Hi. Total noobie here with a SH Phantom 2 I just bought.

I'm only interested in using this to fly set paths using waypoints. But the thing is - I'm on an island in Thailand and 80% of the time I can only pick up 5 satellites. (Yes - got copper foil and tape on order!) But today I saw something that made me wonder about what I've read . . . that if the GPS link dops, the drone just hovers wherever it happens to be.

Today I got 8 satellites and went outside for a trial flight. I set the compass and plotted a short waypoint route. I changed my mind and moved to a better starting point nearby. But then I noticed that the satellites icon on my phone app was greyed out and showing only 5 satellites. BUT, looking at the waypoint route I'd already set, the original starting point where I set 'home' was still showing up, about 50 yards away (marked on the screen with a little H), and my current position (the little red plane) was also showing where I was now standing, 50 yards away from the H.

I've read replies in other forums to the same topic I'm raising here And they all say that when the GPS satellite connection is lost, the drone just stops and hovers where it happens to be until the battery dies.

My question is this - once the compass has been set and the home position successfully set, surely this will still be detectable with those 5 satellites available? But just like Google Maps, maybe only accurate to about 10 yards? If my home point has been set, then does it need all those 7+ satellites to find its way back to it? With only 5 satellites (icon on phone app greyed out) it was still showing the home point on the waypoint route on the groundatation.

Where I live on Koh Samui is littered with tall trees and there are very few big clear areas. Certainly all the things I want to video mean that my Phantom will be either out of sight or over the ocean.

I need some experienced advice here please! Can anyone say for sure what will happen in this 5 satellite situation as described?

Thanks

Not sure what you mean by "SH Phantom 2."  

When you talk about waypoints, are you referring to the Litchi app?

You need 6 satellites for GPS, but you really want 7 so that if you drop one, you won't lose GPS.  

There's something called GPS Elevation Mask which implies a problem if you are in a valley or around a lot of trees.  There will likely be satellites on the horizon which are invisible to you on the ground or at low altitudes but you will pick up once your AC reaches a certain altitude.  

When your AC loses satellites so it's down to less than 6, it loses GPS, so if you don't have control, it will hover.  And if there is a wind or even a breeze, it will flow with that wind/breeze.  But if you have control, you can still fly it home safely.  You can either fly it home because you have LOS or you can FPV it home.  If you have a live tracker, you can fly it home with that provided you are within control range.  Best to have GPS available at all times, of course.  

if the gps weakens the location accuracy decreases. when gps drops the drone is unable to tell where it is or to RTH. good as lost. i own a P4, but i guess my answes stays for P2 as well.

At least until you get used to your aircraft and the area your flying, Keep your AC in VLOS learn to fly Atti mode. Those rules apply to everyone

I assume SH = Second Hand.

When you lose satellite connection, Attitude mode kicks in.


RedHotPoker

If you are in a WayPoint Mission and you lose GPS, then the Waypoint mission stops since it relies on GPS to fly the mission which is stored in memory.  It's ok if you lose the RC connection, since the waypoint mission is not relying upon RC control.  But lack of GPS means WayPoint Mission ends.

Cancel the Waypoint mission and try to fly back in ATTI mode hoping that the GPS will recover once you go back to the place it was just working.  Also try going higher or away from any large objects.  
Always fly against the wind, so when in ATTI mode, the wind will move it closer to you. I have flown a lot of waypoint missions and I have lost RC control many times, but never GPS.  It is not normal to lose GPS, especially if you are flying over the ocean.  Do you have anything glued, like some type of a label on the top of the phantom? That can reduce the antenna's sensitivity.

I have piloted many vessels  with a GPS plotter system. These are very accurate. When these systems first came out they only used a few satellites  and were very accurate.
I'm not sure why DJI wants you to wait for so many of them to show up .
I can tell you that even today under heavy weather you can loose GPS.  Interference from space can step in these signals.
If I were you,  I would fly along the coast line where the trees can't block your signal.  Fly on clear days and start from there.
I live in wooded part of earth and trees are a beech.  

