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Flying in Mountain Canyons

bheiser1

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Hi everyone - I’ve got the Mavic 2 Pro, and have been reading up on threads here and elsewhere - including a number of threads about flyaways and crashes. Needless to say I want to do whatever I can to avoid either of those. I have a question about best practice.

In my area there are some interesting places in river canyons between hills and mountains. I’m referring to National Forest lands, outside designated wilderness areas. I’ve read that the Mavic uses GPS to maintain its position, and if that signal is lost (or erroneous), it can do unexpected things. Over the years hiking in the mountains, tracking my hikes with GPS receivers (like DeLorme), I’ve seen times where the GPS signals have bounced around, placing me on the opposite side of the canyon, or other such errors. I assume the same is possible with the Mavic. There also tend to be lots of trees, so if I’m down low (e.g. following a river/creek) the signal could be lost or weak.

Is there a best practice / flying mode / technique to mitigate this, to avoid the Mavic flying away to someplace it thinks it’s supposed to be, but which is actually far away, or even crashing? Or is the best practice to just avoid these areas?

The terrain I’m talking about looks similar to this (just an example to illustrate the terrain), sometimes taller hills/mountains, sometimes narrower canyons.

AE858798-CD4E-42F2-8DE3-C394D7434CC3.jpeg
 
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Flycaster

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I would think of just staying up higher to make sure you don't lose GPS signal due to being too deep in a canyon. I've thought about this myself, I have a waterfall I really want to shoot up in Plumas County. BUT, it's in a deep and steep canyon, and if something happens, not hiking/climbing down 400 feet to retrieve the bird. So, I am still in evaluation mode to decide to try it. My first issue is watching the Sat count drop (slowly or fast??).....

Yes, this is a tough call....
 

old man mavic

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you need to make sure that where you choose to take off from,that you have enough sats locked to maintain a good GPS lock,you will also need to be aware of the obstacles in the area you intend to fly from and set your return height accordingly,if you decide to fly from the top of a canyon make sure you can keep the drone in sight and you have a clear VLOS between the controller and the drone to do this you will need to be very near to the edge so be careful of your footing as you fly
 

FoxhallGH

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There is an issue that causes a problem with GPS in this sort of terrain. Your Mavic might be seeing a lot of GPS Sat's above it, but - due to being down in a canyon - not over a very wide-spread piece of sky. GPS accuracy not only gets better with the number of sat's - but it also requires those sat's to be visible over a wide arc of sky. It's rare, but you just might get 5 or 6 sat's - but since they are all in a small e.g. 15 degrees, of sky, they don't give you enough info to get a decent positional fix in 3D.
There is also a 'dilution of Precision' effect, that can happen with GPS if receivers are receiving multiple direct and indirect 'bouncing' signals from the GPS sat's - i.e. the effect you describe where your position was obviously out!
Personally, I'd fly from the ridges where you get good GPS connection before you lift-off - and then you can be more confident that if signal is lost, the RTH feature will get your drone back to you (as long as you have spent time putting sensible RTH settings into Go4 before the flight).
 

Flycaster

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My thinking right now before I would "drop" into a canyon, is I see 1 to 2 sats. drop as I slowly descend, I'm out.....it's only going to get worse.
 

Thomas B

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@bheiser1 ... I acknowledge all the advice above, but flying in narrow canyons is something I do a lot of... just watch your bird and # of sats and you should be fine. Below pics from my bird for example. Flew from where you see me standing to get the last shot shown... shows my position was way below in the canyon.

EB6947B1-051B-4E4A-9864-0FDAE544BF06.jpegD31581E1-300D-4B90-A055-EA6A285BC6DF.jpeg
 

IShouldBeWorking

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Lots of good advice from the posts above. I’ll just add that I fly in mountain and desert canyons most of the time here in Utah. I’ve even done some flying in slot canyons. I take off in open spots that give me 12 to 13 sats before liftoff and I stay above the tree levels if there are any. The biggest caution I would give is to watch out for getting terrain between you and your Mavic. That’s the one time I’ve had trouble, was with reception from the controller, not GPS. The range on the controller is impressive but it can’t broadcast through a Mountain or canyon wall. So if you drop behind a hillside or round a bend on a canyon your bird may lose its connection.

But just keep your bird in sight and have fun. You’ll get comfortable with the terrain and wind up enjoying yourself after a while. Don’t forget to share some of the mountain footage you capture. Good luck!
 

Mossiback

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Keep in mind that if you lose GPS it will switch into Atti mode. In Atti mode it will drift with the wind and not stop when you release sticks. The best way to correct this is to gain height to reestablish GPS reception.
 

