Searching for GPS even when I have 10+ sats

[techspy]

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

 

[DDUB806]

My guess is that solo has some connection lags sometimes and causes a late flight ready. I have had times where it's in the air 30 secs after power on as for some take up to a min. I also feel that solo arms quicker when further away from transmitter, step back about 10 yrds and see what how that goes.

 

[techspy]

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.

 

[Bilge]

Do not move when it is initializing its sensors prior to takeoff....it is only doing what is designed to do.....if you pick it up or move it or lean over it after it has acquire GPS lock....then yes....it will most likely drop a few sats & indicate "Searching for GPS"

 

[Dave K]

I noticed the same thing when I installed the mRo unit... my guess was that while it takes advantage of the 2 other satellite networks, it still needs a certain number of satellites from the US network to be happy (or maybe it needs a minimum number of satellites from one of the networks). Admittedly I have no basis for that assessment... just a guess. It was pretty consistent with where it dropped out when it was just the single network.

I've never had it happen in the air so I'm not sure if guidance is actually lost when it says it's searching but still has 12 or 14 satellites.

 

[techspy]

That makes sense. I just find it a bit ridiculous that it will complain about satellite being lost when it has so many sats. I would prefer that when that warning is announced that it is an actual issue. Kinda like the boy that cried wolf. Maybe I will see what MRO has to say about it.

 

[Pedals2Paddles]

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.

 

[techspy]

I am familiar with HDOP and GPS usage in general (previous UAV Pilot for the military and current UAV support specialist.) The issue is simple. With 12 satellites locked and an HDOP of 1 or less is not a condition that should set off a "Searching for GPS" warning simply because the satellite count went down by one or two. In all other systems I use this type of warning is used for when the PDOP is more than a preset limit.

Simply put, a GPS warning should be reserved for when you are in danger of losing GPS assisted navigation, which is definitely not the case when going from 18 sats to 12 and a HDOP from .6 to 1.

 

[Pedals2Paddles]

You need to stop focusing on the Sat count and HDOP. Those numbers are not relevant to the issue you're experiencing. Please read what I said about evaluating the stability of the position fix.

 

[techspy]

I understand what you are saying. If it is indeed being caused by a a changing fix, or because the fix isn't "stable", it should not warn that it is "Searching for GPS". This warning indicates that the system is trying to find GPS satellites. Like with a cold boot where the tables are being updated. In all other systems I have experience with, a warning of this sort indicates you have lost GPS communications and have no positional awareness, which is not the case with this situation.

Anyway, thanks for your input but I am still looking for a way to change the parameters of this warning so it does not come on when there is no loss of GPS assist.

 

[Pedals2Paddles]

There is no rewording the warning. If the GPS fix is no good, regardless of the reason why, that is the message you get. And there IS a loss of GPS assist. The GPS fix is being rejected and will not be used when you see that. You're reading way too much into this, probably because you're used to much more detailed systems. With consumer UAS, you either have a usable GPS fix, or you don't. The warnings do not get into the detail of why. If you're getting that warning, you do not have a usable GPS fix, and it will not allow the GPS to be used for anything.

 

[Bilge]

Maybe....the warning should state......"Stop leaning over me or don't move me until GPS is acquired"

 

[RichWest]

Night and day difference between commercial/military and consumer drones. I'd imagine it's a conflict "failsafe" when there is a quick loss of sat count or rapid increase in HDOP, seen as an error.

May not be a legit answer, hopefully Pedals will correct me if I'm off base, as not all features of Arducopter were brought to Solo. Also there is a mention of DCM (direction cosine matrix) which may be another verification when data is in conflict.

GPS Failsafe and Glitch Protection — Copter documentation

 

[dmyhill]

I am familiar with HDOP and GPS usage in general (previous UAV Pilot for the military and current UAV support specialist.) The issue is simple. With 12 satellites locked and an HDOP of 1 or less is not a condition that should set off a "Searching for GPS" warning simply because the satellite count went down by one or two. In all other systems I use this type of warning is used for when the PDOP is more than a preset limit.

Simply put, a GPS warning should be reserved for when you are in danger of losing GPS assisted navigation, which is definitely not the case when going from 18 sats to 12 and a HDOP from .6 to 1.

I think that the system is claiming to see or track 10 sats, but not claiming to be using all 10 sats for the fix. (My limited understanding is that "fixed" is a threshold parameter that has to do with the firmware of the receiver.) So, a receiver could be tracking 10 sats, but only using 4 in the position solution. (I believe 4 is the theoretical threshold, but that would provide no checks, so there would be no way to establish a "fix" status. Thus the need for 6, or more.) If you want to get even more complex, think on this, most receivers track dozens (high end hundreds) of channels. This is because each SV transmission results in multiple paths to the receiver, and a high end receiver will track many of them, rejecting the ones that are the result of multipath.

