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PV2+ Flyaways, GPS interference from camera subsystem

Discussion in 'Phantom 2 Vision + Discussion' started by lizard, Jun 3, 2014.

  1. lizard

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    Hi everyone,
    took my child's P2V+ to our EMC lab to see more closely what is going on with this baby. Beyond the issues with the gimbal control loops and auto-tuning algorithm which are leading to occasional jello, we found very serious issues with the PV2+ electronics, namely EMC issues.
    RF radiation from the H.264 encoder, which is based on the TI DaVinci chip with external SDRAM memory placed in very poor shielding enclosure causes strong interference with the GPS reception. This interference is so strong, that in the place where 22 satellites are perfectly usable with excellent clean signal providing fast and precise 3D fix with excellent HDOP, PV2+ hardly gets 5 or in best case 6 satellites. Even worse, as soon as you place reference receiver antenna nearby active PV2+, S/N (signal to noise ratio) drops immediately and tracking of weaker satellites is lost immediately.
    Implications of this are much more serious: in the situation of any ionospheric or solar winds disturbances, where properly designed system locks easily to enough satellites to get 3D solution, P2V+ loses the fix completely. Any time, without any warning. The situation is probably even worse with PV2, but this one was not tested.
    If you had any flyway crashes or GPS was unable to lock sometimes or any similar GPS related issues, call DJI for responsibility now!
    DJI shall face these facts, take the responsibility, completely change their engineering procedures and completely redesign their hobby line products in order to remove all these gross negligence engineering faults. I'm curious how well are their much more expensive pro-level products designed. I'm skeptical.
     
  2. xgeek

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    Interesting findings.

    I thought the maximum best case visible GPS satellite count was 16?. How was you picking up 22?
     
  3. BlackTracer

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    OK great observation. So what is it we need to shield to get more satellites and stop the GPS interference? We are not going to be sending our birds to DJI to have them install the shielding. What can we do about it DIY?
     
  4. lizard

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    Unfortunately there is no easy DIY fix. Housing is made from anodized aluminum and there was zero care from DJI's engineering to assure proper RF interconnects to avoid radiation. Another chapter is the board level RF EMC behavior of the camera subsystem, which could be not easily fix due to many cables coming in and out to the camera subsystem. From a point of view of professional mixed system (RF/Digital) PV2+ design was completely screwed by DJI engineering. Even if PV2+ passed FCC approval, system level EMC compatibility is hugely severed.
    Most funny thing we found the labels from the integrated circuits were removed (sanded out, shamelessly low-tech). Holy crap, did DJI ever heard about all these Chinese reverse engineering service outlets? They will dissolve IC molded epoxy, identify all chips, reverse engineer whole PCB and schematics and even read out protected flash memories content for like few tenths k$ for medium complexity board.
     
  5. Mori55

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    On my F450 I had such bad interference with my mobius action cam I couldn't get good sat lock I even copper shielded the gps puck.
    I moved the camera as far as I could from the gps puck as possible. Still had problems. I do know after one of the firmware updates it got better. But still didn't great sat lock.
     
  6. beachvision

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    CAn we use any of this data to work with DJI to get ou investments properly fixed? I have to imagine even a few more satellites and a little less interference would prevent the majority of fly aways. Wondering if the new camera gimble has alot to do with interference as I dont remember hearing about this many flyaway issues with P2V. I experienced loss of GPS lock at 100 ft up while flying last night. Had 7 satellites most of the flight and suddenly switched to yellow flashing then abck to green then back to yellow.
    Any info you can give us to contact DJI would be helpful!
     
  7. lizard

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    I'm 100% sure DJI and their responsible engineering teams with their managers are very well aware of all issues. This is actually the gamble about the production cost. While it is easy to make it (the product, in this case Phantom Vision 2 plus) perfect at given production cost, to make it perfect for lower cost will need much more engineering effort, experience, knowledge, time and long term investments.

    It is also very easy for any manufacturer to offload all product issues from engineering to customer. DJI is prime example of it. Fair game? Maybe acceptable for first year startup and something much less delicate than aircraft.

    As DJI knows very well about all issues, they have no reason to listen to their customers. They already know. And hope they will simply buy another model in next 6 months, hoping for better experience.

    Isn't it strange feeling being a sponsor of the company who actually do not care about their customers?
     