MD_Icarus Posted at 2017-2-7 14:51
If you are in a WayPoint Mission and you lose GPS, then the Waypoint mission stops since it relies on GPS to fly the mission which is stored in memory.  It's ok if you lose the RC connection, since the waypoint mission is not relying upon RC control.  But lack of GPS means WayPoint Mission ends.

Cancel the Waypoint mission and try to fly back in ATTI mode hoping that the GPS will recover once you go back to the place it was just working.  Also try going higher or away from any large objects.  

Thanks for that reply - seems spot on! (See my post below . . . )

Odan Posted at 2017-2-7 20:13
I have piloted many vessels  with a GPS plotter system. These are very accurate. When these systems first came out they only used a few satellites  and were very accurate.
I'm not sure why DJI wants you to wait for so many of them to show up .
I can tell you that even today under heavy weather you can loose GPS.  Interference from space can step in these signals.

Hi - yes - you're right. But being inexperienced means I don't know what to do or expect . . .

It's lucky that my drone is SH (second hand) as the previous owner must have done some degree of set-up already . . . longer reply below.

RobOnSamui Posted at 2017-2-8 00:32
Hi - yes - you're right. But being inexperienced means I don't know what to do or expect . . .

It's lucky that my drone is SH (second hand) as the previous owner must have done some degree of set-up already . . . longer reply below.

The number of Sats required for confident GPS Home Position setting is 6 for the P2 series and 8 or higher for newer craft that lock on both GPS and GLOSNASS systems.

From a purely technical perspective, 4 sats is the absolute minimum you need to get location but more gives greater accuracy.

GPS receivers pick up a very very faint signal so flying in a canyon or under tall trees will certainly cause a drop in reception.

RTH can be set to 'hover' or 'return home'. The latter is the default. If you are in a canyon or between trees when RTH kicks in, its bye bye bird...

Well I couldn't wait, could I!

And I have answered my own question the hard way.

The Phantom 2 uses a link app on which you can plot a pre-set route/height - DJI Vision. (To answer Mark the Droner.)  I'm using this to begin with to fly about 100 yards away from my house, make a triangle and return.  Very simple stuff, I know, but this is Thailand and in most respects it's pretty backward. I wanted to see if it would hold the wifi connection and keep the GPS lock. Also I'm surrounded by trees here, with small clearings here and there - not the ideal place to start learning.

Well- it didn't. It didn't return. I lost the waypoint satellite GPS connection.

Everything was fine until the drone got to the home leg. I could see it coming back above the trees  80 feet up and about 50 yards away. Then I suddenly lost the GPS and the drone just hung there static. So I tried to bring it back manually as it was drifting towards the trees. Being a total beginner I couldn't work out which way it was facing so whacked the altitude up. And every time I lost sight of it I did this again - end of story was that the wind up there today at 300 feet was enough to blow it out of sight.

Total  panic - I haven't had this feeling for maybe 50 years . . .

Went back in the house furious. I turned off the controller and the wifi module. Then my phone started bleeping about low battery and I turned that off too to change over to a new battery. By this time I guess about 15 - 20 minutes had passed. And everything was now switched off - controller, wifi module, phone.

Then I heard the sound of the drone - and there it was up there, 30 feet above the trees and above the home position that I had set to start with. I grabbed the controller and shoved the switches on and ran out to see the drone now about 10 feet above the ground - but maybe 20 feet away from the home point. And I managed to get it down without smashing it into the ground. (The only thing I did right.)

SO . . . this can only mean that the drone's built-in GPS system is independent from either the controller or the phone app. And when the battery level becomes critical, it returns to home. And it also means that this probably only needs 3 or so satellites to do this. (NOT the 7 satellites that DJI insist on to maintain a connection with the phone app.) And this further means that once the home point is properly set (when there are enough satellites for the app to be happy) and it's thus visible on the GPS map, then the drone will come back all by itself when the batteries get low, as long as it's high enough not to hit any obstacles.

Bl**dy great big PHEW!

Sounds like you were very lucky to recover your craft. You need to do some manual flying and get some experience in atti mode to handle GPS loss. There is a trick to fly your phantom back home that you need to learn and you should try it in a small clear area to start. When looking at your craft in flight, push the right stick forward so that it starts moving forward. Then if you see that it is moving to the right, tweak the rudder (left stick) to the right, and if it goes to the left, give some rudder to the left. What you will discover is that this will guide the phantom directly back to you. You can do this even when it so far away that you cannot tell which way it is aimed. This trick does not require video from the craft.
Have fun & good flying!

