What if....GPS signal

RyanG · Jul 5, 2015

Ok so I am pretty petrified of flying this thing too far away. That being said I flew it today about 400 meters away from me over the ocean. I got to thinking.

What would happen if the GPS signal dropped. I think from all I have read and talked to everyone here that it would just fly in Manual mode, but would it just fall from the sky?

Would I still be able to just fly it and say take it up to 100ft in the air and get it home and be fine?

Is there a real possibility of it just falling out of the sky into the ocean and I am out $$$$? Would that be covered under 3DR's warranty if I can't get them anything back?

Thanks everyone. So far this thing is awesome.

Ryan G

Jubalr · Jul 5, 2015

Hey Ryan, You are correct. It will go in to Manual mode when it loses GPS. In manual mode it will stay close to the altitude it was when the signal was lost. From there you can fly it manually home or until GPS signal locks again. When it does, the controller will vibrate once to let you know at which poing you can hit pause or fly to go back into GPS Fly mode.

SteveMyers75 · Jul 5, 2015

The question I would have in this situation is; When does the Solo say it has dropped its GPS connection?
Is it the same as what it takes to arm it, HDOP of < 2.2 as I best recall?

In the above described situation, I would think it should go into Manual, wait about 30 seconds then go into "Dammed the HDOP, I'm RTH" mode even with HDOP of >20
As it gets closer to home, it "should" regain its position.

Even if not, it should get close enough to see it and manually land it.

In my line of thinking, this would be better than trying to figure out which way to send it via the GoPro feed.
(or worse yet, if the GoPro can't send a signal either!)

DodgeP · Jul 5, 2015

Losing GPS and losing connection to the controller are two different things. When Solo loses connection with the controller it will automatically begin to RTH. This is not true when you lose GPS. Not having GPS doesn't mean that you don't have control of Solo. You can either hit Pause or Return Home and Solo should respond; regardless of what your Satellite count or HDOP is.

SteveMyers75 · Jul 5, 2015

Yes, that's understood, GPS and Ground Station are two separate things...

This is more a "What If" scenario... in range of Ground Station, no Visual, lose GPS, GoPro battery dies.
Obviously it goes without saying that if you send out a drone with low batteries in the GoPro, you get whats coming to you.
That said, I've been a GoPro user for 6+ years and had several batteries go bad with no warning.

The question I had was, when does it decide to issue a NO GPS signal (at what HDOP value), and does it still consider trying to RTH with what little GPS it does see.

If HDOP is >20, it would still know basically what direction to start off at.
If it has absolutely no GPS then it would have absolutely no idea where "Home" was so Manual would be the only option.

RyanG · Jul 5, 2015

Thanks so much for the info.

I am new, so what is HDOP? Also if I take off with my GPS sats of say 12 or so.. Then it flys and loses GPS and I am in manual mode. Will it automatically switch back to GPS when it gets the signal back?

Thanks again everyone

Ryan G

rrmccabe · Jul 5, 2015

DodgeP said:
. Not having GPS doesn't mean that you don't have control of Solo. You can either hit Pause or Return Home and Solo should respond; regardless of what your Satellite count or HDOP is.

Solo cant return home without GPS. I don't know for sure what happens with Pause without GPS but I do know there is no way for it to be totally functional without GPS. At best I can only assume it acts like flying in manual when you let off sticks.

nacjr · Jul 5, 2015

RyanG said:
Thanks so much for the info.

I am new, so what is HDOP? Also if I take off with my GPS sats of say 12 or so.. Then it flys and loses GPS and I am in manual mode. Will it automatically switch back to GPS when it gets the signal back?

Thanks again everyone

Ryan G

HDOP

[geodesy] Acronym for horizontal dilution of precision. A measure of the geometric quality of a GPS satellite configuration in the sky. HDOP is a factor in determining the relative accuracy of a horizontal position. The smaller the HDOP number, the better the geometry.

Sarah B · Jul 5, 2015

Earlier today, I had eight satellites, and an HDOP of 5.5. The Solo--appropriately--did not give the okay to take off. I wonder if this is one of the things that was changed in the firmware upgrade, and if it's responsible for the flyaways BEFORE the upgrade. I don't remember exactly, but when my Solo went berserk, I likely only had six or seven satellites. I didn't know what HDOP was then, but I bet it was higher than it should have been.

Ian [P13] · Jul 5, 2015

The lack of HDOP checking was one of the fixes, before you could take off without a good GPS and that resulted in a few of the cases where some users ended up with crashes.

It's worth adding what is referred to as HDOP for Arducopter is really the PDOP (a long story not worth getting concerned about)...

So one of the checks is that HDOP is below 2 but also the sAcc value is checked (also in flight) as that gives a better warning than HDOP if GPS is about to become unreliable.

