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IMU/Compass calibration, EMI and flyaways

Discussion in 'General Discussion' started by mroberts, Jul 23, 2013.

  1. mroberts

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    Do people do a full advanced re-calibration and compass cal when they add new electronics? Reading through my PPL book, it refers to the compass calibration being dependent on which electronics are turned on at the time. That seems to indicate that it might be worth making sure everything is on when you do both the IMU cal and the compass cal.

    I'm reasonably confident that all the chinese electronics we're putting on these things doesn't go through the same EMI/EMC testing as hardware for full size aircraft!
     
  2. howardmaryon

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    With the phantom, frequent recalibrates and compass resets are a way of life if you want to avoid flyaways. Better to spend 10 mins checking the naza and compass, than 5 hours trying to find where it landed or crashed.......
     
  3. martcerv

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    Great advice right there.
     
  4. Sac D

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    That's for sure! Test and calibrate your Phantom while your batteries are charging or something, guys. Don't be in too big a hurry to get in the air.
     
  5. Travis McKnee

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    The pilot who did 25 tips for the Phantom on YouTube, said on his video that it is only necessary to recalibrate the compass every couple of weeks or so, but is the advise faulty? Should you recalibrate your compass every flight? Or, at least every day you're flying even if it's the same location? How susceptible is the compass to being compromised, say in being transported? I think the issue of the integrity of the compass is something that needs to be explained by the manufcaturer in depth.

    Also, regarding flyaways, is there any consensus on the advisability of having a GPS tracking capability, such as the Garmin? GPS on the phantom now seems only capable of bringing the bird back to its starting point and returning it to that position. Why couldn't it be used to locate a downed flyaway, as in the "find my iPhone" feature on that gadjet?
     
  6. Northwest_Scene

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    Ive recently experienced a true fly away but luckily this was flying low and fairly close to me as shown on my video footage. Regardless of all the pre-flight check ups and calibrations of the compass and IMU's, there are still a very good chance that the drone itself will lose control totally. Im very meticulous to my equipment as they are a hefty chunk of cash flying around so I follow all instructions down to the very last detail. I just had a DJI rep explain and ADMIT to me in clear voice that there are stronger frequences everywhere that interfere or is causing drones completely uncontrollable And yet the company as whole still doesnt adress the issue or admit that there is a flaw in the systems and should be dealt it immedietly before SOMETHING or SOMEONE causes a major ACCIDENT involving DRONES and there goes STRICTER RULES or worse BANNED from flying in public airspace etc.
     
  7. UrAwFuL

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    I think I do more flight checks than what a space shuttle does.
     
  8. Northwest_Scene

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    same boat here, but it still wasnt enough to prevent the craSH
     
  9. Hawkeye 1

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    Didn't keep mine from flying away and I had recalibrated not two hours before. The DJI tech made the same admission to me...that some stronger signal was taking control of these things and causing this!
     
  10. Miika

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    What I've noticed is that many of the people who have had an fly-away have said that they relclibrate the IMU all the time and the compass aswell. I do compass calibration if I'm travelling into a new location hundreds of kilometers away and IMU calibration only SOMETIMES.

    What tells you that you need to calibrate and recalibrate your Phantom all the time? If you dont bump into things or crash with your Phantom you should be good to go all the time without recalibrations. Wheres the proof that it helps as people doing this have had multiple fly-aways.
     
  11. EMCSQUAR

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    Calibrations are good and keep your Phantom stable but it's not the automatic deterrent to a fly away. If you get hit with a strong enough RF signal it can alter your flight no matter how many times you calibrate. If you want to test this theory - put your Phantom up to say 20ft - take your GoPro wifi remote and flip it on once. It doesn't matter if your GoPro is on or not - just turn on the little remote control that comes with most GoPros. This will still be close enough to control but you'll see what unstable flight is.
     
