Sudden GPS loss, wide drift on RTH

[johnie]

I’m no expert but here’s my understanding of GPS.

Although you might have 20 satellites that doesn’t mean you have 20 good satellites. You need at least 4 with a good signal to get an accurate location
the bar to the right of the satellite count gives a better indication rather than the number. Lots of things affect GPS, atmospheric conditions, radio interference, line of sight to GPS satellites, having a lot of satellites in a row is not as good as having a more even spread across the sky etc etc.

The time of day also affects how many you can see and where they are. Satellites low on the horizon are not as good as those overhead, I don’t know if DJI does this but some equipment doesn’t use any satellites that are lower on the horizon than a preset value.

I use an Android app called GPS Test on my phone/tablet before I fly, I’m sure there are many others that are just as fine or better and iOS must have some available I’m sure.

GPS Test shows you how many satellites are about, where they are in the sky in relation to the horizon and their signal strength. I’ve been out ready to fly and have had next to no signal strength, my signal strength was fine after checking where the satellites where and waiting a short while until they were in a better position. Of course the reverse can also happen, you start with great signal strength but later in the day the everything has moved and your signal strength could have dropped

Most days your good to go with great GPS signal strength but I still check first

 

[Kamilo]

Similar here too. RTH and directly overhead at about 40m. Wide open field on a hilltop. GPS lost then came back.

Just checked logs, it happened at around 70 feet on top of me. Battery was 30%,

 

[vashon100]

It shouldn't create a new home point unless you instruct it to or turn it off and on (which is impossible in midair).
GPS>ATTI is compass skitzing out and the Mavic defaulting to ATTI to prevent flyaway. Symptoms is the massive arc you see. That's a giant size toilet bowl effect its trying create.

Go to an open grassy field and take your pants off and redo a compass calibration. AND REMEMBER, there is no need to do compass calibrations at every flight-sight. Only do it if stated or if you have travelled 50km+ where the magnetic declination may occur.

Those would be my logical thoughts too. It's rather confusing to me that DJI explanation is "...why it switch to ATTI mode which detects the VPS and detected other home point..." and then recommending switching to dynamic home point. The more I read these threads, it's amazing anyone can put two successful flights back to back (with all the potential GPS weirdness).

 

[Maverikster]

Why can't the Mavic simply hover at the same point where it loses GPS 'confidence' when switching to ATTI mode and forget about compass stuff and all. Just let the pilot bring it in through direct stick control. These fly aways are scary as hell. I will receive my Mavic in 2 days (as it seems), but not confident to take it out on a flight, eventhough I've got quadcopter experience. It just feels like you're out of control.

 

[Romi]

This is the second case I've seen where there has been a "satellite positioning off" message shortly after switching from "sport" mode. Wonder if it's related?

 

[Kamilo]

This is the second case I've seen where there has been a "satellite positioning off" message shortly after switching from "sport" mode. Wonder if it's related?

I would think it may, good point

 

[Romi]

This is the other case.
Lost GPS signal scare

 

[Ludvig]

Hi I just got my super Mavic after waiting for 2.5 months
I have only few flights under my belt so I am very new to this. I had already lost my GPS signals twice and it was scary as ****, lost control drifted in the wind and all that. All do I got my drone back twice by activating the go home as soon as I got my GPS back.
I thought about for some time and I was not happy and was losing my trust in the unit that I was waiting for such a long time :-(.
In my case i have figured it out Looking at on the flight log and some use of brain power... the conclusion was interference. The Mavic went from 16-18 sat to zero in a second and almost at the same spot slightly different height behind my house.
I have a satellite dish for TV system and when the Mavic got in or close to the beam the GPS went out the window and all seemed lost
So if you were flying to close to the beam or to low altitude all the same you will or can loose the GPS !!!

I am not sure if it is the same in your case or there might be similar interference sources but i think it is worth think of.

Sorry for my English as I am from Norway and it's not my first language.

 

[erkme73]

Hi I just got my super Mavic after waiting for 2.5 months
I have only few flights under my belt so I am very new to this. I had already lost my GPS signals twice and it was scary as ****, lost control drifted in the wind and all that. All do I got my drone back twice by activating the go home as soon as I got my GPS back.
I thought about for some time and I was not happy and was losing my trust in the unit that I was waiting for such a long time :-(.
In my case i have figured it out Looking at on the flight log and some use of brain power... the conclusion was interference. The Mavic went from 16-18 sat to zero in a second and almost at the same spot slightly different height behind my house.
I have a satellite dish for TV system and when the Mavic got in or close to the beam the GPS went out the window and all seemed lost
So if you were flying to close to the beam or to low altitude all the same you will or can loose the GPS !!!

I am not sure if it is the same in your case or there might be similar interference sources but i think it is worth think of.

Sorry for my English as I am from Norway and it's not my first language.

What version is your firmware? Did you update when prompted?

 

[Grimbart55]

Hi I just got my super Mavic after waiting for 2.5 months
I have only few flights under my belt so I am very new to this. I had already lost my GPS signals twice and it was scary as ****, lost control drifted in the wind and all that. All do I got my drone back twice by activating the go home as soon as I got my GPS back.
I thought about for some time and I was not happy and was losing my trust in the unit that I was waiting for such a long time :-(.
In my case i have figured it out Looking at on the flight log and some use of brain power... the conclusion was interference. The Mavic went from 16-18 sat to zero in a second and almost at the same spot slightly different height behind my house.
I have a satellite dish for TV system and when the Mavic got in or close to the beam the GPS went out the window and all seemed lost
So if you were flying to close to the beam or to low altitude all the same you will or can loose the GPS !!!

I am not sure if it is the same in your case or there might be similar interference sources but i think it is worth think of.

Sorry for my English as I am from Norway and it's not my first language.

It is hard to believe that a normal TV satellite dish causes interference. After all, the dish is only a receiver and does not send out any signal. Thus there is no "beam".

 

[erkme73]

It is hard to believe that a normal TV satellite dish causes interference. After all, the dish is only a receiver and does not send out any signal. Thus there is no "beam".

Whether a dish has the capability of affecting the MP GPS, I don't know - but a receiver absolutely can cause interference. Try putting two AM radios side by side. Put them on the same frequency, and then start moving/rotating one of them ever-so-slightly. The other receiver will start squealing even though it's not being touched.

 

[Grimbart55]

Whether a dish has the capability of affecting the MP GPS, I don't know - but a receiver absolutely can cause interference. Try putting two AM radios side by side. Put them on the same frequency, and then start moving/rotating one of them ever-so-slightly. The other receiver will start squealing even though it's not being touched.

I agree with that. But this interference, since it is not directed, should decay with 1 over the third power of the distance. If the parabolic satellite dish were used as a emitter (such as in radio communication), it would create a beam in which the intensity is only decreasing linearly with distance. But a TV dish is not an emitter, only a receiver. This if you are close to the dish, yes, you would expect some interference. But away from it it should rapidly decay away.

 

[erkme73]

I agree with that. But this interference, since it is not directed, should decay with 1 over the third power of the distance. If the parabolic satellite dish were used as a emitter (such as in radio communication), it would create a beam in which the intensity is only decreasing linearly with distance. But a TV dish is not an emitter, only a receiver. This if you are close to the dish, yes, you would expect some interference. But away from it it should rapidly decay away.

If you're trying to make my head explode with physics and math, stop it! It almost worked

 

[Grimbart55]

Sorry - was not intended