The common question seems to be, "Did you have GPS lock before takeoff" or something similar.

I dont profess to be an expert so I will ask the question rather than make a statement.

Is it not possible you can have 6 or more satellites on takeoff and lose GPS fix during flight?

If the answer is yes, then should it not be more important to stress that we get a GPS forcast for the number of satellites available and the likelyhood of solar interference during the flight?

I have not seen this aspect stressed or even mentioned as important in any DJI manual or even better the Quick Start Guide!

In my humble opinion I think one could argue DJI have fallen short regarding the correct procedure for safe flight.

Some of us are lucky enough to have some knowldege in this field but for someone who has not the manual has not and will not save them from an expensive mishap.

DJI need to better explain this and suggest the various web sites and Apps that are available to get this information. You can't tell me they didn't and don't use this information before testing the Phantoms etc.

Regards

Guy MacDonald

im not sure what exactly they could 'explain' about losing GPS locks in flight.  as you mentioned, knowing the solar flare activity is a good practice to review before any flight, other than that, it seems like the other main factors of GPS lock come from how/where you fly it (around things that can block or interfere with the lock).  

my experience (which is very limited) is that once i take off, my GPS locks almost always go dramatically higher than when i am on the ground.  to me, that is why it emphasizes getting a certain number BEFORE takeoff.  the last 3 flights i had 8 at takeoff and 12 or more during flight.    granted i am not flying around trees, forests, bridges, buildings, etc.  but if you were going to fly around obstructions like that, i dont think we should blame DJI for not telling us more about those implications (as to me they are straight forward).

i guess what i am asking is what exactly (some examples maybe) are you suggesting that DJI could actually do (real actionable things) to improve your knowledge of in flight GPS lock concerns?

GPS forecast?  There are always far more than 6 GPS and Glonass satellites visible at any given time.  Barriers, such as structures, terrain and even weather (clouds, precipitation) can cause the signal from a certain azimuth to be unusable.  Generally, if you have 6 or more locked before takeoff, you should have at least that while flying, unless you fly into a situation that is worse for it, such as near buildings, into a tunnel, etc.  The expected response from the P2VP is to switch to ATTI, which will simply not hold a position, laterally.  It will hold altitude, attitude and heading.  If, in ATTI or after GPS loss, it does not do these things, then there is something wrong.

For solar weather, you can check many sites, including this http://www.swpc.noaa.gov/ if you feel it makes a difference.

anthony@midmore Posted at 2015-1-2 22:08
GPS forecast?  There are always far more than 6 GPS and Glonass satellites visible at any given time ...

I don't think Phantoms are using Glonass.
And yes, while getting a home lock is important, watching in flight GPS reception is also very important. A drop in satellite coverage to 5 or less will trigger ATTI mode, but a GPS reading error may have unknown effects.

Ideally, all real errors should also trigger ATTI, but based on reports here they do not. Maybe if the Phantom is not in NAZA mode it doesn't go into ATTI?

Or, it's just a matter of the the failsafe logic needing improvement. I know they have done that at various times in the past, but there is always more that can be done.

non-Naza mode 'not going into ATTI' was my thought too.  I thought in non-Naza mode, the upper right switch was 'nothing' in middle position (i thought it was Phantom mode in position 1, phantom mode in position 2, and RTH mode in position 3) but i may have misread that.  im still flying in phantom mode (not naza mode) because i am still green so dont want to deal with anything except GPS lock and RTH as the only two options it has the ability to use.  

When you are in Phantom mode in the PT2 setup. only the s1 (right) switches are activated.  GPS, ATTI, and failsafe.  The S2 ( left switches don't do anything.  In Phantom mode, when you lose GPS, the Phantom will automatically switch to ATTI mode.  You will still maintain altitude, but you will drift with the wind and the Phantom will not maintain position.
In NAZA-M mode in the PT2 setup, the S1 switch in the UP POSITION< YOU WILL STILL HAVE GPS control, BUT if you switch to center position, that manually puts you in ATTI mode.  Then the S2 switches will be activated.  OFF, CL and HL.  You have another option of recovering your Phantom by putting S1 in ATTI and S2 in HL and pulling back the right stick, and it will come directly back to home point.

