Labroides
 Core User of DJI
Flight distance : 26781877 ft
Australia
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Tillikum Posted at 7-21 14:34
https://www.phantomhelp.com/logviewer/11B31G960YUA05TXLVIO/
This is the flight log. At approx 4m8s, it changed to "P-GPS" mode, and then to "forced landing". What is P-GPS ? Looking at this, it seems like I fail to go "full up" on the left stick after this point, which presumably would have cancelled the forced landing. I probably panicked and was focused on getting it back to the side of the boat, hence the full sideways stick.
What is P-GPS ?
P-GPS iswhat DJI now calls Normal Mode.
It shows briefly because teh drone switched out of Tripod Mode to enter Autolanding.
Looking at this, it seems like I fail to go "full up" on the left stick after this point, which presumably would have cancelled the forced landing.
That's correct
In any case, I'm wondering what triggered this, since the discrepancy between VPS alt and IMU altitude occurred at 3m30s, roughly 40 seconds before forced landing was initiated ?
VPS height is the height of the drone above whatever is below it as detected by the VPS sensors.
IMU height is the height relative to the launch point measured by the barometric sensor.
It's quite normal for there to be a difference when the drone flies over something higher than the launch point.
The VPS sensors have a limited range and when they are beyond this, they show N/A.
It's not a problem to fly low over something and landing protection will protect you from accidentally crashing into whatever is below the drone.
As you get very close, it will resist descent.
If you have to hold the left stick down hard for long enough to make the drone switch to autolanding.
It's easy to check how this works when you land normally on dry land.
It's you that forces the drone to cancel the landing protection and autoland.
In the end, I'm trying to determine if using catch handle when flying from the boat is relatively safe.
In this flight, the VPS height only shows when the IMU height is <67 ft at launch and <22 ft at the end of the flight.
There are some warning messages that say: Low environmental visibility. Fly with caution.
This usually indicates an issue with fog or mist and this can also affect VPS height measurement.
On descending your VPS only starts showing very low numbers rather than N/A from 3:35.5, when you descended <22 ft.
If the VPS is seeing the stick, you'd expect that to show up right through the flight, rather than just at low altitude.
So this might be a result of mist or fog rather than VPS seeing the stick?
I suspect this was the issue.
I've subsequently tested it with and without the stick on land and found that using the stick (surprisingly) caused an error to the IMU altitude rather than the VPS altitude.
However, that was not borne out in the attached flight record where the IMU was correct and VPS was wrong. Perhaps it the sensors react differently to the stick interference when over water ?
That's odd .. It should have no effect at all on the IMU altitude which comes from measuring the air pressure.
The stick shouldn't change air pressure at the IMU sensor inside the drone, but if it's visible to the downward facing sensors, it will give false low altitude data.
Flying over water makes no difference to the way the sensors work.
Some more testing on dry land would be a good idea to confirm whether the VPS is seeing the stick and that IMU height is about right. (Small variances in IMU height are common and normal over the duration of a flight). |
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