Compass Calibration

[Rubik]

After the initial calibration and library loadout of the GPS unit,...
I see no reason for this (bold). If GPS locks and hdop is good, I go.

I don't know what "hdop" is but your comment is basically the same as what I was told by Yuneec CS back in March:
"Please simply perform a compass calibration on your unit whenever you are preparing to fly in a new location over 200 miles from the previous flight. After this is completed and the unit states Ready in the GPS field you are good to go!" and:
"Simply perform the GPS [he obviously meant compass] calibrations following large moves (over 200 miles) or severe weather changes to be safe."
"Severe weather changes" is a new one to me.

 

[kd4pbs]

Horizontal Dilution of Precision.
It's the accuracy number we see for the GPS. It's the receivers educated guesstimate of how inaccurate it is in the latitude and longitude plane, expressed in meters.
And no, there is no reason to sit and wait some amount of time every so often. If the aircraft tells you it's ready to fly, and your HDOP is low, and you've got quite a few GPS satellites acquired, then it's time to fly. Almanac data lasts months (and is updated every time the GPS is on for at least 13 minutes anyway), and the ephemerides are updated constantly.

 

[Photo]

After the initial calibration and library loadout of the GPS unit,


I see no reason for this (bold). If GPS locks and hdop is good, I go.

Glider. you can never see GPS lock or hdop. Only that your H found the sats on the sky! For safe GPS lock and hdop you have to wait and stay on the ground for 14 minutes,

 

[Rubik]

Horizontal Dilution of Precision.
It's the accuracy number we see for the GPS. It's the receivers educated guesstimate of how inaccurate it is in the latitude and longitude plane, expressed in meters.

Thanks.
So, is that the same as "gps_accH" in telemetry file? Is that info available on screen somewhere while preparing to fly?

 

[PatR]

Glider. you can never see GPS lock or hdop. Only that your H found the sats on the sky! For safe GPS lock and hdop you have to wait and stay on the ground for 14 minutes,

Depends on what is being flown. Although this discussion is specific to the H, other systems display HDOP. OTOH, if you do all your flying in Angle mode GPS is not critical.

 

[kd4pbs]

Thanks.
So, is that the same as "gps_accH" in telemetry file? Is that info available on screen somewhere while preparing to fly?

Yes, that's the one.
And no, it's not available on the screen. If you've got a "ready" and several (10 or more would be a safe bet) satellites locked, barring some serious atmospheric or ionospheric conditions, you'll be fine. As has been mentioned, in angle mode, it's not that important anyway.
EDIT: I'm pretty sure that if the H does not have a GPS lock, it will not give you a green "READY".

 

[Photo]

Yes, that's the one.
And no, it's not available on the screen. If you've got a "ready" and several (10 or more would be a safe bet) satellites locked, barring some serious atmospheric or ionospheric conditions, you'll be fine. As has been mentioned, in angle mode, it's not that important anyway.
EDIT: I'm pretty sure that if the H does not have a GPS lock, it will not give you a green "READY".

I dont belive the H knows that it is GPS locked and why should it be less important in Angel mode??

 

[PatR]

The H will arm and take off without having a good GPS solution. Smart and RTH modes are most dependent on GPS and needs 10 or more sats to provide the flashing green and white ready lights. Angle mode is not as dependent on GPS and permits you to fly with a GPS solution that would not provide stable self positioning. Again, 10 or more sats are required to be provided the flashing purple and white lights indicating more advanced flight features could be enabled. The H can be flown with GPS switched off, although it's not fully "off" and still being received in the back ground if signal is present. Think of Angle mode as a "semi manual" mode with altitude and position hold capability, and flying with GPS turned off more like a "stabilized" mode where only altitude is more or less maintained but no position stability.

 

[glider]

Glider. you can never see GPS lock or hdop. Only that your H found the sats on the sky! For safe GPS lock and hdop you have to wait and stay on the ground for 14 minutes,

If HDOP (Yuneec calls it gps_accH as I recall) is unacceptable, GPS will not pass the pre-flight check. If the gps_acch is above 1.8 (?) it will fail. I verified all this over a year ago as being used to Arducopter, GPS health was extremely important considering GPS could not be disabled on the H at that time IIRC. It's in the TH telemetry files. Many crashes can be attributed to high hdop. I believe there is a time limit set before the controller will alarm out, but it's there and although it doesn't tell what exactly is wrong until the telemetry files can be evaluated, I'd place bets hdop will be the culprit more times than not.

The early LEA 6H GPS units commonly used in 3DR products were somewhat unreliable and notorious for long GPS locks (or fixes as they say). DJI wasn't known as the king of flyaways for nothing, and it had nothing to do with how long one waited for a good GPS fix. The one big factor that sunk the Solo was cheaping out on the GPS. I clearly remember the arguments at DIYDrones. Instead of moving up to M8 line, 3DR opted to go with the M7N(?) which was a huge blunder in hind sight. The reason I remember is it was my post that ignited a firestorm.

Having over 1000 autonomous missions flown on 10+ MR's, waiting 14 minutes before flying was never on the radar. 10+ good horizontal sat fix, acceptable hdop which TH indicates with 'Ready', check K-Index etc., take off. I do tend to wait an extra minute or so. Even the Solo's are up within 3-5 minutes every time. Pre M8N, I'd tend to agree more, or possibly location in the world, but I really don't know anyone else that waits 14 minutes before taking off due to GPS. If even a gut feeling the GPS is defective, it goes in the garbage.

It would seem likely the TH has a standard Ublox M8N GPS unit and could be updated for the latest satellites.