Mavic goes into ATTI mode a lot, but HD says my GPS fix is good...

[Sleepy81]

Newbie drone flier here.
Did my 3rd flight today, and tested out a few features.

I noticed that throughout the flight I got random "ATTI mode" warnings, that lasted 10-30 sec approx. Seamed worse initially, so I assumed that it was due to the GPS almanac updating, and that it did not have a enough of sattelites to track the first few minuits of the flight.

But after the initial ATTI mode warnings went away, it seamed to improve and for the next minuits everything worked fine, and I had a solid GPS ATTI track.
Once I got down to about 25% battery left, I decided to test the return to home function. I had very conservatively set the RTH altitude to 100m, as there are a few hilltops around the local RC airport I flew at.

The drone then started to climb to 100m, but the winds aloft where fairly strong apparently, and at the same time it went into ATTI mode, and started to drift with the wind. I managed to bring it down into lower wind levels, and brought it back manually, but I almost lost sight of the MP during this maneuver.
(Sidenote: I do not want to fly BVR yet, as I am not comfortable with the drone yet, and where I live its cold outside this time of year, which means that my iPhone shuts down randomely when it gets to cold. BVR flight, ATTI mode and loss of iPhone feed = high chance of crash in my mind...)

Anyways; when I got home I checked my Healthydrones account, and found something strange. Even though it had logged ATTI mode, it also claimed I had a solid 21 sattelites locked the entire flight!?

Here is a snippet from the flight (Note this is just the end of a longer flight, I had just changed the app from DJI GO to Litchi, therfore it recorded a "new" flight on the HD website):

The MP went to ATTI mode at point F (hidden behind point E) on the map. Did not get GPS until point G, which was also about the point when I started to descendt it myself.

GPS track from healthydrones. Claims I had between 20-21 satelites throughtout the entire flight.

So I have some questiones:
1. Is it normal that the MP goes in and out of ATTI mode during normal flying?
2. Can it go into ATTI mode even if it tracks GPS?
3. Or is Helathydrones not displaying the GPS track correctly, missing the instances where it lost GPS?

 

[msinger]

Is it normal that the MP goes in and out of ATTI mode during normal flying?

No. It should only do that if the GPS data cannot be used for some reason (e.g. a compass error or interference).

Can it go into ATTI mode even if it tracks GPS?

Yes.

Or is Helathydrones not displaying the GPS track correctly, missing the instances where it lost GPS?

Try uploading your log here.

 

[MavicKhan]

"/.../ and that it did not have a enough of sattelites to track the first few minuits of the flight /.../"

I have very limited experience as a drone user but a very solid one as a pilot.

I would like to make something perfectly clear here to help the community establish a baseline, regarding GPS.

The idea that, at the moderate latitudes the bulk of this community lives in, GPS satellite constellation coverage is ever less than enough for this particular purpose should be a non-starter when analyzing the kind of events you reported.

In aviation, we now do RNAV approaches that can be solely dependent on GPS, in either mixed or stand-alone lateral/vertical configurations, with or without barometric aid, that enable precision flight down to 0.1NM.

There are checks to be performed before each approach to ensure both aircraft systems and GPS signal integrity and, in what relates solely to the GPS satellite constellation and the signals, I have yet to come across an instance where those checks were invalid.

If and when we are having problems with GPS in our UAVs, we really should focus on the machines, and and possible environmental interferences, not the signal sources.

For better understanding, please check these resources:

https://www.faa.gov/about/office_or...nss/library/factsheets/media/RNAV_QFSheet.pdf

Receiver autonomous integrity monitoring - Wikipedia

Dilution of precision (navigation) - Wikipedia

MK

 

[Sleepy81]

Greetings, fellow aviator!

I have a fairly solid understanding of GPS as a pilot myself, and I probably did not explain myself clearly when I said that "and that it did not have a enough of sattelites to track the first few minuits of the flight /".

