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what is causing my phantom to lose altitude well going forwa

Discussion in 'General Discussion' started by captain, Mar 10, 2015.

  1. captain

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    I have a phantom 2 with the GoPro and 14 channel Futaba in the last week or so ..... when I fly forward it decreases in altitude this does not happen when going in reverse. Can anyone suggest what the problem is. Thanks in advance
     
  2. lake_flyer

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    Re: what is causing my phantom to lose altitude well going f

    How did you find it decreases in altitude, do you have on screen telemetry like IOSD or did it seem to go lower the further you went out?
    If you fly your phantom away from you it seems it looses altitude rapidly.
    From side to side flying, do you still see it dropping altitude?

    Just checking, normally your P2 shouldn't drop in altitude at all in GPS mode. In Atti it could drop slightly but should not be enough to alarm you.
     
  3. lake_flyer

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    Re: what is causing my phantom to lose altitude well going f

    I would also check the mix settings in the Futaba and do a calibration in the Phantom software.
     
  4. captain

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    Re: what is causing my phantom to lose altitude well going f

    I have telemetry and fly in GPS mode it loses altitude either going forward or side to side and it was about 70 feet away. I immediately gave it up in altitude and its seem to respond slowly brought it back and it was descending on its own faster than I would like but I let it land that way
     
  5. Suwaneeguy

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    Re: what is causing my phantom to lose altitude well going f

    Just an idea. It sounds to me like if you have add ons you may want to try repositioning them.
    Something in the front of the bird is making it top heavy and thusly, causing it to lose height in that direction only.
    Get four postal scales. Put one under the corners of each landing leg. If they weigh equally, that's not the problem.
    Did it ever crash? Something may have been knocked off balance.
    But it is most likely a software issue. Fine tune the controller and bird.
     
  6. SteveMann

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    Re: what is causing my phantom to lose altitude well going f

    The GPS has nothing to do with altitude. Altitude information comes from the barometric pressure sensor inside the NAZA controller.
    When the wind is gusty the barometric pressure inside the Phantom will fluctuate and ascend or descend to keep the measured pressure the same.
    Temperature will also affect the pressure transducer. If you bring a warm Phantom outside where it's below freezing, you need to let it acclimate for a few minutes before flight.
     
  7. N017RW

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    Re: what is causing my phantom to lose altitude well going f

    There are a number of factors at play here aside from the known baro. altimeter issue(s) which must be considered.

    They include: CG, o/a weight, wind, drag, available power, and most significantly the overall system capability.

    The quad multi-rotor in as under-actuated system. It can move within 6 DoF (Degrees of Freedom) in free-space (forward/backward, up/down, left/right, pitch, yaw, and roll).

    But... it only has only 4 DoF control inputs (the motors). Add to this the system loads and you can see there will be some trade-offs in performance at some level.

    To achieve lateral flight some thrust must be vectored towards the horizontal. This reduces lift so the system must have 'headroom' or adequate dynamic range within its control inputs (the 4 motors) to compensate for the loss of lift while maintaining the desired forward speed (via pitch or roll). Additionally the accelerometers must be of sufficient quality and the sampling/filtering/etc. algorithms optimized. The Naza is one of the least expensive FCs currently out there so it may not perform as well as others out there or your expectations in all conditions.

    You may try a bit of added vertical gain to increase the sensitivity of that axis but be sure to watch for other issues as oscillations or other induced altitude 'hold' variations.
     
  8. captain

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    Re: what is causing my phantom to lose altitude well going f

    Lake_flyer i am definitely considering the baro. altimeter very informative and interesting reply thank you

    Suwaneeguy Ill try the four postal scales. It did crach but problem of decreasing attitude didnt seem to start immediately after. I am a newbe and was getting myself familiar and teaching myself the PC ground station. I programmed it to fly over 5 waypoints with sequencial numbers (signs with numbers on them) with yard sticks going out from the numbers at 12 ... 3...6...9 It did exactly what i programmed .... fly at a certain speed with the camera pointed down stop over the number (waypoint) pause and then turn to the next number. Until the last number every thing was fine then after the last number i used the controller to bring it home and when i gave it up it went down and when it hit it bounced maybe 3 times hard. I didnt remember to put the PC ground station in pause before using the controller. Surprising it only cracked the body slightly and broke the ring around the lens of the go pro which i was able to replace from an online source. I took it to a DJI dealer and they re calibrated everything. Nothing inside looked knock off or out of balance.

