Take off with no GPS, but get gps in air?

[rctoyguy]

Kind of a multi part question, and I couldn't figure out how to summarize it in the title..

1- if you take off with no gps lock, or with, say, 5 satellites - while flying is the Phantom still attempting to lock to more?

2- if flying in gps mode, with gps lock before takeoff, then you fly into an area with no satellite coverage (warehouse, etc), do you need to switch to atti mode to keep the phantom from going nuts/getting mad that it has lost the satellites it launched with?

3- other than return to home, the only thing the satellites are helping with is left/right/front/back position hold when hovering, correct?

This is all related to a P2 in naza mode if that matters

 

[rrmccabe]

Yes it will continually update and add/remove satellites as conditions change. I have taken off from bad locations several times withe less than 6 sats knowing I will pick them up and lock as I go.

If I was going to fly into a warehouse I think I would switch to ATTI mode before I go in so there was no surprises when it was going to drop out. Just my opinion

I cant answer your last question 100% but for the most part that is true. I think there may be some overlap in technologies where the GPS assist in other areas but I am not knowledgeable enough to say for sure.

 

[HarryT]

That's correct. GPS is used to hold position, and to fly in a straight line on a windy day. It has no connection to altitude holding, which purely uses the barometer.

 

[OI Photography]

2. If your Phantom loses enough sats to go below 6, it will automatically switch to ATTI mode regardless of the switch position, and will automatically go back to GPS mode once 6 or more are locked again. Transition between modes is seamless, but the flight behavior will obviously be different when in ATTI.

3. Correct

 

[syotr]

If the warehouse has metal siding and roof, I would be concerned about confusing the compass. I believe the compass is used in ATTI mode as well.

 

[ProfessorStein]

GPS is also, of course, used for the IOC flight modes; Course Lock and Home Lock.

One thing that can lead to some trouble, though, is if you take off without descent GPS lock - ie: less than 6 satellites - your Phantom is not going to be able to establish/lock it's home location accurately. In theory, with less than 6 satellites to properly triangulate, it could very well determine it's home location errantly. So if/when the Phantom ever enters RTH (either manually, or automatically) it may try to return to a home location that's some distance away. There are a number of pilots who believe this is a chief cause for fly-aways... the Phantom is actually scurrying off to what it thinks is it's home location, because it wasn't able to lock an accurate location at take off.

This hasn't been proven, but certainly a simple method to alleviate this possibility is, if you must take off with fewer than 6 satellites in view (and your Phantom automatically defaulting to ATTI mode), take off straight up until it acquires more sats and once you see that the LEDs indicate that you have a better GPS lock (all green), then immediately reset the home location by toggling the S2 switch.

 

[rctoyguy]

Thanks for the responses everyone.. Kinda what I thought but I wanted more informed opinions. As for the warehouse, that was more of an example than a real world situation. What I have done, and I didn't even think about it at the time, was to fly through a covered parking area. Nothing strange or unusual happened, but after I did it I started wondering. I also had a situation where the place I wanted to take off from was having trouble getting more than 5 satellites. I haven't used RTH (a little scared of it to be honest) so it sounds like in that case, I would have been fine to take off with only 5.

 

[rrmccabe]

One thing that can lead to some trouble, though, is if you take off without descent GPS lock - ie: less than 6 satellites - your Phantom is not going to be able to establish/lock it's home location accurately.

If I take off I without lock I always wait for the lock in the correct position or close to it but with a higher elevation. Since I fly out of the middle of a bunch of trees usually I normally reset home with more elevation as I dont want it coming home at 66' with 75' trees

But good point

 

[RIDETOEAT]

One thing that can lead to some trouble, though, is if you take off without descent GPS lock - ie: less than 6 satellites - your Phantom is not going to be able to establish/lock it's home location accurately.

If I take off I without lock I always wait for the lock in the correct position or close to it but with a higher elevation. Since I fly out of the middle of a bunch of trees usually I normally reset home with more elevation as I dont want it coming home at 66' with 75' trees

But good point

I'm gonna have to try to remember to do this as I am always in or near fairly forested areas where I live. My town has 500' of elevation change and I live on the hillside half way between so lots of considerations and understanding to be gathered to fly from here safely. I got some interesting flights planned for ground station waypoints and will be outta sight almost beginning to end.

 

[rrmccabe]

Its common practice for a lot of people. I have been making distance runs from my house which sits in trees. Basically going out 8200' until it hits RTH. I want to make sure that I have lots of height. Normally I am at about 400' elevation so it should fly back at that but always good to lock it in at about 50' for me so I get the 50' + 66' to be safe if for some odd reason I ended up lower before it initiated RTH.

 

[stevefromsd]

I was wondering the same thing. I lost my Phantom II in the ocean today. I waited about 45 seconds for it to lock onto GPS but I didn't check to make sure it finished finding 6 satalites. I figured it would find them right after it started flying. I flew it out of sight thinking it would be fine flying back with GPS. I had done that many times including as far as 3/4 of a mile away. I know the battery was fully charged. The only thing I can think of is it never locked in to 6 satalites. I thought it would at least have found 6 satalites close enough to where it took off that I would be able to see it.

 

[Meta4]

Rather than assume and hope it has recorded home point properly, it's a lot better to be certain it has.
So easy to reset home point up in the air by flicking S2 5 times, see the confirming fast green flash and go flying knowing where it will return to. I wouldn't fly without doing it.