SteveMyers75 · Jul 5, 2015

nacjr said:
HDOP

[geodesy] Acronym for horizontal dilution of precision. A measure of the geometric quality of a GPS satellite configuration in the sky. HDOP is a factor in determining the relative accuracy of a horizontal position. The smaller the HDOP number, the better the geometry.

From what I have gathered over the years...

In very loose terms, it's often equated to horizontal positional accuracy in meters.
So HDOP of 1.8 would be approximately 1.8 Meters, or about 6 Feet
(The formula is much more complex than this, but this gives a basic ballpark accuracy and is easy to understand why larger numbers are a bad thing.)

Also, the number of Satellites does not necessarily mean better accuracy in HDOP.
If it can see 10 satellites, but they are all relatively close to each other then the HDOP will not be as good as if it can see 8 sats and they are far apart.

The photos on the right side of the Wiki do a good job at visually showing this.
https://en.wikipedia.org/wiki/Dilution_of_precision_(GPS)

There is another discussion here about upgrading the GPS Module/Antenna combo in the Solo from a NEO-7 to a NEO-M8 to see if we can improve the results.
I doubt this is something most of us want to do with a new $1K+ system...but I'm willing to give it a try.

RyanG · Jul 5, 2015

Thanks so much for the information.. Good to know.

Ryan G

Ian [P13] · Jul 6, 2015

Like I said it's PDOP that's being measured anyway, it's unlikely to be changed from people referring to it as HDOP as that was the value that was the original intent.
https://github.com/diydrones/ardupilot/issues/462

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

The uBlox NEO-M8N was tested alongside the NEO-7N by 3DR (in the US, EU and Australia) and it didn't pass their testing, the wideband antenna for one picking up more noise so the true results between the two were negligible, this has been dealt with on the Solo Facebook page a number of times. The M8N also reports satellites in the count it can't usefully utilise which artificially lowers the HDOP (and potentially PDOP) it reports so it can allow a take off when strictly it shouldn't. Finally there's also an open bug using the M8N... So in a nutshell it's a wasted modding effort right now.

https://github.com/diydrones/ardupilot/issues/2097

SteveMyers75 · Jul 6, 2015

As I said elsewhere:

It could be that some GPS algorithms discard SATs that are within a certain distance from each other, so this MAY be the reason why Solo always has a lower sat count.
This is done with units like Trimble/TopCon in agricultural systems to get better farming results.

What it doesn't explain is why the "other" Quads can operate just fine and get lower DOP numbers than what we see with out Solos. It is true that they get the advantage of GLONASS where Solo dropped the ball on that one.

I do hope that 3DR "sees the light" and jump all over GLONASS and Galileo when it's available.
The lack of GLONASS has already put them way at the back of the pack...

Then again, it could be just that the Solo has lower quality passive antenna and maybe bad plastic in the overseas made GPS cover so it doesn't see as many SAT as clearly as it should....

Ian [P13] · Jul 6, 2015

I just bet DJI tested the M8N globally and not just in their R&D HQ in China, erm not.

rrmccabe · Jul 6, 2015

What surprises me is that there is not a system in place that changes the algorithm to fly with less accuracy. In theory 4 satellites is enough to get something. If I am 3000' from home I am OK getting a warning saying "satellite view is less than ideal - proceed with caution" and having an option to RTH.

Thanks for all the good info Ian.

RyanG · Jul 6, 2015

^ That's a great idea.. Then you can have the option. I doubt I will get as far out as you but having the option to KNOW is a big deal.

Ryan G

Ian [P13] · Jul 6, 2015

The core logic of how the GPS handles things is within the uBlox itself to which 3DR, DJI or anyone else have no control over. Basically once you have less than 6 satellites the uBlox isn't providing the flight controller with anywhere near accurate positioning, so a failover to manual mode is really the best solution for now.

When the uBlox glitches it can be out by up to 500 metres, you simply can't failover to positioning that far out. You have 2 choices, land or switch to manual. Arducopter itself allows the user to choose either as a default, in the case of the solo going to manual (Altitude Hold) was the default.

rrmccabe · Jul 6, 2015

Good info again

Well hope 3DR gets it resolved quickly. The white one works well with no GPS issue !

Ian [P13] · Jul 6, 2015

The white one uses uBlox too and can't do anything about poor GPS any different, I've had a white one flyaway myself and a few Nazas try it, so I know full well GPS glitches can cause problems without additional software logic.

Arducopter has suitable additional logic and has had it for years, it's called GPS Glitch Protection and it works very well (there's examples on YouTube of the logic in testing), the issue was the code wasn't working in the original Solo firmware (no idea why not), that's now resolved. So if the uBlox gives the Pixhawk a widely erroneous location it will be ignored.