12 sats, and still no gps lock....

PatR · Jun 27, 2015

Although important, the number of satellites the system sees is not as important as HDOP. Signal strength in combination with satellite count establishes accuracy. I've already seen crash logs from someone that had good satellite count but HDOP above 2.45. During the entire flight the system was sounding the alarm "Awaiting 3D fix". The FC never had a good GPS solution but the user elected to fly in a GPS mode anyway. You really, really want HDOP <2. The lowest I've ever seen it with any hobby grade system was 0.85, but those days are very, very rare.

At the moment we are being subjected to a lot of solar storm activity and GPS signal is being degraded accordingly. Check the various web sources for current GPS precision projections before planning to fly in a GPS controlled mode. Remember that RTL/RTH is GPS dependent to function correctly.

thefrog · Jun 27, 2015

HDOP is synthetic number only indicates best theoretical horizontal precision given the current constellation and number of satellites. Actual precision is usually much worse and depends on many factors. SOLO have uBLOX NEO-7M GPS module with added bandpass filter and pre-amplifier, but due to limitation of the NEO-7 it only uses GPS sats with WAAS. No Glonass here. Newer uBLOX GPS receivers like these from the series 8 can do simultaneous GPS and GLONASS reception what can help in some terrain or in urban scenarios.

PatR · Jun 27, 2015

Or, as established with some very high end systems, totally confuse the solution. Unless using military grade hardware that is not "de-tuned" for civilian use, only so much can be done to obtain high accuracy GPS precision. An option is to use a DGPS and RTK system but those are neither affordable or sized for our purposes.

In the long run every MR flyer should be prepared and capable to fly in a manual or stabilized mode the moment directional control in a GPS mode becomes evident.

Stdquad · Jun 27, 2015

PatR said:
Although important, the number of satellites the system sees is not as important as HDOP. Signal strength in combination with satellite count establishes accuracy. I've already seen crash logs from someone that had good satellite count but HDOP above 2.45. During the entire flight the system was sounding the alarm "Awaiting 3D fix". The FC never had a good GPS solution but the user elected to fly in a GPS mode anyway. You really, really want HDOP <2. The lowest I've ever seen it with any hobby grade system was 0.85, but those days are very, very rare.

At the moment we are being subjected to a lot of solar storm activity and GPS signal is being degraded accordingly. Check the various web sources for current GPS precision projections before planning to fly in a GPS controlled mode. Remember that RTL/RTH is GPS dependent to function correctly.

Very interesting PatR. Please tell me where you found this in the logs. Does this number show up somewhere in the app?

Please clarify

Stdquad · Jun 27, 2015

PatR said:
Or, as established with some very high end systems, totally confuse the solution. Unless using military grade hardware that is not "de-tuned" for civilian use, only so much can be done to obtain high accuracy GPS precision. An option is to use a DGPS and RTK system but those are neither affordable or sized for our purposes.

In the long run every MR flyer should be prepared and capable to fly in a manual or stabilized mode the moment directional control in a GPS mode becomes evident.

Maybe this will help. Definition of HDOP values

DOP Value Rating Description
< 1 Ideal Highest possible confidence level to be used for applications demanding the highest possible precision at all times.
1-2 Excellent At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications.
2-5 Good Represents a level that marks the minimum appropriate for making business decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user.
5-10 Moderate Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended.
10-20 Fair Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location.
>20 Poor At this level, measurements are inaccurate by as much as 300 meters with a 6 meter accurate device (50 DOP × 6 meters) and should be discarded.
The DOP factors are functions of the diagonal elements of the covariance matrix of the parameters, expressed either in a global or a local geodetic frame.

PatR · Jun 27, 2015

Stdquad said:
Very interesting PatR. Please tell me where you found this in the logs. Does this number show up somewhere in the app?

Please clarify

Play telemetry back in Mission Planner.

thefrog · Jun 27, 2015

PatR said:
Or, as established with some very high end systems, totally confuse the solution. Unless using military grade hardware that is not "de-tuned" for civilian use, only so much can be done to obtain high accuracy GPS precision. An option is to use a DGPS and RTK system but those are neither affordable or sized for our purposes.

In the long run every MR flyer should be prepared and capable to fly in a manual or stabilized mode the moment directional control in a GPS mode becomes evident.

Real world GPS+GLONASS test results, not bad at all:
http://electronicdesign.com/test-amp-measurement/real-world-drive-tests-declare-verdict-gpsglonass

PatR · Jun 27, 2015

I work with military grade uas and the difference in GPS precision is astounding. Bear in mind we aren't driving cars here.

Stdquad · Jun 27, 2015

PatR said:
I work with military grade uas and the difference in GPS precision is astounding. Bear in mind we aren't driving cars here.

Thanks PatR for some great info. Have a good day.

thefrog · Jun 27, 2015

Actually the difference in precision (User Range Error - URE) between the military PPS Service based on Dual Frequency P/Y-Code and WAAS augmented civilian GPS is not so big at all. In most earth regions is the URE 1-3m RMS with the civilian and 0.5 - 1m RMS with the military.

1013D · Jun 28, 2015

Flew again today and had a similar issue to what I described in the OP.

had 10 sats with HDOP of 2.4
waited a good 3 or so minutes, it varied a little but never got better than that. so I powered down the solo (and only the solo, left the controller on and ap connected), then powered it back up and after 20 seconds or so it was ready to fly with 8 sats and HDOP of 2.8 . flew fine too. (during the flight sats went up to 13 and HDOP below 2)

so there is something weird going on. if it will not let you fly and you have plenty of sats, cycle the solo power and it will probably work.

thefrog · Jun 28, 2015

1013D said:
Flew again today and had a similar issue to what I described in the OP.

had 10 sats with HDOP of 2.4
waited a good 3 or so minutes, it varied a little but never got better than that. so I powered down the solo (and only the solo, left the controller on and ap connected), then powered it back up and after 20 seconds or so it was ready to fly with 8 sats and HDOP of 2.8 . flew fine too. (during the flight sats went up to 13 and HDOP below 2)

so there is something weird going on. if it will not let you fly and you have plenty of sats, cycle the solo power and it will probably work.

It usually takes some time to get good HDOP and sat count. I usually wait few minutes after the GPS lock so the WAAS DGPS correction is applied. RTL in open space is spot on as well as well as position hold in pause.

1013D · Jun 28, 2015

I got 2.4 HDOP pretty quickly....then just waited for 3 or so minutes for the controller to allow for takeoff....no go. so I power cycle the solo, and it is ready to go in 30 seconds with a higher HDOP number.