[Mateusz]

I had a look at your GPS unit
http://www.banggood.com/UBLOX-NEO-M8N-BN-880-Flight-Control-GPS-Module-Dual-Module-Compass-p-971082.html
and it says
Receiving Format:GPS,GLONASS,Galileo,BeiDou,QZSS and SBAS
Just out of curiosity, can you try disabling all other sats and using only GPS ? Additional check, does it happen when flying in the clear area (without any walls/buildigs in proximity of ~200 meters).

My colleague experience similar jumps on M8N that uses GPS and GLONASS, but he didn't have the problem with M6N which uses only GPS. Also I was told walls can confuse GPS by reflecting signal and creating contradicting trajectories with different timings, so you end up with jumps.

[jdl]

Yes. But I think it'd be a great improvement to address such GPS issues (detected by NoFix or PDOP > xxx) in the Revo firmware, if possible.

When in autonomous flight, I cannot guess something that can help. But when flying in Manual Auto-levelling mode, and using INS13GPS, and when such GPS glitch is detected, isn't it possible to switch for some seconds to Complementary and use simple attitude estimation based on accelerometers and gyros only?

[jdl]

I had a look at your GPS unit
http://www.banggood.com/UBLOX-NEO-M8N-BN-880-Flight-Control-GPS-Module-Dual-Module-Compass-p-971082.html
and it says
Receiving Format:GPS,GLONASS,Galileo,BeiDou,QZSS and SBAS
Just out of curiosity, can you try disabling all other sats and using only GPS ? Additional check, does it happen when flying in the clear area (without any walls/buildigs in proximity of ~200 meters).

My colleague experience similar jumps on M8N that uses GPS and GLONASS, but he didn't have the problem with M6N which uses only GPS. Also I was told walls can confuse GPS by reflecting signal and creating contradicting trajectories with different timings, so you end up with jumps.

The issue with NoFix happens regardless of the flight area. Last time is was on the open field with no buildings or trees or anything kilometers around.
I definitely suspect this is a M8N firmware problem. Not sure if M6N did the same, because I was flying then with classic CC3D and used GPS only for OSD telemetry. But I have some memories that NO GPS FIX have also occured during flights in open areas with M6N.

I'll test different settings with M8N: GPS, GPS+GLONASS, EGNOS on or off, SBAS used for ranging, integrity, corrections and combinations between them. Of course, when SBAS is used for integrity, GLONASS cannot be used.

Still, regardless if this is M8N speciffic issue or not, it would be nice to have a failsafe NoFix workaround for attitude estimation in INS13GPS and manual flight modes.

[Mateusz]

I found my old notes on M8N GPS I tested some time ago. I have 3 of those units, tested only two.

Code: [Select]

Got lock immediately after setting outside of window, 13 sats after 5-10 seconds in view and lock
- Scopes show 8-9 sats used
- No earlier training for 20min was done
- Green path on the map after enabling diagnostics shows small interval green path around window of my house, 44min no spikes
- I observed twice satellites dropped from 9 to zero on scopes, fix was lost and recovered immediately to 9 sats, but no spikes on the map

So either I haven't tested long enough for it to happen, or maybe it only happens in flight ? I haven’t flown those GPS units successfully yet for other reasons though. At least I didnt notice couple of meter jumps in a bench test.

Still, regardless if this is M8N speciffic issue or not, it would be nice to have a failsafe NoFix workaround for attitude estimation in INS13GPS and manual flight modes.

Might be a good idea to have some additional stronger filtering/smoothing before it enters EKF...

[TheOtherCliff]

I had better luck with "GPS only", but it did not fix the issue completely.

There are some things that could be done when the jump is detected, and you would not even need to leave INS13 mode.

The jumps I have seen have been associated with NoFix, and the GPS position looked normal before the jump, including having plenty of satellites, then jumped up to 200-300 meters away on the next GPS update (with 0 sats during the jump update IIRC), then quickly move back toward the original (correct) location over the course of the next 5-10 updates.  This is not an INS13 issue because "Show Diagnostics" also shows it.  In flight, even in non-GPS flight modes such as ATitude are affected, the level goes bad for the several seconds it takes to recover.

