated to solve this issue I would be extatic even if I had to pay for it. A compass and a leg is 20 dollars. To say that is an invalid argument and ban it from you discussion is as you would call it a "bad idea"
    Nevertheless, thanks for getting this whole discussion going and doing most of the work regarding the issue. We don't have to agree on everything though.
     
  20. ianwood

    ianwood Taco Wrangler
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    You and me both. If only it solved the problem. Unfortunately, the following issues remain:

    • Just because it works on another platform doesn't mean it works on this one.
    • The Naza will over-correct and you will end up hooking in the other direction.
    • The compass is meant to be aligned with the vehicle. As a sensor, it will return inaccurate data when rotated.
    • You cannot be certain that you're not introducing compass errors that can result in a flyaway.
    It's like having a broken leg and instead of having surgery to fix it, you just slap two pieces of wood to your leg. You might be able to walk, but it's going to suck.

    If rotating the compass actually made my Phantom fly straight for the full flight, my compass would be rotated and I would be suggesting everyone do it until DJI fixes the problem. All the tests that I have done show it overcorrects:

    • With no rotation, I get hooking that slowly straightens up after 7 or so minutes.
    • With the compass rotated nearly double the declination, I get straight flight that slowly turns into hooking after 7 or so minutes.
    • With the compass rotated by only the declination, I get lesser hooks in one direction for a few minutes, straight flight in the middle, and then lesser hooks in the other direction.
    Others have made similar observations.

    If the conversation occurred once in that thread, I would agree but it turns up like groundhog day. Explaining the same thing over and over gets old quickly and takes away from the purpose of the thread. I made it clear from the very first post that I wanted to discuss fixing the problem and not looking at kludgy workarounds like rotating the compass.