The BIG GNSS (GPS) Issue -- The Constructive Thread

[mswlogo]

Yes ... it was fast and fine.
Any drifting complaints were due to obstacle avoidance

RTH improvement was to allow the drone to come home at the pre-set height as in the pre-M3 days
Hovering uses GPS - that's how it holds position.
It also uses VPS when down low enough.

Unless you work for DJI you are speculating as much as anyone else. You don’t know it was fine, you don’t take the calls from the field, you don’t work in QA. No, that RTH change you are referring to came in 0.500 if I understand what you are referring to. An “RTH performance improvement” was also in 0.400 release notes (when the problem started). That may have referred to other RTH features too. It’s vague enough that ONLY DJI KNOWS what it really means and covers. Again these are ALL just guesses.

This is in .500 release notes.

• Added support to set RTH altitude for Advanced RTH.

And as others commented it still is not pre-M3 behavior. But a step closer.

 

[beermat]

RTH improvement was to allow the drone to come home at the pre-set height as in the pre-M3 days

That was in the .0500 January firmware update ("Added support to set RTH altitude for Advanced RTH"). We were discussing the .0400 December update (""RTH performance improvements").

 

[mangle]

So just one question. How do you explain it working fine pre 10 December FW ?

I did not own one pre 10 december so cannot comment.

 

[51 Drones]

We have a lot of complaining in other threads about how slow the Mavic 3 is to record a home point when starting up. We have plenty of evidence that it takes longer. But we do not have enough constructive discussion. I would like to try a different approach in this thread. There clearly is something different in how the Mavic 3 acquires satellites and records the home point. If DJI isn't going to be forthright about it (not holding my breath), there are still things we can do to move the discussion forward and maybe help ourselves.

For this thread, I'd like to offer up some areas in which we can actually start to figure some things out:

1. We know one material difference between the Mavic 3 vs. prior DJI drones is the swap of GLONASS to Beidou. We do NOT know if this change impacts how long it takes to record a home point. If there are known differences in the user experience between Beidou and GLONASS, Galileo, and GPS, it would be worth knowing. Could swapping them back make a difference? It is a mere configuration change to make it happen.

2. It appears, but I cannot say for sure, that DJI has changed their "GPS Health" criteria for recording a home point. My only evidence of this is the apparent need for 12 or more sats vs. 9 or so on older DJI drones. Not only does it take longer to get SVs but it also wants more of them to get going. Can someone reference and/or document the technical details that define the relationship between SV count, HDOP, GPS Health and the time to first home point.

3. We do NOT know if DJI is using different hardware or antennas for GNSS in the Mavic 3. A tear down would tell us if there is another newer uBlox chip in there with a Taoglass antenna or if DJI is using different parts this time which may explain some of the differences in what we're seeing. I have not seen any identification of chips, antennas in tear downs so far. If you come across them, post them here. If you have a busted Mavic 3 you want to offer up for autopsy, please let me know.

4. We need to push DJI to use A-GPS. We have expensive tablets, phones and RC Pros wired up to these things. It would not be hard to download current ephemeris and almanac data via these devices. For those not familiar, A-GPS is how the GNSS is so fast on your phone. It downloads all the SV geometry, etc. from the internet instead of trying to pull it off the GNSS signal itself. This would fundamentally change the experience. The time to first home point would be under 30 seconds every time.

5. Other topics I cannot think of?

Glad I found this thread! I had 2 problems in the last 3 days, the biggest being the GPS issue. I’d like to start a record board to see who’s Mavic 3 takes the longest!

DJI Mavic 3 - GPS and Obstacle Avoidance Issues

 

[ianwood]

Any drifting complaints were due to obstacle avoidance

That's an assumption. A widely held one but we have no confirmation from DJI as to the cause. I think @beermat's theory is at least plausible.

In my view that is problematic as Galileo and BeiDou step on each others frequencies especially in the public E1-E2 bands.

How much do you know about this issue and is the concurrent use of Galileo and Beidou generally uncommon/avoided as result?

I am still curious about the hardware. If it's uBlox, it should in theory work similarly to other DJI uBlox drones (all of them, I think). If it's something else, it may play a part in what we're seeing even if it wasn't as noticeable in the launch FW.

FWIW anecdotally, I did a short flight yesterday, about 10 minutes, good conditions and never got above 12 sats! I took off with only 6 because I got tired of waiting but 12 after 10 minutes in the air is really unusual.

 

[Meta4]

I took off with only 6 because I got tired of waiting but 12 after 10 minutes in the air is really unusual.

Particularly when you are accessing sats from three different systems.