Thomas B

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Keep in mind that if you lose GPS it will switch into Atti mode. In Atti mode it will drift with the wind and not stop when you release sticks. The best way to correct this is to gain height to reestablish GPS reception.
Yes! Situational awareness of flight status is critical.
 

old man mavic

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Lots of good advice from the posts above. I’ll just add that I fly in mountain and desert canyons most of the time here in Utah. I’ve even done some flying in slot canyons. I take off in open spots that give me 12 to 13 sats before liftoff and I stay above the tree levels if there are any. The biggest caution I would give is to watch out for getting terrain between you and your Mavic. That’s the one time I’ve had trouble, was with reception from the controller, not GPS. The range on the controller is impressive but it can’t broadcast through a Mountain or canyon wall. So if you drop behind a hillside or round a bend on a canyon your bird may lose its connection.

But just keep your bird in sight and have fun. You’ll get comfortable with the terrain and wind up enjoying yourself after a while. Don’t forget to share some of the mountain footage you capture. Good luck!
loss of connection in canyons and mountains ,is one of the biggest problems when flying in such terrain, as i mentioned in post#3, it is important to make sure you have a safe return path, for the drone should it go into RTH
 

bheiser1

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Yes! Situational awareness of flight status is critical.
Keep in mind that if you lose GPS it will switch into Atti mode. In Atti mode it will drift with the wind and not stop when you release sticks. The best way to correct this is to gain height to reestablish GPS reception.

This may sound odd, but is there a way to force this mode (in safe surroundings) so I can practice, and thus be familiar with the flight characteristics when it happens unexpectedly?
 

IShouldBeWorking

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This may sound odd, but is there a way to force this mode (in safe surroundings) so I can practice
Not on any Mavic I’ve owned. The main thing is to leave yourself space to react if you have to. A toy drone with no GPS would behave like a Mavic in atti mode. Not a great option though.
 

old man mavic

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if you want to know about ATTI mode just get yourself a cheap none GPS drone and practice flying it ,you will soon realise what a difference having GPS makes dont fly it on a very windy day unless you want to see it fly off in the wind its great fun as you have to constantly keep it in one place using the sticks, if you want the ultimate thrill fly one without GPS or altitude hold that really gets the stick muscle memory working overtime
 
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Mossiback

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This may sound odd, but is there a way to force this mode (in safe surroundings) so I can practice, and thus be familiar with the flight characteristics when it happens unexpectedly?
Not sure how it works on the M2, but you can cover the rear of the MP/MPP with foil to block GPS. There is also a hack to configure a RC switch but I have not done it and do not know if it is available for the M2.

If you are adventurous you could get a set of prop guards (to reduce the pucker factor), turn off all sensors, and fly indoors away from windows.
 
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Fat Bastard

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I say go for it, with the following cautions. Only launch when you have GPS home point locked and be prepared to fly in ATTI mode. Have your RTH set for any cliffs that might be in your way. I often fly in the desert canyons near my home and accept the reality that ATTI mode might kick in when deep into the canyons. Know how to fly in ATTI mode in a moments notice. In this video I flew about 250' below takeoff and well below the tops of the ridges before rising above them.
 

DanMan32

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Note that involuntary ATTI mode due to GPS loss also means RTH will not work, including on RC signal loss.

The hack to repurpose Tripod or Sport mode for ATTI mode will still allow RTH and be able to see where you are on the map. You can also back out of ATTI mode. If you cover the GPS receiver, there's no backing out of ATTI during flight, no RTH, nor will the map show your correct position.
 
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Meta4

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Is there a best practice / flying mode / technique to mitigate this, to avoid the Mavic flying away to someplace it thinks it’s supposed to be, but which is actually far away, or even crashing? Or is the best practice to just avoid these areas?
Losing GPS signal isn't going to cause the drone to fly away to someplace it thinks it’s supposed to be, but which is actually far away.
It would lose horizontal position holding and brakes which would leave it drifting on any breeze and continuing to coast when you go hands-off on the sticks.
The number of sats available will be roughly proportional to the anount of sky visible but be aware of needing a spread of sats as described on post #56.
Lose lots of sky ... lose lots of sats
 
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Dave Maine

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The gps satellites are always moving around, and the drone constantly updates it’s choices of satellite sets to use. At any given time, some are close to the horizon. The consequence of this is that you can never be sure that flying the same location twice will have the same satellite configuration.

Also be aware that the satellites need to be distributed around in the visible sky To get a good fix. All directly overhead will not provide a good fix.
 
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