  12. Miika

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    If you haven bumped or crashed your Phantom, everything should be fine. If the compass mod value is around 1500 and you havent travelled a long distance before your previous flight, there should be no need for compass calibration. For an example if your calibrating your compass out in the field without a computer, you dont know if the compass calibration actually made any difference or if it even actually worked. You get a succesfull compass calibration even if your compass is way off. You might have a bad compass calibration and not know about it until you connect your Phantom to your computer.

    DJI doesnt advice people to recalibrate everything all the time (please correct me if I'm wrong). So where does this idea of relicalibrating just to be sure comes from? If theres no evidence that its good for your Phantom (as people calibrating their Phantoms all the time also have fly-aways).

    IMU needs to be warmed up for IMU calibration to be succesful and if its over heated the calibration doesnt work. What I've noticed is that the Naza Assistant works in mysterious ways. Sometimes it tells me that my Phantoms IMU is too hot (or what ever) and it proceeds to calibrate it, even though it just asked me to unplug my Phantom. Sometimes it ask me to wait for the warm-up etc. I bet there are glitches in the Assistant software too. So in my opinion its wiser to recalibrate the IMU as less as possible (unless you bump or crash). And only check the compass reading from assistant for a good mod value etc (unless you have travelled).

    What if theres a glitch in Naza assitant that causes something that we know nothing about during the IMU calibration? Theres possibly glitches in the Nazas firmware/software itself. The more you calibrate the more the chance of something going wrong increases. If it aint broke (Phantom works as it should) dont fix it. I'm not sure if this is just a feeling, but my Asus T100 transformerbook worked flawlessly, but I saw that they had newer bios for it. Upgraded and started having minor issues that I believe I didnt have before. If it aint broke, think about before fixing it.
     
  13. Miika

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    To clarify my point its hard to believe that Phantom could become unresponsive and suddenly just take-off and fly into the abyss. I've heard about case(s) where Naza controller (in non-Phantom quad) had detached from the body of the quad. In this case Naza tries to level the quad because its getting faulty infromation from the gyro and this is something that ends up in a fly-away. The Phantom just keeps flying. I assume that broken gyro causing faulty readings could also end up in a same situation.

    Phantom in a need of calibration doesnt fly too well, but it doesnt cause the Phantom to FLY-AWAY. I've lost one Phantom with 1200€ in it. And I honestly would like to find the reason of these fly-aways, but as said Phantom in a need of calibration doesnt go crazy. So

    Fly-away
    1. Phantom becomes unresponsive (might receive RC input at some point or points)
    2. Flies away

    So how could bad calibration cause RC control blackout? You can turn your RC into altitude or manual mode to make sure your Phantom isnt taking any readings from gps, compass, barometer or gyro.
     
  14. F6Rider

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    I only calibrate my compass when I fly in a different location some distance away from my normal field. I have NEVER done a IMU calibration in 55 flights because the assistant is telling me it is not needed and I can skip it. As my bird fly's just fine I do not want to take the chance of introducing a glitch into the system as long as it is working well. As a retired Helicopter Tech Inspector (military) I know the importance of pre-flight checks and PM (preventative Maintenance) so I do them. I never lift off unless everything is in the green, and so far have had no issues (knock-knock), and I wish to keep it that way. Too much maintenance can be just as bad as too little. Doing unnecessary <electronic> calibrations increases the chances of introducing a variant into the system that can lead to incorrect information, or system lock up. I am not suggesting that this is the underlying cause of fly aways but could be a contributing factor.
    One point.... I fly in a sports park a lot and there is a huge cell installation on one of the light poles, in 20 or so flights there I have never experienced any interference from it, not even to my video link. After reading all of the cautionary comments about this I now fly in another part of the park, better safe than sorry.
     
  15. ianwood

    ianwood Taco Wrangler
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    To answer the specific question posed by the OP, it's similar to a compass on a boat or plane. And because everything on the Phantom is within close proximity of the compass, you want to calibrate the compass anytime you change the physical configuration of the Phantom and especially when adding/removing anything electronic. Anything that will be powered and active during flight should be powered and active when you do it.