Searching for GPS even when I have 10+ sats

techspy · Mar 30, 2017

That is the question. If we could determine the trigger it would help in figuring this out.

Flyinglawnmower · Mar 31, 2017

Pedals2Paddles said:
You're annoyed because you're assuming there is nothing more to an acceptable GPS lock than the number of satellites. The number of satellites is actually the least relevant thing to the Solo accepting a GPS lock. There is a minimum satellite parameter. The value is 6. There is a minimum HDOP value, which is 2.4. Those are the things you can SEE on your screen. It's also looking at movement. If it the fix is moving, as in not stable, the GPS lock is rejected. There are maximum horizontal and vertical movement values that I can't name off the top of my head. If it's above that, the fix is no good and it will continue waiting for it to improve.

Guess what happens when you lean over the solo? You are putting yourself between it and sky. The fix horizontal and vertical position will immediately drift, causing the fix to be rejected by the solo. This is normal and expected.

Flyinglawnmower · Mar 31, 2017

Pedals2Paddles said:
You're annoyed because you're assuming there is nothing more to an acceptable GPS lock than the number of satellites. The number of satellites is actually the least relevant thing to the Solo accepting a GPS lock. There is a minimum satellite parameter. The value is 6. There is a minimum HDOP value, which is 2.4. Those are the things you can SEE on your screen. It's also looking at movement. If it the fix is moving, as in not stable, the GPS lock is rejected. There are maximum horizontal and vertical movement values that I can't name off the top of my head. If it's above that, the fix is no good and it will continue waiting for it to improve.

Guess what happens when you lean over the solo? You are putting yourself between it and sky. The fix horizontal and vertical position will immediately drift, causing the fix to be rejected by the solo. This is normal and expected.

As always P2P, your advice is rock solid.

Frank Foster · Mar 31, 2017

There is what seems to be strange behavior, but I ain't no way close to being an expert on the subject. I've wondered why sometimes my Solo's might go from 5 or 6 sats, while searching, to "0", then start the counting up again, 3,4,5, It seems to start over sometimes, on it's own. I know it's smarter than me, but still seems strange.

Pedals2Paddles · Mar 31, 2017

I'm not sure how many different ways I can word this, so I'll try again. There are no other warnings or messages on the Solo controller or solo app related to the GPS. It does not distinguish specific type of problem. It does not care what the reason for the lack of a usable GPS fix is. That's the warning you get regardless. If the sat count is less than 6, the HDOP is less than 2.5, or the position fix is too unstable, you get that warning. The sat count and HDOP is on the screen for you to see if you want to determine for yourself which it is. But suffice to say with the mRO GPS, it will likely never be a sat count problem, and unlikely to be an HDOP problem. This is a consumer oriented product. Simplicity was the goal. The target audience was not a detail oriented operator of a Reaper.

If you use a more convention UAS ground station like Mission Planner or Tower, it provides three different warnings. Sat count, HDOP, and "Need 3D Fix", which is the position stability message.

Frank Foster · Mar 31, 2017

P2P I understand completely what you've been saying. I just wanted to comment on how mine seems to start over, from time to time. Going from 4 to 5 sats, then all at once "0", then starts again, this all before there is a "lock".

Pedals2Paddles · Mar 31, 2017

I know, wasn't directed at you. As to that issue, I've never seen that before either.

dmyhill · Mar 31, 2017

Pedals2Paddles said:
.It does not care what the reason for the lack of a usable GPS fix is.

So would "unstable 3d Position" mean that the GPS stopped agreeing with the IMU, Compass, Barro?

And, I think it is easy to forget how easy it is to hinder GPS signals. Sure my phone is pretty much right on, most of the time, but sometimes it jumps 30 feet away (for whatever reason). In those situations, you want GPS to not be used.

The location of the built in unit might be part of the equation as well. Since maybe 80 degrees (horizontal) of the sky between 15 and 0 degrees of elevation is masked by the battery, (but not necessarily masked in the solution, the number of sats, or the DOP), simply leaning over the unit could certainly cause issues.

SPP · Mar 31, 2017

I read Ublox-8 materials, as I am curious on how it chooses between GPS & GLONASS.
The U-8 track both system at the same time, but I am sure it will only choose 1 as final output to Solo pixhawk.

Here is the curious question :
If say GPS sats already 6 or better and 2.4 HDOP or better, while GLONASS sats are not yet 6 or HDOP not 2.4 or better, will the Searching For Satellite message still pops out ?

dmyhill · Mar 31, 2017

I am not sure, but I would think the M8N would be able to combine the constellations.

SPP · Apr 1, 2017

dmyhill said:
but I would think the M8N would be able to combine the constellations.

I don't think M8 can combine constellations of GPS and GLONASS, as these two run on different almanac.
I mean the analogy is like having two surveyors at the same time :
- say GPS will tell Solo pixhawk that the position is X + 1 meter "approx" to the north. The "approx" being dilution of precision.
- while GLONASS will tell Solo pixhawk that the position is X + 1 meter approx to the south
Perhaps M8 will decide based on certain parameters, which positioning data is best to choose from, and output it to Solo.

Here is what Ublox wrote:
https://www.u-blox.com/sites/defaul...M8-7-Multi-GNSS_WhitePaper_(UBX-14002009).pdf

u-blox M8: high performance positioning u-blox M8 acquires and tracks two GNSS systems concurrently – default is GPS and GLONASS.

Concurrent reception of GPS and BeiDou or even concurrent GLONASS and BeiDou reception can be selected on-the fly. Optimized signal reception circuitry in combination with software algorithms and advanced tracking and search engines capitalize on the quality, and not only the quantity, of satellites used, providing optimal solutions in GNSS hostile environments.