On my lost flight it appeared that when my phantom lost GPS on return home it never regained sat lock. It drifted for 8-10 minutes and never got GPS lock again. I wonder if the software does not support regaining gps lock if return home is activated when in atti mode (due to lack of GPS not from s1 switch). Never had it go more then a minute without GPS lock so for a 8 minute trip I would assume it would have regained gps.

Gerry1124 Posted at 2015-1-3 02:38
When you are in Phantom mode in the PT2 setup. only the s1 (right) switches are activated.  GPS, ATT ...

Gerry, surely in NAZA-M mode the S2 is always activated with S1 in pos1 GPS.  IT is pos1 off, pos2 CL, and pos3 HL.  It takes priority in pos2 and 3.

Gerry1124 Posted at 2015-1-3 02:38
When you are in Phantom mode in the PT2 setup. only the s1 (right) switches are activated.  GPS, ATT ...

"In NAZA-M mode in the PT2 setup, the S1 switch in the UP POSITION< YOU WILL STILL HAVE GPS control, BUT if you switch to center position, that manually puts you in ATTI mode.  Then the S2 switches will be activated.  OFF, CL and HL."

I think you are mistaken here Gerry. In NAZA-M mode, the (left) S2 switch is activated [OFF, CourseLock and HomeLock] when the (right) S1 switch is in the upper (GPS) position as well.

I'm even in the opinion that the CL and certainly HL mode NEED GPS signal to function properly. CourseLock could probably be directed just by the compass, but how would HomeLock ever be able to operate if there's no GPS signal to tell where the Home position is?

The NAZA-M quick start guide v1.26 is quite clear at page 18: http://download.dji-innovations. ... _Guide_v1.26_en.pdf

Guy, I once lost GPS signal in Phantom mode. I was flying at probably 5 meters height from an open field to in between two large 9 stories high apartment blocks.

What happens is that your LEDs turn Yellow i.s.o. Green, so that you'll know immediately that there's no GPS assistance anymore - in this situation the Phantom switches to ATTI mode automatically.

The Phantom more or less keeps it's height, however drifts on the wind, and you will have to adjust and steer the Phantom yourself in order to have it not drift into trees, buildings, structures and so on.

I had some experience with a non-GPS assisted quadcopter, and got my Phantom safely back to me; although landing isn't easy when the plane wants to skid away all the time just before you want to put it down on the ground (there was quite some wind).

So for these occasions I think it's very useful to train yourself to fly in ATTI mode from time to time - start when there's no wind ;-) Even with loss of GPS signal you will have more change to get your Phantom back safely this way.

Cheers,

Gerard

great suggestions gerard

Gerard N Posted at 2015-1-3 04:19
"In NAZA-M mode in the PT2 setup, the S1 switch in the UP POSITION< YOU WILL STILL HAVE GPS contro ...

That is just what I said. you have to have setup NAZA in your RC app on your computer for the S2 switches to be activated.  If you have your Phantom setup in GPS or Phantom mode, the S2 switches will not work, just the S1 switches will be activated.  CL and HL switch on the S2 switch will only work when your bird is setup in the RC app.

Gerry1124 Posted at 2015-1-3 05:24
That is just what I said. you have to have setup NAZA in your RC app on your computer for the S2 s ...

Sorry Gerry, I didn't read it correctly.

With "if you switch to center position, that manually puts you in ATTI mode.  Then the S2 switches will be activated" I thought that you meant that the S2 switch would only be activated when you'd switched S1 to center ATTI position.

Gerard

This might be a nice help: https://in-the-sky.org/satmap.php

Click the tab 'Map of Your Sky' and you should be able to determine how many satellites, which are above let's say 20 degs from the horizon, should be 'visible'.

G.

