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newbie with first scary experiences...

Discussion in 'Phantom 2 Vision + Discussion' started by criopt, Aug 15, 2014.

  1. criopt

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    Hi to all! Nice machine this P2V+. I had my first flights last days and got warm with it. As a Radio/Television engineer I understand most of the tech stuff quite well but this behaviour scared me a bit: After checking gyros and compass values to be in the range, advanced calibrating the compass I had a short flight with some moderate wind gusts. Suddenly the Phantom started slowly shaking left to right while going down. What was that? A bad try rom the gyros to fight against the gust? Today again, but with nearly no wind. I calibrated compass on site, put smartphone 3m away from machine while doing it , waited for atellites and went up. In a height of about 4 meters it started shaking, but after trying to send it slightly up again it stabilised.
    What happens there? In both cases maybe metal could have irritated the compass. In the first case I was hovering about 10m over a metal fencing of 3 by 3m. In second case I had a metalpole of 5m hight and 6cm diameter in a distance of about 1-2meters.

    Well, however I got to learn, hope the learningcurve is not too expensive...

    Cheers from Portugal

    Olaf.
     
  2. Panamon Creel

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    Are you running with or without prop guards?
     
  3. fastsmiles

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    Be sure and do your compass calibration, "dance" away from any metal interference, especially your car. Prop guards can cause problems on descent, if you are using them.
     
  4. smaugnaut

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    If all your calibrations were reading normal why did you do an advanced calibration? Even a basic calibration isn't necessary unless the software says it is.

    A saying here in America is "If it aint broke dont fix it"

    Now to your problem. I would highly recommend you don't get too high off the ground with this issue. Ive read a lot of forums and haven't heard this one yet. I honestly suspect something in the calibration got messed up. Sorry i cant be more help right now but maybe someone else will chime in.

    PS: when calibrating you cannot have the Phantom near anything. The manual states these devices clearly but if i had to do a calibration it would be outside in a field with my laptop lol.
     
  5. N017RW

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    Google 'vortex ring state' (VRS or settling with power).

    Basically you're descending into prop wash/turbulence and it creates a type of stall resulting in loss of lift.
    Lots of info available so no need to be more descriptive at this time.

    Always try to move laterally when descending and not with the wind if possible.

    Prop guards are believed to contribute to this at times where VRS otherwise might not occur.
     
  6. ToThePoint

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    I suspect a vortex from the prop guards but he didn't let us know if he has some on the bird.
     
  7. Panamon Creel

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    Bad compass calibration or magnetic interference will cause difficulty holding position while in GPS Mode but not Shaking/Wobble.
    If it happens during descend it is possibly loss of lift due to VRS.
    If it happens while stationary in the air then it could be something affecting your IMU like prop imbalance for example or a faulty motor/ESC
    Also borderline gain adjustments can cause such issues.
     
  8. criopt

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    Thanks to all of you for your congributions! Well yes indeed, the twomtimws it happened I was flying with propguards.. I did the advanced calibration because the basic calibrarion was greyed out which I found a bit strange. Wel, I have another flight now and will do this without propguards... lets see! :?
     
  9. srandall25

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    I've exhibited this wobble of death a few times since I've been flying the Vision+ when it first came out in April. I've studied many similar reports from others on the same subject matter. Many people jump to the VRS conclusion on this.. which it may very well be... but after my last wobble of death occurred, I noticed a compass error on my phantom after immediately connecting it to the assistance software. I also remembered that I was flying very close to a huge rock side of a mountain... a rock that is very rich in iron... then i remembered another time i had set the phantom on the same type rock as a launching point, and the DJI app telling me of a compass calibration error.. even after doing the compass dance many times... the rock was apparently throwing the compass off. Iron is known to do this. At this point, based on all my experience, I personally believe that a failed compass during flight can indeed cause this wobble of death... and it is also my belief, that a lot of other presumably VRS reports, are actually due to a failed compass or compass interference... I believe what is actually happening is that when the compass is not reporting the correct orientation, the GPS algorithm that keeps the phantom stable at a fixed point, is no longer properly executing the proper flight corrections (with respect to orientation) that is needed to keep the phantom stable at that fixed point. The lack of a proper fixed orientation or compass setting results in these 'jerky' sporadic corrections... causing this rapid oscillation or 'wobble of death' as I call it... I could be dead wrong on this.. but this is my belief based on everything I've personally experienced and read here in the forums.. and trust me.. I've read my share of threads in this forum regarding this subject... Reading your report convinces me even more that compass interference is more than likely the culprit...
     
  10. Double-D

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    Re the basic calibration button greyed out. Try moving or rotating your Phantom while connected. Works for me.
     
  11. Panamon Creel

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    The compass and or GPS have no influence on the basic stabilization of the unit. The stabilization is done via electronic gyros in the IMU, the logic in the controller interpreting the gyros and changing the rpm of the individual props accordingly. The GPS and compass work together for holding positions horizontal, fly to WP and for RTH and that's all.
    Low Gain adjustments can also result in out of control wobbles besides VRS
     
  12. AsiaFlyer

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    Yeah I had the same today setting up my new V+, the advanced option was the only one available but it calibrated quickly, luckily I had several successful flights today, I am using a out the box set up, (no prop guards etc), it flew wonderfully, made me very confident, hand caught it on every flight and even took it out over the ocean(1st time ever flying)
     
  13. smaugnaut

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    Mine is grayed out to sometimes. I dont know why but whenever it is the drone is warm from a flight. I turn it off and let it cool then its not grayed out anymore. Maybe moving it like the op said will work.