I just now created a tracking to address this issue.

[FeuerVogel666]

Hi, in the last months i was pretty busy.
Is there something new about this issue?
I really want to go flying my Copter, but i cant, because it crashes.
Do I have to buy me an other Controller or is there something going forward with Libre?
Im pretty sad about this.

[hwh]

I reread your posts earlier in this thread and downloaded the log you posted.  As f5soh said, there is a big GPS position jump just before the end.  There is an issue open ( https://librepilot.atlassian.net/browse/LP-279 ) to try to find a way around the bug in ublox's m8 gps firmware that causes this position jump but nothing has been done yet.  I've only heard of this problem with the newer M8 series gps, the older M6 and M7 gps were more reliable.  Both of the GPS I fly with are older M7 ones and I don't seem to have the problem.

Eventually someone will code something to protect against the error in the M8 gps units but my best short term suggestion would be to get a M6 or M7 gps.

[rmcferon]

I have a 450 quad with a M8 series GPS that I've flown about 40 - 50 flights of 15 min each. I haven't seen this problem.

I get a GPS lock first time of the day in less than 3 minutes.

Rest of the day it's less than 1 minute.

This is the one I have:
href"http://www.ebay.com/itm/301711214747?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX"

The only time I've seen a problem is when I first started using it.

I was using the offset of Roll=180, Yaw=180, Pitch=0 to get zeros between onboard mag and aux mag.

It flew OK but, occasionally it would loose Yaw control when flying sideways.

I changed the offset to Roll=0, Yaw=0, Pitch=180 and that stopped. 

[hwh]

The GPS problems only affect some people.  The only factor that's known to make it worse is flying near a building or house where the GPS signal bounces off the building and seems to confuse the GPS.  In wide open spaces they seem to work more reliably.  The M8 seems to be the only one that has the big jump in position, the M6 and M7 don't seem to have a problem.

[jdl]

Old thread, but I'd like to share the solution that works for me.

1. I disabled SBAS (not sure this helpd too much, but still seemed to decrease the rate "No Fix" occurences).

2. Set Dynamic Model to 4G. I suppose this is the key! In 4G - no or very little filtering performed by GPS itself. And no need this filtering to be done in the uBlox module, as the EKF that runs on the Revo board does the job better.

I've flown many hours since I changed this setting and I hadn't experienced the glitch anymore. No big jumps in position or missing GPS data. No sudden tilts or jerks. No "No GPS Fix" alarms.

[TheOtherCliff]

Do you find that PositionHold "wanders" more with it set to 4G?  I assumed that would be the case, so I have never tried it.

[karla]

Old thread, but I'd like to share the solution that works for me.

2. Set Dynamic Model to 4G. I suppose this is the key! In 4G - no or very little filtering performed by GPS itself. And no need this filtering to be done in the uBlox module, as the EKF that runs on the Revo board does the job better.

I've flown many hours since I changed this setting and I hadn't experienced the glitch anymore. No big jumps in position or missing GPS data. No sudden tilts or jerks. No "No GPS Fix" alarms.

Hi Jdl and FeuerVogel666, Thanks a lot for bringing this issue to attention. I have been struggling some 6 months with the same thing.
The only change I did from the default was to change the GPS Dynamic model from 1G to 4G, the rest is the same. The result is profound. No crazy 360 degree rolls once in any 6 minutes of stable level anymore. I have only done this with test for one day but I feel its the solution and will report back here if I have other experiences these upcoming flights.
And for TheOtherCliff, no the position hold is rock steady! (will let you know if subsequent flights show different experience).

[jdl]

Do you find that PositionHold "wanders" more with it set to 4G?  I assumed that would be the case, so I have never tried it.

Sorry for the late answer!

Yes, I think the PositionHold is more unstable now. It maybe depends on current conditions, sometimes no "wanderings", sometimes - a lot of, but I'm ok with this as it saves from large jumps in GPS position.

Yesterday I had an unexpected (and still unexplainable for me) crash. I opened a new topic for the problem, although similar to this. But I'm sure the GPS is not the cause for it. Here is the topic:

https://forum.librepilot.org/index.php?topic=2449.0