    I know i didnt say all of this in the begining but i thought just telling the preformance was enough. After all it does what it does no matter what happened before. All I know is iy used to fly perfectly with nothing more added than what was on during the PC ground station test by the way it was no more that 3 feet off at any of the way points in the video! Another thanks to the reply i am in debt
     
  9. Hughie

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    Re: what is causing my phantom to lose altitude well going f

    Really interesting hypothesis. The bit I dont get is why this would not affect travelling backwards. The problem is only related to forward travel.
     
  10. lake_flyer

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    Re: what is causing my phantom to lose altitude well going f

    I seems like there's something with the flight controller.
    Agreed, barometric pressure pockets might play a trick but you wouldn't see your phantom drop more than a few feet only to rise back to the original altitude after you leave the area. You probably wouldn't even notice it.

    I tend to think about the COG settings in Naza. It might be off for some obscure reason. Maybe the latest software install was corrupted.
    What I would do: re-flashing the firmware once again, or try a different version first and then upgrade to the version you want. Do the advanced calibrations and try again.
     
  11. lake_flyer

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    Re: what is causing my phantom to lose altitude well going f

    You do have FPV I recall reading? IOSDmini?
    [EDIT] you say you have telemetry. I actually hope you have FPV with IOSD.

    in that case:

    What's the pitch when flying in forward flight in GPS mode? And in backward flight? Are they (roughly) the same?

    If not, it might prove my suggestion that the centre of gravity is off. With a Phantom specifically, it should be centred (in the software). If it loses altitude in forward flight, but not in reverse, it will probably show a much larger (negative) pitch in forward flight. If the COG is not centred, the Naza will compensate with extra pitch in the (according to Naza) appropriate direction. If the pitch is too much for any given speed, the phantom will lose altitude.

    I hope that makes sense, maybe not, but I would check it anyhow and do the firmware re install. Also, hit the default button on the gains screen.

    It's good weather now with a light breeze. I might test a few things out myself today.
     
  12. landmannnn

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    Re: what is causing my phantom to lose altitude well going f

    Does it do it all the time, I do find that it behaves differently if you fly into the wind rather than with the wind.
     
  13. lake_flyer

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    Re: what is causing my phantom to lose altitude well going f

    It shouldn't make any difference. Flying with or against the wind, the airspeed will remain the same. Only the ground speed changes.
    My flight instructor always reminded me to regard air as water. Like a boat on a river. Downstream is faster than upstream but the speed log will show the same speed.

    A Phantom will not rise into the wind like an aircraft with wings. In this case the propellors are the wings. The faster a rotor spin, the lower the air pressure above that rotor, so it's sucked upwards and makes the quad fly. The Flight controller will/should compensate with power to individual motors to keep the attitude constant.
     
  14. captain

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    Re: what is causing my phantom to lose altitude well going f

    Thanks for all the replies.
    The local dealer had it, they flight tested it, said it was the main controller, they replaced it, they flight tested it, and said its flying fine.

    Test flight #1 light winds maybe at the most 5mph it went up toilet bowled little and got slightly worse so I landed.
    Test flight #2 tried taking off it tipped forward with out taking off and went on its side.
    Test flight #3 tried taking off again it tipped backwards with out taking off and went on it side.

    The dealers tech is meeting me at a field tomorrow I will keep you posted.
     
  15. jason

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    Re: what is causing my phantom to lose altitude well going f

    Mine does the same thing looses altitude flying forward and completely level in reverse.
     
  16. captain

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    Re: what is causing my phantom to lose altitude well going f

    Okay I met with the dealer today we went to a park close to his business location, the tech flew it and it performed perfectly.
    Conclusion was the main controller did fix the losing altitude problem. The location of my test flights after the main controller was replaced seemed to be the issue. When I did my test flights I was about 25 feet away from a 4 story building on one side and about 20 feet away from a three story home on the other side. Now in retrospect I do remember my satellite indication lock symbol going from 6 to 8 and blinking off and then reappearing.

    Because it flew great in one location and not in the other I think my test location was the problem. At this point without more flying I think the replacement of the main controller corrected the problem.

    Thanks to all that has participated!
     
  17. Hughie

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    Re: what is causing my phantom to lose altitude well going f

    I am missing something. Why would losing satellites temporarily, affect your height ?
     
  18. N017RW

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    Re: what is causing my phantom to lose altitude well going f

    These type of 'answers' are really not satisfying.

    Best to just say not sure unless you can repeat the experiment and get the same results again.
     
  19. judyinthesky

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    and
     
    #19 judyinthesky, Mar 30, 2015
    Last edited: Mar 30, 2015
  20. IflyinWY

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    Hello judyinthesky, cool name, welcome to the forum.

    How is your Phantom flying now, and which Phantom do you fly?