I'm still not clear on what you're flying - is it a straight Phantom 2, or is it a Phantom 2 Vision?  I'll assume it's a P2V.

Your closing paragraph has some errors.

Your P2V will fail safe at low battery.  It will auto-land at critical battery.  There is a big difference between these two ideas and it's important you understand the difference.

Your AC needs 6 satellites for GPS.  It needs 6 satellites for RTH.  It will not RTH with 5 satellites or less.  

The mobile device / app has nothing to do with anything.  What is important is the connection between your controller and the P2V.    The P2V is what needs the 6 satellites to mark the homepoint, not the app.  You can leave the mobile device at home and fly all day and everything will work fine.  The flashing lights will communicate with you and tell you everything you need to know.   

Hope this helps.

Not really Mark the Droner - you forgot to mention what the "big difference" was!

I'm still not clear on what you're flying.

Fail -Safe

Auto-Land

These are two different things.  

You really need to read your manual for whatever aircraft it is you own.  

Hope this helps.

Based upon your post above, it seems like the GPS signal came back and since you turned off the controller, a RTH was initiated and the AC returned to the Home Point at the RTH altitude.  Then the battery went down to the critical level, and a landing was initiated.  You stopped the auto landing as it was going down to land, and you landed it manually.

So everything worked as it was supposed to.

I am still not sure what caused the loss of GPS?  Try flying around there and keep an eye on the GPS signal.

I heard you need 8 satellites for the Phantom 3 Standard. Is it best to wait until 8. Also, what is the make satellites for Phantom 3 Standard or Phantom 2.

As part of the pre-take off check you should see the green "Safe to Fly GPS" before taking off.  At a bare minimum, stay at a three/four foot hover until this message is displayed.

johnsr Posted at 2017-2-8 02:14
Sounds like you were very lucky to recover your craft. You need to do some manual flying and get some experience in atti mode to handle GPS loss. There is a trick to fly your phantom back home that you need to learn and you should try it in a small clear area to start. When looking at your craft in flight, push the right stick forward so that it starts moving forward. Then if you see that it is moving to the right, tweak the rudder (left stick) to the right, and if it goes to the left, give some rudder to the left. What you will discover is that this will guide the phantom directly back to you. You can do this even when it so far away that you cannot tell which way it is aimed. This trick does not require video from the craft.
Have fun & good flying!

Yes - agreed - I really need to spend time learning how to control it manually!

KevDrones Posted at 2017-2-8 17:06
I heard you need 8 satellites for the Phantom 3 Standard. Is it best to wait until 8. Also, what is the make satellites for Phantom 3 Standard or Phantom 2.

I flown with 7 and was not aware you would need more than 3.

MD_Icarus Posted at 2017-2-8 17:01
Based upon your post above, it seems like the GPS signal came back and since you turned off the controller, a RTH was initiated and the AC returned to the Home Point at the RTH altitude.  Then the battery went down to the critical level, and a landing was initiated.  You stopped the auto landing as it was going down to land, and you landed it manually.

So everything worked as it was supposed to.

Yes - thinking about it, this makes sense. (but I'm still wondering if it really needs the 7 that DJI say  to function . . .  ) I better say it again - I am on an island off the coast of Thailand. It's a 3rd world country and there's not much point in having a flock of satellites over it (except if they are in sight of Bangkok). Usually I don't even have enough satellites for Google Maps on my phone to give me better than an approx. location of within 20 metres.

BUT - yesterday I took the top off and re-routed the GPS connector under the adhesive shielding. Almost immediately I was picking up a steady 6, and toggling between 6 and 8. So I'm hoping with fuller shielding (the copper stuff) I might get a more stable result.

blackcrusader Posted at 2017-2-9 01:47
I flown with 7 and was not aware you would need more than 3.

We still aren't sure what the OP is flying, but based on his posts, we can narrow it down to either a Phantom 2 or a Phantom 2 Vision.  

Both those aircrafts use GPS satellites.  Neither of them use GLONASS.