Also I am wondering, since in some areas, free correction satellite ( SBAS ) is visible, in USA we get WAAS, in Europe we get EGNOS and in Asia sometime I can get Indian GAGAN and sometimes Japanese MSAS, when will M8 decide to use this correction signal ?
As far as I know, only SBAS sats can be "added" into GPS constellation, as it is designed to augment and add accuracy. I forgot where I read on Arducopter ( so it may not apply to Solo ), I think there was a mention of this SBAS/Differential thingy on how they implement it. I think it may even contribute to positioning "jump".

FAQ
What is the difference between GPS and EGNOS?
GPS is a global navigation satellite system (GNSS) that allows anyone with a GPS receiver to navigate from anywhere in the world. EGNOS is a satellite based augmentation system (SBAS) that makes the GPS signal more precise and also provides an integrity signal about GPS performance by broadcasting error corrections to the users via three geostationary satellites over Europe. This means that without a GPS signal, EGNOS does not work.

I think since now we speak of two different global sat nav system ( GNSS ) the GPS and GLONASS, it will be wise to call each one as GNSS and not an umbrella name as GPS

Few things I know :

AA. There is no such thing as centimeter accuracy from freebie GPS or GLONASS GNSS. It won't happen as the earth atmosphere seems to be the major obstacle. However accuracy is indeed getting better over the past 10 years. I have not done accuracy sampling per se now, compared to 2001 - 2004 when I was still diving FAD made of sunken buses on weekly basis. Those days and since it is 1 week a part positioning data, up to 25 meters accuracy is acceptable for me. Each week I visited this FAD at 30 meters of water, I will need to do a 25 meters radius search, as the "X" coordinate I logged first time, will seemingly "shift" some 25 meters away. Every week I will record a new coordinate, up to a time I accepted this "upto 25 meters drift" and just keep 1 coordinate and do 25 meters search pattern

BB. I think as far as a particular day GNSS accuracy, if for smart shots, I rather have a GPS which will smooth out positioning data for that day slowly over a period of time, instead of getting intermittent correctional feed which even if it is super accurate , but can suddenly make Solo move 2-3 meters to some X position within say minutes. I don't know how to explain this properly, but I think you get what I mean.

CC. I tested the Solo auto landing RTL last weekend and its not bad, its about 60cm drift max.

Too bad my home are is not open sky. Too many neighbours with building taller than mine. Otherwise I will do experimental logging each day at same spot over say a week or two and see what kind of positioning drift do I get in my area.

.

dmyhill · Apr 1, 2017

There is a bit of a misunderstanding here. For Solo's purposes, unless you are using a preprogrammed mission, the overall accuracy is irrelevant. You could be 1000 feet from the real world coordinates, and it wouldn't matter... as long as that shift maintained through the entire flight.

Also, the issue of different almanacs is no issue at all. Almanacs tell the receiver the ephemeris data, but differences are irrelevant here, since both are known frameworks and if they were different, there is a known conversion. Nothing in that link indicated to me that the M8 uses one at a time, instead, it is "concurrent". The GLONASS might have a different precision, but using both at the same time has been done for over a decade now in various receivers.

SPP · Apr 1, 2017

Yes agree, for solo smart shots and if repeated over many days , only then the overall accuracy is important.

Also, the issue of different almanacs is no issue at all. Almanacs tell the receiver the ephemeris data, but differences are irrelevant here, since both are known frameworks and if they were different, there is a known conversion. Nothing in that link indicated to me that the M8 uses one at a time, instead, it is "concurrent". The GLONASS might have a different precision, but using both at the same time has been done for over a decade now in various receivers.

Nice info, thank you DM. This is interesting, I will look this up on how they combined GPS dan GLONASS data as single output. It might come handy some day

mike sember · Apr 1, 2017

P2P is correct. You can not move solo at all before launching. SOLO has pre arm checks and it has to be on a stable surface or it will not launch. I have been dealing with this issue for the last year because it is really the only thing i don't like about solo. I bought it to take off from a boat. i soon realized that it will not take off and give me the same message because the boat is rocking. Some of the other drones can take off from a unstable surface, but not solo. I actulally just found out yesterday that solo did come out with the new "boat mode" that i have been waiting on. The new pixhawk 2.1 claims that it can now launch on a unstable surface with the latest firmware. We will see. Until then, a still get made fun of by my friends when solo gets grounded on the boat. lol.

h8id · Apr 1, 2017

Loosely related... The mRo has a multiple frequency antenna, but many of the M8N GPS you can order have a $5 cheaper antenna that is only good for GPS... No mention of that in the specs though... Was true in my case. Seems common but not commonly known.

yt lee · Apr 4, 2017

techspy said:
I am not talking about a delay for flight. It gets a lock and says that it is ready. But if go lean over it, or pick it up to move it, it drops a couple sats and gives the warning. I am trying to figure out how going from 18 sats to 10-15 causes it to say "Searching for GPS" when it obviously has not lost its lock.

When you lean over , you may obstruct the gps antenna and cause a drop in shop. The number of gps is not the determining factor. The quality of gps signal is.

Ralph E. Johnson · Apr 5, 2017

techspy said:
I just updated to the MRO glonass GPS and am getting up to 18 sats where I was getting 7. Problem is, I still get the stupid "Searching for GPS" warning, even when it has 10 or more sats. I can let it sit and get up to 18 sats. Then if I got to the Solo and lean over it, or pick it up, it will drop a few sats and start saying "Searching for GPS". Why is it complaining about GPS when it has 10-15 sats and an HDOP of less than 1.0?

Thanks

Yes I have the same card and I lose signal with 15 sats when I am only 100' away.