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RevoMikey
lvl.2
United Kingdom
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Hi guys

When i first had the phantom, it went through the self check sequence pretty quickly, like 30 seconds and i was up in the air, i have gotten into the good habit of calibrating the compass everytime i fly but over the last few days it seems to be taking minutes rather than seconds.

Today i was down the beach and did the usual calibration, put it down and 2 minutes later she was still flickering different colours, i unplugged and replugged, again a couple of minutes later and she went all green.  i have plugged into the assistant software and no faults are apparent, the gps module clearly works as it maintains it position in even the strongest of winds.

It is cold though, does it take longer in the cold weather or am i just too damn impatient?:@

2015-1-24
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gil
Second Officer
Flight distance : 1379308 ft
United States
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I always check the kp-index before I fly.  That can affect the GPS reception:  http://www.swpc.noaa.gov/products/planetary-k-index
2015-4-27
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nig_smith
Second Officer

United Kingdom
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Hi Mikey.

If you are flying in the cold only the IMU needs to warm up to operating temperature.

If a GPS device, and this includes satnavs as well as GPS enabled multirotors, hasn't been used for a while it first needs to aquire info on satellite positions, this is usually referred to as the almanac or ephemarous, two line Kepler data that describes the satellite's orbit. Most GPS units have a small lithium cell to provide short term battery backup to the area where this almanac data is stored so that when you swap a flight battery out the Phantom will aquire a suitable lock much quicker.

Some have theorised that GPS performance can be impeded by interference from the electronics inside the Phantom or even from noise generated by a GoPro camera. I personally don't subscribe to this idea and to that end I did a video of some tests I performed on both my Phantom and my GoPro equipped F550 hex and I was unable to detect any interference in either the two GPS L-Band allocations or the Glonass allocation.

The jury is also out with regards to GPS performance during periods when the Solar K Index is high. A couple of weeks ago the K index reached a high of 8 but I didn't observe any anamolous performance in the flight of either my Phantom or my Hexacopter.

Regards

Nidge
2015-4-28
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joe
lvl.3

United States
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Nidge,
There impact of K index is not a speculation.  It is a well proven fact that you will find a great deal of documentation regarding the impacts and reasons.  This effects GPS in commercial aircraft as well as our drones.  While at a specific point and place you might be OK in general GPS performance can be dramatically affected by solar electromagnetic storms.  You may start out OK and lose a good fix in flight since the effects are variable.  This is a big part of the reason for the NOAA site and the reporting it does.  The K index is also part of what some GPS manufacturers have their GPS capable of reporting so the systems GPS unit know can report this to users real time.
As you not is specific circumstances you mileage may vary but the basics of the issue are real and significant.

As to interference from electronics this is also a real issue.  In the case of the Phantom DJI have taken the  appropriate precautions by putting a RF shield between the GPS and other electronics.  This protects the GPS from interference.  The reason for the stalk on Naza / WKM / A2 GPS systems is to distance the GPS from other electronics that can interfere.  The intensity of the interference drops by the square as with distance so a few inches dramatically reduces the interference.  I have done tests with GPS units where the HDOP can be monitored and can see significant  increase in interference when a unsheilded GPS is put close to flight electronics and RF generators.  When a RF sheild was added performance of the GPS increased dramatically
2015-4-29
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RevoMikey
lvl.2
United Kingdom
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Thanks fellas, i havent logged in for a while so only just caught up with your replys, the info you have all provided makes a lot of sense, thank you so much.

I have gotten out of the habit of calibrating every time now and i dont have any issues, it seems to have cured itself, i only do the compass dance now every month or so.  perhaps the warmer weather has made a difference as well but either way its flying great and i have full sat locks every time.

thanks again chaps.
2015-5-16
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