DOP (GDOP, HDOP, VDOP) is NOT an assessment of the quality of the GPS fix. That seems to be a HUGE misunderstanding. The last time anyone had a truly bad DOP anywhere in the USA was probably 2002, unless they were in a canyon. DOP is a THEORETICAL assessment of the figure. Think a right angle triangle vs an oblique triangle...one is a strong figure, one is a week figure. That is what DOP is assessing.

A good receiver is constantly assessing and adding and eliminating sats from its solution, and using various means to determine whether the solution falls within the parameters needed for a fix.

If the receiver says, "no good", Solo has a go/no-go communication, but that decision is made by the Ublox engineers, Solo is just telling you the news. There is no warning that you are going to lose GPS assist, just a indication that it has already happened (past tense).

In the systems I use for work, there is a constant update of the HRMS and VRMS, and then there is a "fix" designation that is essentially an assessment on if the HRMS and VRMS estimates can be trusted. There is also communication about the number of visible sats, and the number being used in the current solution. If I want, I can look in a sky view, and see where each sat it is using is located. Then, I get to choose whether or not to trust the position solution. That would be unwieldy in a quadcopter, I think, and likely beyond the average consumer's desire to understand.

 

[dmyhill]

Night and day difference between commercial/military and consumer drones. I'd imagine it's a conflict "failsafe" when there is a quick loss of sat count or rapid increase in HDOP, seen as an error.

May not be a legit answer, hopefully Pedals will correct me if I'm off base, as not all features of Arducopter were brought to Solo. Also there is a mention of DCM (direction cosine matrix) which may be another verification when data is in conflict.

GPS Failsafe and Glitch Protection — Copter documentation

Military would have redundant systems for one, and likely do not have the insanely poor placement of the SOLO for the antenna.

The best and most reliable GPS in the world is most likely found in a farmer's tractor, BTW. That stuff is cutting edge. (It doesn't have access to the P and now M codes, which allow for quicker and more robust position solutions.)

 

[RichWest]

The best and most reliable GPS in the world is most likely found in a farmer's tractor, BTW. That stuff is cutting edge. (It doesn't have access to the P and now M codes, which allow for quicker and more robust position solutions.)

Cutting edge is here (ArduPilot), RTK and multiple antennas. Just depends on how much money and time you want to put in to it to have that level of accuracy. Besides tractors are typically guided in an open field with pretty much a horizon to horizon exposure.

Again, well beyond my pay scale to be in on this conversation. All consumer platforms have the same issue as in the OP, how they sort the conflict is the difference. But sure, placing Solo's antenna about 2-3" above would be an improvement as to RFI and provide the antenna a less restricted exposure. Still, would not overcome any glitch protection logic.

 

[techspy]

Well MRO felt this was enough of an issue to give me a call to discuss. The thought is that the Solo is seeing a certain degradation of either sat count, DOP and/or variance in reported position and fires off this warning. Possibly it depends on a percentage of change as opposed to worrying about the numbers it still sees etc? In any case I will see if this repros in flight or has any other strangeness. They offered to RMA it but I explained that I am pretty confident that the hardware is fine but that it is just a too sensitive of a setting with the Solo. If flights go fine I will probably just deal with it. Otherwise if the warning appears in flight and is not because GPS is actually lost, I may try adjusting the trigger point of this warning assuming I can locate it in MP or Tower.

Oh, and yes, many military UAS do have DGPS but just as many do not (like the platform I was on). Let me tell you, when you get a GPS warning in theater, it is an OH Crap moment and you hope you can fly out of the interference otherwise you are using compass/wind etc calculations as most ops were at night with little landmarks visible even with NV and thermal.

Anyway, thanks for all the input. I will update with any significant info.

 

[cryhavoc38]

I also have the mRo installed and yes, if I lean over the solo, without touching it, i tend to get the searching for gps message even though my screen shows more than enough sats for a fix. 10 plus sats.
when that happens, I power off and then fire it back up.

I'm using my backup solo because I had initially sold my primary unit, but ended up damaging it when I was getting it ready for shipment. pissed off but I'll get it sorted out eventually. The backup unit has the Rev B and when it gets the searching for GPS message even though it has enough to fly, I do the same as I did with the primary. Restart from scratch but thats just me

 

[dmyhill]

it is just a too sensitive of a setting with the Solo

Perhaps, but unlikely. That is what P2P is saying.

If this is non-typical behavior, my guess would be firmware on the UBlox chip doesn't have the optimum settings flashed for this application. That is entirely possible.

Cutting edge is here (ArduPilot), RTK and multiple antennas

Funny thing is that farmer Bob has been using that (not ArduPilot) for a decade. It is amazing how they have increased productivity and yields using that tech. As they add in drones (so now ArduPilot) for focused spraying and crop management, it will be the next revolution in yields (IMHO).

 

[dmyhill]

So, to dig deeper...The "Searching for GPS" message...
Is it the result of an EFK decision loop?
Or is it the result of no longer getting a position out of the UBlox chip?
Or could it be either one?