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Drift in GPS mode
2112 14 2015-6-30
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srtgray
lvl.2

Switzerland
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Allied with my other thread today, where I ask about the number of satellites detected, I find that I get quite a drift from my aircraft in GPS mode.  So much so that if I lightly hold the landing gear when it should be hovering, it will pull hard against my fingers.  The drift can be as much as a metre (3 feet) in any direction, which is obviously significant.  It also takes some distance to come to a halt after a manoeuver.

Is this something that can be corrected in the gain adjustment section of the assistant software?
2015-6-30
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srtgray
lvl.2

Switzerland
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Just to pre-empt the question, no I wasn't in ATTI mode.  In fact I switched between GPS and ATTI with S1 (the aircraft is in NAZA-M mode) and there was no difference in behaviour between them.  However I had the same behaviour when the craft was in Phantom control mode as well.
2015-6-30
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johnwarr
Captain
Flight distance : 6467 ft
United Kingdom
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3 Feet is well within the specifications of 2.5mtrs horizontal and 0.8mtrs vertical for GPS hovering accuracy listed In the manual.
So its normal behaviour and nothing to worry about.
2015-6-30
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Riff Raff
lvl.2

United States
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johnwarr@live.c Posted at 2015-7-1 14:22
3 Feet is well within the specifications of 2.5mtrs horizontal and 0.8mtrs vertical for GPS hovering ...

You mentioned in your other thread that you are only seeing 6 GPS satellites.  I have noticed similar drift when in a similar environment.  When I am in a better environment for GPS reception my P2V is impressively solid, drift is only a few inches.  I recall seeing 11 satellites reported at the time.

Good luck with your new bird!
2015-6-30
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srtgray
lvl.2

Switzerland
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2.5m is an enormous distance!  Certainly in videos I have seen of the Phantom 2, people aren't getting anything like that amount of drift, more like the few inches that Riff Raff reports.
2015-6-30
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roy
First Officer

United States
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Sometimes drifting is due to need IMU calibration on a level surface. The quad needs to be completely level front to back and side to side. After the IMU is calibrated re-do the compas calibration and then test to see if you drifting improved to a streaker hover.
2015-7-1
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srtgray
lvl.2

Switzerland
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OK, I'll try an IMU calibration
2015-7-1
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srtgray
lvl.2

Switzerland
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Okay, this is what I'm talking about:



As you can see, I'm trying to hold my iPhone steady so you can get an idea of the whole range of motion that the aircraft follows by itself.  It's probably inside the 2.5m horizontal spec, but I'm sure it moves more than 80cm vertically, and either way it makes it hard to get steady video footage.  You'll hear when I switch to ATTI mode and back to GPS - there's a little snap back to GPS, and it is slightly better, but not much.  I did not touch the sticks at all during this shot.

Am I just being too fussy?  Is this the range of movement that everyone gets?  There were 7 satellites locked during this video.
2015-7-1
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srtgray
lvl.2

Switzerland
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That was after a full IMU calibration, BTW.
2015-7-1
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Barney Rubbel
Captain
United States
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srtgray Posted at 2015-7-1 19:18
That was after a full IMU calibration, BTW.

Take a look at this enormous thread about IMU calibration and see if it doesn't help.  >>>  http://forum.dji.com/thread-4343-1-1.html
Sometimes the Phantom sitting on a flat surface doesn't necessarily mean the props are level. This helped me a lot. I still have a little drift when 'yawing', but nothing like it was before I leveled the props. 1m is actually pretty good as mentioned above. (Your video didn't come through. If it drifts w/o even touching ANYTHING, I'd say your GPS is not working properly)

Barney
2015-7-1
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Barney Rubbel
Captain
United States
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srtgray Posted at 2015-7-1 19:18
That was after a full IMU calibration, BTW.

OK, the video showed up now (I wasn't patient). Apparently Yaw has nothing to do with it, my bad. That does seem a little wild even for GPS. Looked like it was more stable in ATTI mode. I'd try to find a place where you get more than 6 satellites as riff raff mentioned. You might also try it on a day with a little wind. If you put it in ATTI mode and the bird follows the wind, but fights to stay still when in GPS mode, you'll at least know that it is TRYING to stay in the same place. If it still just floats with the wind, I'd recommend sending it back to have it looked at.

Barney
2015-7-1
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fwickeha
Second Officer
Flight distance : 173455 ft

United States
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srtgray Posted at 2015-7-1 19:18
That was after a full IMU calibration, BTW.

Looks like it is time to upgrade to Phantom 3.
2015-7-1
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srtgray
lvl.2

Switzerland
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Barney Rubbel Posted at 2015-7-1 21:38
OK, the video showed up now (I wasn't patient). Apparently Yaw has nothing to do with it, my bad.  ...

My inclination is that it comes back to the satellite problem.  The problem with saying "go where there are more satellites" is that (a) I've tried two places 60km apart, same issue, and (b) I'm planning on using the bird commercially, which means I don't always get to choose where I am flying.
2015-7-1
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gnixon2015
First Officer

United States
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the 2.5m drift SPEC is just that, a specification.  they are saying that it shouldnt waver more than that if at 6 sats or higher.  that doesnt mean that 2.5m isnt 'large', nor does it mean that anyone getting drift will 'get that much'.  my experimentation (and ive done plenty) seem to indicate a DIRECT CORRELATION to drift distance and sat lock count.  at 6 sats, i do drift several feet at times.  at 12 sat locks, i get inches it seems.  
2015-7-1
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Gerry1124
Captain

United States
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gnixon2015 Posted at 2015-7-2 02:13
the 2.5m drift SPEC is just that, a specification.  they are saying that it shouldnt waver more than ...

Absolutely right, the more sats you can lock on to, the more accurate your stable position will be.
2015-7-1
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