Ps. Don't forget to use the pull-down menu 'Select Satellites' and tick only GPS so your not mistaken bij Hubble or ISS ;-)

Gerry, I also misread in your comment: "In NAZA-M mode in the PT2 setup, the S1 switch in the up position you will still have GPS control, BUT if you switch to center position, that manually puts you in ATTI mode.  Then the S2 switches will be activated.     .It was this sentence that seemed ambiguous as it implied that S2 was only engaged when you switched to pos2  s1. and by inference was not available in s1 pos1 mode.   

guymacdonald@ip Posted at 2015-1-3 07:56
Apparently not all visible satellites are used for the triangular calculation (PDOP, TDOP) because t ...

To close to buildings will block any sats that might be on the other side of it.  That's 1 way.

guymacdonald@ip Posted at 2015-1-3 12:49
Maybe where you live but in my neck of the woods there are periods where the number of satellites f ...

It's hard to say... Theoretically 4 satellites should give a good location (3 for triangulation and another 1 for clock errors). I assume DJI goes with minimum 6 for errors detection and maybe more precision.
According to the spec, Phantoms switch to ATTI mode when the number of GPS satellites drop to 5 or less. My concern is when there are 6+ satellites and the signal is not reliable.
Because interference between the GPS unit and other electronics in the unit, there's a chance of GPS errors even when the GPS signal seems strong (see the reports about GPS drop on start recording). Some people reported that the GPS antenna is kind of weak (they reported better results after changing that ceramic element in the antenna). Also, if you take the screws out and push the top cover up while the Phantom's powered, you'll see that it gets improved GPS reception. Many users report that extra copper or even aluminum insulation improves the reception, too.
We don't know how the Phantom software for "hold position" works in that case. That's something I like to know, too.
But meanwhile, when I see that the GPS signal is not strong enough I have a few options: go higher so I get better reception (because where I fly, there are tall trees, too) or flip to ATTI mode, just in case (as that seems to avoid crazy software decisions on my behalf). I'm not sure, but I think I get longer flights in ATTI mode because there's less CPU usage and even the motors may work less (because they don't have to fight to keep the position).

ciprianboboc@gm Posted at 2015-1-3 13:29
It's hard to say... Theoretically 4 satellites should give a good location (3 for triangulation an ...

(3 for triangulation and another 1 for clock errors).

That is good if you are on the ground, but you are in a 3-d environment,  length, width, height.  You need at least 6 sats to get your position.  If you lose 1 sat, you become lost.
You are basically flying inside a box with 6 sides, with each side of the box requiring a sat signal.

Gerry1124 Posted at 2015-1-3 13:33
(3 for triangulation and another 1 for clock errors).

That is good if you are on the ground, bu ...

I disagree, Gerry. 3 satellites are enough to give you 2 points in space (intersection of 3 spheres) where one of the point is far away from Earth with quite high velocity. The 4th one is necessary because time corrections and once the correction kicks in, then you have a very good position in a 3d space from those 4 satellites.

Please see this: http://www.trimble.com/gps_tutorial/howgps-triangulating.aspx

"So by ranging from three satellites we can narrow our position to just two points in space.
To decide which one is our true location we could make a fourth measurement. But usually one of the two points is a ridiculous answer (either too far from Earth or moving at an impossible velocity) and can be rejected without a measurement."

I stand corrected, only 4 will give the required absolute minimum to determine position, but no room for error.  DJI built a small safety margin into their programming I think.

guymacdonald@ip Posted at 2015-1-4 19:14
This is what really concerns me.
Despite using 12.5 degrees minimum elevation (lower than I would us ...