    Today i was out flying with no prop guards, winds were 5-10mph, 12 sats full battery on everything and i just hovered at about 15' and did notice a very slight wobble (no oscillation) but i was convinced it was just trying to compensate for the slight wind. I went on to continue my flight for my personal distance record with no problems.

    I wish we could see what was happening with yours. Let us know what happens with your latest flight.
     
  14. srandall25

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    When I say stable.. i'm referring to stable with respect to a fixed position and orientation... The compass and GPS also aid in keeping the phantom stable with respect to position and orientation. As per one definition of stable from dictionary.com .. "having the ability to react to a disturbing force by maintaining or reestablishing position, form, etc." The compass and GPS certainly aid in re-establishing the intended position and orientation

    I believe what is actually happening is that when the compass is not reporting the correct orientation, the GPS algorithm that keeps the phantom stable at a fixed point, is no longer properly executing the proper flight corrections (with respect to orientation) that is needed to keep the phantom stable at that fixed point. The lack of a proper fixed orientation or compass setting results in these 'jerky' sporadic corrections... causing this rapid oscillation or 'wobble of death' as I call it...
     
  15. criopt

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    That gets interresting. Let me describe what happened in the second, nearly crash. I was descending sloowly from a height of about 5m. No wind whatsoever, I watched the video again and again. Then there was a rhytmic movement, left right,left right with a frequency of about one second. While this happens phantom loses height about 1m per second. In this second case it re stabilised for whatever reason. I think I tried to accellerate upwards.
    I know that my ground was a ceiling from an underground parking, with a lot of steel inside for sure. I set up some hundred sat dishes in my life and know how unreliable compasses can be soon as they get close to metal.
    BUT: I am quite sure other drones also use a compass, so: Is this a general rule we are not knowing by hard or is it problematic firmware code that makes compass disturbances so dangerous? Are we not more likely talking of gyro problems? Although gps position jumps could be a scenario as well.
    I think the programmers from dji should read this because of that frequency of about one second. This shows that we are not talking of a value that changes because of interference and stays for a while until it gets back to correct value. What we see are several unsuccessful attempts of the drone to level itself out. Every attempt leads to the next bad angle, not to a leveled state. Also usually if e.g. entire left side of drone is too low firmware will surely try to raise left side, not to lower right side or am I mistaken? So why is it loosing height when trying tolevel the drone out?
    Anyway, I think we are facing a "regelkatastrophe" here. (Hard to translate) This is if you try to level something out and everytime you put far too much or by far not enough.

    I will go back to site with my analog and my digitalcompass and check for anomalies.

    My client wants me to film a lot over water, so I have to be sure not to make mistakes then. I will stay tuned here about this issue.
    I will try to point someone from dji to this thread... lets see if this is possible.
     
  16. Panamon Creel

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    an incorrect compass orientation will not cause oscillation, what it will cause is that the quad will fly slowly in a circle with increasing diameter as it goes. Wobble of death is caused by VRS, too high of a payload, wrong gain adjustments, IMU failures, motor or ESC issues,...etc.
    Sadly the magnetic compass calibration seems to have become the answer to everything when something doesn't seem to go as planned with the quad
     
  17. srandall25

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    That's interesting because I was thinking the same thing about VRS. Every time I've seen a reported wobble and descent issue, VRS seems to have become the answer. I'm only speaking from my own experience. Immediately after experiencing this on two different occasions, I had a reported compass error. And I was flying near rock rich in iron. I don't believe the compass alone is responsible for a violent wobble. I believe it's possible that a compass interference is the source culprit in a series of events involving gps and other flight corrections that rely on a proper compass setting that ultimately leads to such an effect.
     
  18. srandall25

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    This is exactly what I'm speculating on. What you described fits right into my theory. I agree. The compass could be the culprit that software could be programmed to remedy. If you could get the opportunity, it would be interesting if you could put the phantom on that same ground while connected to a PC and assistance software and view the calibration readings as you move it from various points on the ground.
     
  19. criopt

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    Thats a brilliant idea. The spot is nearby and I know exatcly the position where it happened. Although I have to say that yesterday I saw a lot of videos with phantoms in VRS conditions. But all of them have been descending fast, from higher altitudes. I was in both cases in a hovering state and then carefully descending. First crash was at about 7m height, second one about 5m. No reason for a VRS we should think. But yes, in both cases with propguards.
    The last two days I emptied about 6 sets of batteries without propguards and always with a bit of angle when descending. No problems whatsoever until now.
    Tomorrow I will start first time from a vessel on the open Atlantic. Lets hope the Phantom stays dry...
     
  20. Airmotive

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    One thought of something to try....
    Hover just above the ground. As close to the ground as possible without touching it. Ideally, less than one rotorblade length.
    If your aircraft still wobbles while in ground effect, you can eliminate any sort of VRS.

    (Personally, I think VRS gets a lot more blame around here than it should. Ditto for prop guards.)