The minimum required satellites for GPS to work on the P2 series Phantoms is six.  It's always been that way.  And I'm 99% sure the P3S is the same since the P3S also doesn't use GLONASS.  But it's smart to fly with 7 satellites so that if you lose one you won't lose GPS.  

Mark The Droner Posted at 2017-2-9 04:13
We still aren't sure what the OP is flying, but based on his posts, we can narrow it down to either a Phantom 2 or a Phantom 2 Vision.  

Both those aircrafts use GPS satellites.  Neither of them use GLONASS.

I meant to say - it's a Vision +

Mark The Droner Posted at 2017-2-9 04:13
We still aren't sure what the OP is flying, but based on his posts, we can narrow it down to either a Phantom 2 or a Phantom 2 Vision.  

Both those aircrafts use GPS satellites.  Neither of them use GLONASS.

Sorry -I meant to say - it's a Vision +

Sorry - I meant to say - it's a Vision Plus.

Sorry for multiple posts - sudden inet freeze - moderator please delete

Just out of interest - and this very much relates to what's at the heart of my post - I've not yet seen one YouTube video  that's mentioned making sure you have satellite lock when you calibrate your compass - did I phrase that right? I mean make sure there are enough satellites up there for the GPS module to be happy.

I'm sure (from a lot of the comments above) that it's something that's totally taken for granted in first world countries. In the last week I must have watched 100 DJI Phantom beginner's tutorials. And I didn't see one that explained how setting your compass works, (and that you need to have enough satellites in view so that the satellites symbol in the Vision app lights up). Or, for that matter, that when this is successful then the little H shows up on the map when you swipe the screen, showing the home point has been established.

I think this is something that people take for granted (ie that there will be lots of satellites up there just waiting to help you fly) so they don't think to explain the process. I must have seen maybe 10 tutorials that just said something like "to set your homepoint just toggle S2 five times and that's all you need to do.".  

Looking back on it I think I was actually really lucky. I assumed that I'd have wifi contact all the time . . . which I didn't and it was quickly lost when the drone went too far.  I assumed that my home point had been set but wasn't aware of how to do it properly or how to check that it was OK. (I even made a note at the time to Google what the little H on the map meant - that's how much of a beginner I am, but also not one video I'd seen pointed this out and explained the significance).

Plus I suppose a great many "tutorials" are put together by people who are amateurs and don't explain themselves very well or don't have maybe a great command of language - the very first one I watched (he was very proud of his "plain English tutorials") said that that S2 controlled yaw, and then explained this as "turning left or right". Which simply doesn't happen. The drone doesn't "turn" at all. It rotates on its axis clockwise or counterclockwise. Very confusing for someone who had never seen a drone till a few days before to be told this.

Just a few very basic thoughts for those of you who all know what they're doing!

And thanks so much for your help and advice - it's been invaluable.  :-)

Satellite lock has nothing to do with compass calibration.  

Compass calibration needs earth's magnetic field, that is, magnetic north, to complete successfully.  Has nothing to do with satellites.  


S switch function varies for the different phantoms which is just one reason why it's important to describe your aircraft fully before posting a question or problem.

But yes, on the P2 series Phantoms, the S2 switch can reset the home point by toggling it up and down 5x or more.  The word is reset, because it will set automatically the first time you have GPS which will be moments after having acquired your sixth satellite.  

So before flight, you should watch the AC or your app and wait for the home point to set.  Flicking the S2 switch won't help.  When it gets the 6th satellite, home point will set.  You'll see an H on your screen or you'll see the AC flash green rapidly 20x AFTER the 6th satellite.  If for some reason you cannot get the 6th satellite, you might consider launching (you'll be in ATTI) and carefully gaining altitude going straight up so to minimize the GPS Elevation Mask so that you get your 6th satellite and then your home point will set itself.  You'll want to be directly over your desired home point when this happens - not over your neighbor's house, not over the ocean, etc.

Mark The Droner Posted at 2017-2-9 12:07
Satellite lock has nothing to do with compass calibration.  

Compass calibration needs earth's magnetic field, that is, magnetic north, to complete successfully.  Has nothing to do with satellites.  

Thanks for the info - appreciated.