Now, I don't know if the Mavic gets its almanac and ephemris data from the app if it has expired, but as you probably know, if it does not have the almanac, and it needs to get this from the satellites, it can take up to 12.5 min to actually get this information. Normaly, my experience shows that with modern GPS recievers you get if before, but a GPS might not track all the satellites that are physicaly in view, as it does not have the almanac for them yet. Therfore you might only have a few satellites initialy.
It the Mavic gets 4 satellites, I assume it will report "ready to fly (GPS)", as that is the lowest number of satellites needed to get a 3D fix. If I then take off with only 4 satellites "locked", and I loose one due to maneuvering or signal interfarance, I would expect the Mavic to loose GPS (no longer able to tell its posistion in 3D), ant revert to ATTI mode.
This is something I would assume would happen If the Mavic does not get almanac data from the DJI GO app. I do not know if this is true or not.

But thanks for sharing your insight anyways.

I will attempt to upload the logs to the phantomhelp.com site and see if they show the same information as the HealthyDrones.
My suspicion is that the healthydrones site does not record the loss of satellites correctly, eighter due to a bug, or to slow sample rate.

 

[MavicKhan]

I get it. Thank you for the clarification.

I think the baseline I mentioned is well established now

MK

(...PS: Is this little flying gem right down our alley or what...?)

 

[Sleepy81]

Sure is. If your a pilot and a nerd this thing is right up our ally!

Reading som more now, and I think I have figured out the problem. I flew the last flight before this one indoors, and I just remembered that I calibrated the compass prior that flight. I did not however recalibrate the compass when I moved outdoors today. Likely that is the issue.
So note to self, never calibrate the compass indoors!

If the Wx holds, I'll do another flight tomorrow to see if a compass recalibration fixes the problem.

 

[MavicKhan]

One thing I've leraned from some power

Sure is. If your a pilot and a nerd this thing is right up our ally!

Have you being talking to my kids?...They nicknamed me "Captain Gadget" a long time ago

Reading som more now, and I think I have figured out the problem. I flew the last flight before this one indoors, and I just remembered that I calibrated the compass prior that flight. I did not however recalibrate the compass when I moved outdoors today. Likely that is the issue.
So note to self, never calibrate the compass indoors!

If the Wx holds, I'll do another flight tomorrow to see if a compass recalibration fixes the problem.

After reading this forum extensively for quite a while in preparation for my Mavic arrival and, specially, after reading Msinger's awsome compass calibration guide I came to the conclusion that I won't be calibrating my compass unless under the provisions set out on that guide.

Since I immediately updated both the controller and the Mavic's FW upon receiving I pondered for while doing the calibration, since that is one of the instances Msinger recommends it to be done. Finally I decided against, flew in Beginner mode and very close quarters in the first day and since everything seems A-Ok, I will leave it at that until it is clearly needed.

MK

 

[Launchpad McQuack]

Sure is. If your a pilot and a nerd this thing is right up our ally!

Reading som more now, and I think I have figured out the problem. I flew the last flight before this one indoors, and I just remembered that I calibrated the compass prior that flight. I did not however recalibrate the compass when I moved outdoors today. Likely that is the issue.
So note to self, never calibrate the compass indoors!

If the Wx holds, I'll do another flight tomorrow to see if a compass recalibration fixes the problem.

 

[Launchpad McQuack]

Hi, When I bought my new Mav pro, I calibrated compass and did all set up in my house. Have flown 20 times in different outdoor locations without any problems or any recalibraions to compass or emu. Is this a bad idea to keep flying or should we recalibrate each location?

 

[msinger]

Is this a bad idea to keep flying or should we recalibrate each location?

You should not need to calibrate either often.

See the Compass Calibration Guide for more details on when to calibrate the compass.

 

[Launchpad McQuack]

You should not need to calibrate either often.

See the Compass Calibration Guide for more details on when to calibrate the compass.

Thank you