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No GPS during yaw.

Discussion in 'General Discussion' started by Darrell1, May 13, 2013.

  1. Darrell1

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    Flying this weekend in some pretty windy conditions, I noticed a particular characteristic and since I've only been flying about a month, I'm not sure if it is due to the new firmware or not.

    In GPS mode, my Phantom will hold its position beautifully, but when you rotate (yaw), the wind will freely blow it during that time. As soon as you let go of the control stick and stop the rotation, it will fly back to the GPS point it had before you started the rotation.

    Anyone else notice this?
     
  2. tvpopta

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    Yep, I'm having the same thing. To some extend the phantom can keep a ground course while compass heading changes (tested this in course lock mode), but apparently not while keeping a fixed position.
     
  3. TickTock

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    That may be by design. Perhaps the compass signal is noisy and requires filtering before it can be reliably used. To avoid the software sending a signal to move in the wrong direction, it probably requires the compass result to be stable before attempting any correction.
     
  4. Gizmo3000

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    I kinda noticed something similar,. at low altitude (less breeze), it would spin around on a dime
    but up higher in a slight breeze, it would definitely wander around a bit. (which may or may not provide smoother video?)
     
  5. toolman2a

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    ok guys this is how it works gps is to hold it in posistion hands off sticks ,, when you move the right stick you are taking control of the craft with limits, manual mode has no limits thats why ya can flip it and roll it in manual, same with the left stick, you can over ride the barometer by giving it more or less throttle ,, when ya let go if the sticks gps takes over to hold it where you moved it too.wind and ground effect can effect yaw, so thats why it moves and gps will drift a bit its not perfect, usually within a meter square,, same with the barometer, wind pressure can effect it also and temperture,, thats why you get some up and down drift.. nuff said :D
     
  6. Darrell1

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    My point was just to inform. GPS does NOTHING to hold a location DURING yaw. As soon as you stop the rotation, it will move back to the position it was in before you started the rotation.

    So, in high wind, it is not possible to simply rotate and hold the same position. It will start to blow away - during a slow rotation, it will blow away quite a distance. When you stop, it will fly back to where the rotation started.
     
  7. tanasit

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    A few members claimed that they can do the pirouette in circle around themselves in HL. :?
    If so the GPS must be still in control or function while the Phantom was given the yaw control.
    I will have to go to the big field and try that myself.

    We have it too easy with Phantom and taking it for granted in terms of altitude hold and GPS positioning.
    When I started off with Arduino board using MuliWiiconfig to set the parameters just to get a decent altitude hold (they call it BAR short for barometer), it took me a month with perhaps over 100 sets of parameter combinations.
    Right out of the box, the Phantom has a much better ATTI mode already!

    As for the GPS drift, it always happens to me in the beginning of the flight but a minute or so later it gets better.
    Some days even with wind gust 15-20 mph, GPS mode still holds it position as good if not better than I control it myself.
     
  8. tvpopta

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    Thats quite likely it; a magnetic compass isn't as quick and precise as a gyro; but a gyro needs to be calibrated. With IOC turned off, only the magnetic compass is used for yaw orientation sensing, and this can't be fast enough to correct for wind drift during yaw input.
    With IOC on, the yaw gyro is calibrated to either the takeoff heading or whatever you reset it to, and that in turn coupled to a (right stick) control input direction. So basically gyro overrules the magnetic compass; that way it can keep flying a straight line even though yaw changes. It would be interesting to see if the phantom does a better job at maintaining gps position in IOC mode while yawing :)
     
  9. mercillus

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    I was watching mine in the wind. What I notice is when the craft is tiling to the the left to counter wind from the right. Then I turn the craft (yaw left lets say) I watch the craft. Its still leaning initially to the direction it WAS when I started the yaw. The craft quickly realizes it was turned and starts to tilt over to a new angle to get back to its GPS coords.. I then tried a fast yaw and a sLoW one!!! The faster one kept it in place more so than the slower one did. My guess is the tilt it had didn't react fast enough when spinning quickly.

    This being the first GPS enabled craft I have ever flown what are the expectations of it? Does the S800 stay in perfect place when spinning fast or slow? Or even the F550?
     
  10. Darrell1

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    I just thought that during the rotation, the GPS would hold it in place. As it turns out, it seems the GPS does nothing until you stop the rotation. Then it checks, notices it moved, and moves it back.

    So, if it is windy and you are low between a couple trees, when you rotate, you could get blown into a tree. It's no big deal and I'm not complaining, it's just good information to know.
     
  11. Joel_t

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    Had this problem yesterday afternoon. Was flying above my house and went to do a pan of the area and as I started to pan the Phantom started drifting away. Thought GPS was having trouble but it held perfectly stable while not yawing. Glad to know it's just a design thing and not my particular Phantom.
     
  12. ElGuano

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    This is how it typically seems to act, but it is not technically true. The Phantom WILL attempt to maintain position with rudder control. It does a very poor job of it in order to maintain yaw authority, but if you yaw slowly and continuously, it will begin to drift with the wind, and then come back against the wind. I asked this of DJI a while back and it was confirmed. Not a lot of people believe it when I say this though, since the positional hold is very weak and easily defeated by a mild wind.