  8. offtosleep

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    Than you so much for sharing this information!!! This would completely explain my flyaway and makes me feel a ton better. I can feel much better telling the naysayers to shove it up their asses!
     
  9. offtosleep

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    TWhat time do you think you'll be here today
     
  10. lizard

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    Well, I'm definitely not on the DJI payroll, but I can distinguish well done engineering from junk.
    Yet there are many people perfectly happy with DJI products, and some who don't.
     
  11. tizzl10

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    I'd like to know how you can say that one place on this earth can one receive 22 gps satellite signals? that is impossible.
     
  12. Phantom_Menace66

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    This is all very concerning. My first P2V+ fell out of the sky, in my opinion for no apparent reason & DJI basically blamed pilot error. I began to wonder if I had fouled up somehow, even thoug I was sure I hadn't. Anyway I bought another one which has not yet been off the ground since I got it a week ago... After reading all this and other posts, it will remain grounded until something is done about it. I'm not losing another $1500
    Surely, if DJI are knowingly selling faulty units they are liable? Of course, proving it is another matter.

    I'm not impressed
     
  13. cougar

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    I read this with interest and believe this is from a legit source, but would very much like have some credentials and identifications from the person making these claims.
    If so there can be questions asked to DJI, and if some scientific proof can be submitted as well would be even better.
    Sorry to say, but without any official test documentation this is nothing more then some anonymous poster making claims
     
  14. Dirty Bird

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    I'd also be interested in how many units were subjected to the testing procedure?
     
  15. HunterSK

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    I agree with the above, I work in engineering and without hard facts you don't know what to believe.

    Could lizard (or anyone) please provide some evidence and testing results to substantiate this?

    We need some hard evidence and an understanding on the testing method.
     
  16. povlhp

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    Bad GPS fix or loss of GPS should never cause a fly-away.

    If GPS HDOP goes above a certain value, it should switch to ATTI (and it does ? Or is it only # of satellites ?). In that case wind alone will be able to move it. No fly away.

    And Coming Home should be disabled when HDOP above some value. Not sure if implemented. And it would hover an ATTI mode, until battery causes landing.

    As I see it, GPS noise should not be a problem. Only false signals (should be keyed for the specific receiver ? - or maybe they shipped many with same key ?) should be able to trigger fly-away.

    Even a bad compass should be detectable by the GPS, and can be corrected by flying 2xHDOP or more in direction X, and looking at new pos.
     
  17. DrJoe

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    I don't expect a full on lab effort on multiple samples, and I do appreciate the OP's efforts. At the very least, his son's particular craft had bad engineering and sheilding.

    I call into question the GPS #. You can see a maximum of 16 GPS satellites in any hemisphere. if you see more, they are from another GNSS provider like GLONASS (or in Europe sometimes 2 EGNOS Satellites).
    GPS Satellites have PRN number 1-32, that way you can distinguish them from GLONASS (if you have receiver diagnostics).

    I have stated many times on this board that I feel flyaways are due to bad gps data and the lack of knowledge of how IOC works or how to utilize ATTI or manual mode. With bad GPS, the Phantom should be quite controllable with ATTI or manual mode. Second cause is bad motor/ESC/prop tip fracture. Third is that the electronics/connections just so happen to "**** the bed". But most are pure operator error.

    DJI should provide better shielding, which would have a minimum impact on production costs. The rub is that DJI doesn't provide an alert if GPS should drop out. The app should definitely announce a large visual/aural warning so you can take appropriate action, and inform its users of this possibility and remedy (ATTI/manual mode). Since they ship in "Phantom Mode", this isn't an RTF product for "everybody", as their advertising suggests. But rest assured, a little reading and patience will make your DJI experience much safer, and eliminate most of the flyaway concerns, with the exception of prop/motor/esc/control board/electrical connection failure.

    Read this: viewtopic.php?f=27&t=17055
     
  18. yawnalot29

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  19. Dozer

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    Why am I not getting this issue? My P2V+ has flown over 40 flights without incident. I'm now too scared to fly it.

    Sent from my GT-I9305T using Tapatalk
     
  20. Dirty Bird

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    I have 53 flights and haven't experienced this issue either. On being too scared to fly, that's a rather expensive display piece! Use due diligence and common sense, and enjoy your bird.