 

[beermat]

I am still curious about the hardware. If it's uBlox, it should in theory work similarly to other DJI uBlox drones (all of them, I think).

Same curiosity here, especially (as I mentioned earlier) as the DJI specs for the M3 claim a much more precise horizontal hovering accuracy range than before, and they intentionally use the phrase "High-Precision Positioning System" instead of GNSS/GPS as they have previously used for this spec.

 

[JohnnyChicago]

Downloaded UAV Forecast and GPS Planner for my phone in the field. Both usually show only 15 to 18 sats available, 20 on an above average day...maybe. If the aircraft needs to lock 10 to hover and 12 to update home point that's a margin of only 3 asthmyths above the horizon on most days. I fly in dense urban setting with glass towers, 5G & high gain wi-fi nodes. I keep it in very close and mostly just overhead so I can visually keep it in control if it shifts into Atti suddenly

 

[beermat]

Downloaded UAV Forecast and GPS Planner for my phone in the field. Both usually show only 15 to 18 sats available, 20 on an above average day...maybe. If the aircraft needs to lock 10 to hover and 12 to update home point that's a margin of only 3 asthmyths above the horizon on most days. I fly in dense urban setting with glass towers, 5G & high gain wi-fi nodes. I keep it in very close and mostly just overhead so I can visually keep it in control if it shifts into Atti suddenly

I am unsure of GPS Planner, but UAV Forecast is only an estimate, not a live reading, and without knowing what the elevation threshold is on the M3 for discarding satellites, UAV Forecast may estimate more or less than the M3 can see, depending on that setting. Additionally, in a different conversation regarding this app, it became apparent that my Android version of UAV Forecast has a setting to show BeiDou satellites and two iPhone 13 users did not have that option, so in their case, UAV Forecast could be even further significantly under-reporting the estimate of visible satellites that the M3 can actually see. Right now in Old Town Chicago, UAV Forecast with a 15 degree elevation mask estimates 20 Visible Sats with BeiDou excluded, and 30 with BeiDou included

 

[redserv]

I am sure DJI is active on this forum. It would be great customer service to chime in here and atleast let us know your view or if a fix is on its way

 

[ZoneAerial]

I am sure DJI is active on this forum. It would be great customer service to chime in here and atleast let us know your view or if a fix is on its way

I actually don’t think DJI is active on this forum at all.

 

[ianwood]

Particularly when you are accessing sats from three different systems.

It's as if one constellation was being filtered out. As if somewhere between the launch firmware and now DJI turned up some sort of filtering on GNSS input. Just throwing out guesses.

Same curiosity here, especially (as I mentioned earlier) as the DJI specs for the M3 claim a much more precise horizontal hovering accuracy range than before, and they intentionally use the phrase "High-Precision Positioning System" instead of GNSS/GPS as they have previously used for this spec.

Keep an eye out for crashed Mavic 3. I am going to resist the temptation to open mine up for the moment.

I actually don’t think DJI is active on this forum at all.

DJI, like most major corporations, monitors several forums and social media sites but only communicates through their own channels.

 

[ZoneAerial]

It's as if one constellation was being filtered out. As if somewhere between the launch firmware and now DJI turned up some sort of filtering on GNSS input. Just throwing out guesses.



Keep an eye out for crashed Mavic 3. I am going to resist the temptation to open mine up for the moment.



DJI, like most major corporations, monitors several forums and social media sites but only communicates through their own channels.

Unfortunately given DJI’s response to this it may very well be the purposeful change their generally useless support is saying.

 

[beermat]

Keep an eye out for crashed Mavic 3. I am going to resist the temptation to open mine up for the moment.

Hahaha, for a hot and crazy minute, I did contemplate if I could open one up and tap into the GNSS chip I/O with the rest of the system, be it SPI or I2C or UART, link to a microcontroller and log some meaningful low level info in the field I ain't touching mine either, but hopefully a "friend" can "find" one for me, per a different thread

 

[ianwood]

Hahaha, for a hot and crazy minute, I did contemplate if I could open one up and tap into the GNSS chip I/O with the rest of the system, be it SPI or I2C or UART, link to a microcontroller and log some meaningful low level info in the field I ain't touching mine either, but hopefully a "friend" can "find" one for me, per a different thread

If it's a uBlox chip, it's pretty trivial. Plug the UART connection into their u-center tool and you can see everything going on under the hood of the GNSS. You can even make config changes like switching from Beidou to GLONASS for example.

Not sure if the output to the flight controller is NMEA but I am pretty sure it is an easy protocol to dissect. Plenty of stuff out there for Arduino, etc.