Interesting, guymacdonald.  20 years of AF avionics, 14 years of GPS-assisted search and rescue and countless hobbies using GPS and I've never had a problem with GPS not gaining enough satellites, simply due to the ephemeris of the satellites.  I'll be giving this a test - run a chart, then see how many sats the P2VP finds, at that time, comparing the two.  Thank you for the interesting data.

guymacdonald@ip Posted at 2015-1-3 12:49
Maybe where you live but in my neck of the woods there are periods where the number of satellites f ...

nothing will happen if you loose GPS in naza mode, i cant speak about Phantom mode because i never used it. Im used to the Naza mode because the Phantom1 never had a phantom mode, only naza. Thats why i use this mode on my p2 as well. The phantom will just go in ATTI mode. you can check that out by yourself when flying indoors in a sports hall or something like that.

teedo757@yahoo. Posted at 2015-1-3 02:54
On my lost flight it appeared that when my phantom lost GPS on return home it never regained sat loc ...

I am amazed that failsafe mode is not failsafe, it needs constant gps locks(more than 20 seconds it goes int atti mode) and a home position. The DJI uses diversity receiver and a compass. How hard is to use the RC and WIFI(if available) signal strengths to head towards home. If they could use the doppler effect on the RC signal surely this is possible. This would enable the pilot to regain visual contact and orientation to bring it home in atti mode. Some people have suggested if you loose site of the quad, to use course lock. Point the RC in the direction you took off in and use the controls relative to that take off orientation. That is if you were pointing north at take off. You loose site of the quad south of take off position then you should push forward in course lock mode. I am not sure this will bring it home but you might get lucky and be able to see it. Seems to me we are using a global system that was designed to go work over water, large distances and great heights. When most of us fly less than a couple kilometers. Other options are Radio/TV stations(as used by light aircraft pilots), phone towers and WIFI base stations. Google has the GPS position of most of the WIFI access points from their street view application. Phone towers give amazing coverage of inhabitle regions. And Radio/TV stations already transmit data such as song titles and program subtitles. They transmit at much stronger signal strength and if they added the same info as the GPS satelites we may be able to use it.

Eraser339 Posted at 2015-3-31 06:32
I am amaze that failsafe mode is not failsafe, it needs gps locks and home position. The DJI uses  ...

If you lose sight of your Phantom, and you lost orientation of it.  All you have to do to bring it home is move s1 into (atti mode) and s2 to (home lock) pull the right stick to you, it will come back to takeoff point.  It won't matter what the orientation is.  You have to have the Phantom setup in NAZA-M mode and not Phantom mode. It will come back to the altitude it is at if you do not use the throttle to raise or lower it.

Gerry1124 Posted at 2015-3-31 06:39
If you lose sight of your Phantom, and you lost orientation of it.  All you have to do to bring it ...

Doesn't this need a GPS lock?

Eraser339 Posted at 2015-3-31 07:56
Doesn't this need a GPS lock?

Why would you lose GPS signal?  Usually you get more sats at altitude because being higher, you will not be blocked with trees, buildings etc.  If you lose control signal, it will go into RTH automatically.

Gerry1124 Posted at 2015-3-31 08:03
Why would you lose GPS signal?  Usually you get more sats at altitude because being higher, you wi ...

Bad Satellite configuration. I later found out using this thread to use GPS planner. There were only 4 or 5 American satellites in the area and a huge rain storm about 200km away. The rain storm shielded any chance of more satellites on gaining altitude.  

Eraser339 Posted at 2015-3-31 08:17
Bad Satellite configuration. I later found out using this thread to use GPS planner. There were on ...

Well if you lost sat coverage, you would be flying in what would amount to manual mode and no home point.   I've never seen less than 6 predicted, more likely 8 and above.

I use http://www.spectraprecision.fr/s ... 977.kjsp?RF=PRUFWMP with Satellite Library set to just GPS. No Glonass or Galileo. Setting the horizon to 20 degs and depending on the time of day, using the "Satellite Count" I max out at 9 and as low as 4 in a 10min interval.

Eraser339 Posted at 2015-3-31 08:35
I use http://www.spectraprecision.fr/support/gnss-planning/gnss-planning-17977.kjsp?RF=PRUFWMP with  ...

I use 10 degrees because I'm on the flat lands. Glonass and Galileo do not work with phantom.

Thanks Gerry I'm done...