Back in the day, I hacked into the CAN bus on the NAZA and A2 flight controllers. That was pretty in depth and most of the heavy lifting was done by someone much smarter than me. If I had more time, I might be able to lend a hand but as it is now, a tear down is about as much as I've got bandwidth for.

 

[Meta4]

Downloaded UAV Forecast and GPS Planner for my phone in the field. Both usually show only 15 to 18 sats available, 20 on an above average day...maybe

That sounds like you might be using the default configuration for those apps.
Look a little further into the details and you'll find that those apps are not showing the number of sats you'd see for GPS + Galileo + Beidou.
With three different satellite systems, that should always be well over 20

With drones using multiple satellite constellations, there is no need to check projected satellite numbers.
No matter where you are, there will always be many more sats than you need in your sky.

 

[Meta4]

I am sure DJI is active on this forum.

They aren't

It would be great customer service to chime in here and atleast let us know your view or if a fix is on its way

It would be good if they would do that on their own forum, but they don't event do that.

 

[Meta4]

It's as if one constellation was being filtered out. As if somewhere between the launch firmware and now DJI turned up some sort of filtering on GNSS input. Just throwing out guesses.

If they just filtered out one satellite system, they would still pick up enough sats fairly quickly.
If they filtered out two of three, it would still get GPS a lot quicker.
The old Phantom 2 that only used the US GPS constellation didn't have this issue.

 

[BlairAir]

Glad I found this thread! I had 2 problems in the last 3 days, the biggest being the GPS issue. I’d like to start a record board to see who’s Mavic 3 takes the longest!

DJI Mavic 3 - GPS and Obstacle Avoidance Issues

Welcome Russ to the menagerie! I was surprised when your video went up. Apparently, or anecdotally at least some users did not get long acquisition times after Decembers update. By the ssme token some claim to still not have it. While I am not calling anyone out, it appears to be few and far between and we just dont know if they are talking about INITIAL flights, or subsequent ones. I do find it nearly impossible to understand how people in the same part of the world (widely speaking as in "Southeast US" do NOT have any issue at all. Not doubting you Russ, your a straight shooter. But even you must admit that what seems to be a small number of users have... what? Different GPS Module Chipsets? If anyone can shed light on this and/or how, by most reports the issue initially cropped up in December with V01.00.0400. Some small number only after January/V01.00.0500 and even smaller sample no issue all along. These reports are not logical, assuming same code/same hardware/same general region.

For what it's worth - I have 4 months experience with Glonass + Beidou (not Galileo/ Beidou) satellite GPS system on the failed Mini 2 competitor attempt from Fimi last year. I have since parted with the X8 Mini, and I don't miss it. But it does use Glonass/Beidou.

Not sure if this is useful data but that drone would take a while to get satellite locks. If memory serves, it may have been a bit better than our more expensive example but not much.

I am losing hope as more time passes and no fix appears. Will this be the Mavic 3's legacy? It's kryptonite? Is the hardware unable to utilize Galileo sats. Quick, tell me why I shouldn't be so negative. Hello? Is thus thing on?
*crickets*

 

[51 Drones]

Welcome Russ to the menagerie! I was surprised when your video went up. Apparently, or anecdotally at least some users did not get long acquisition times after Decembers update. By the ssme token some claim to still not have it. While I am not calling anyone out, it appears to be few and far between and we just dont know if they are talking about INITIAL flights, or subsequent ones. I do find it nearly impossible to understand how people in the same part of the world (widely speaking as in "Southeast US" do NOT have any issue at all. Not doubting you Russ, your a straight shooter. But even you must admit that what seems to be a small number of users have... what? Different GPS Module Chipsets? If anyone can shed light on this and/or how, by most reports the issue initially cropped up in December with V01.00.0400. Some small number only after January/V01.00.0500 and even smaller sample no issue all along. These reports are not logical, assuming same code/same hardware/same general region.

For what it's worth - I have 4 months experience with Glonass + Beidou (not Galileo/ Beidou) satellite GPS system on the failed Mini 2 competitor attempt from Fimi last year. I have since parted with the X8 Mini, and I don't miss it. But it does use Glonass/Beidou.

Not sure if this is useful data but that drone would take a while to get satellite locks. If memory serves, it may have been a bit better than our more expensive example but not much.

I am losing hope as more time passes and no fix appears. Will this be the Mavic 3's legacy? It's kryptonite? Is the hardware unable to utilize Galileo sats. Quick, tell me why I shouldn't be so negative. Hello? Is thus thing on?
*crickets*

The oddest thing in my case is that I never had this delay before the update - launching from the exact same spots I have flown before. The inconsistency is what bothers me. Also, if you read the comments on my video, this issue is exceptionally widespread, worldwide. I think we are just stuck with it, unfortunately.