RTH During Litchi Waypoint Flight Causes Drone to Spin Around

[Billie Nelson]

Ran into a really odd Litchi waypoint mission anomaly today. My Phantom 3 Standard was on the return portion of a 6-mile round trip autonomous flight that reached out well beyond visual range since such flights are permissible out here in one of the Third World's many backwaters. About three-quarters of the way home, the drone's onboard battery power computations determined that a bee-line RTH would be necessary right away for the remaining battery charge capacity to keep the drone aloft all the way home.

Looking through the footage after the drone returned to base, I noticed that when the drone slammed on the brakes and climbed vertically about 20 feet as is the usual prelude to orienting itself towards the home point and then vectoring home, the drone instead embarked on a wild death-spin with about eight full horizontal rotations of the craft before it FINALLY wound up pointing in the right direction for the flight home. This was a really fast spin that suddenly occurred at the moment RTH kicked in, and frankly, I am surprised the drone made it home after that brief but violent departure from Litchi's normally smooth drone flight behavior.

At the time of that unexpected horizontal spin, the Phantom3S was cruising at 17mph and 150 feet AGL while hugging the terrain of a forested river valley that lay about 50-feet of altitude below the launch point, and about two miles out. Of course, the drone's signal connectivity to the RC controller shouldn't be a factor during a fully-autonomous waypoint mission programmed with Litchi. Anyway, this incident was so out of the ordinary that I decided to share its details in this forum just in case any other Phantom3S fliers out there may have encountered a similar death-spin response to their drone reaching an in-flight RTH trigger point.

In conclusion, if any other drone captains out there have seen their once-trusty drone suddenly go into a horizontal spin before locating it's intended heading at the start of an RTH, I'd be most grateful for any pointers you might be willing to share regarding how to ensure that such a potentially damaging spin doesn't recur. Crossed my mind that maybe it is time I recalibrate the GPS and the compass for good measure, but those are just wild guesses as to what might work. Thanks in advance

 

[Billie Nelson]

As the old saying goes, "When all else fails try reading the instructions", so I did a topic search that highlighted the following usual suspects when uncommanded yaws occur with Phantom series drones.

1. The IMU needs to be calibrated ( A daunting 10-minute process that requires a sprit-level checked platform)
2. The controller sticks need to be calibrated ( Presumably in the DJI Go settings page )
3. The yaw "gain" in the DJI Go settings page needs to be reset back to its default value of 125
4. The "Gimbal" icon on the DJI Go screen may have been accidentally tapped, and needs to be set back to the default value, whatever that might turn out to be.

I'll give these ideas a shot and report back in a couple of days. I only ever use Litchi and not DJI Go, so now is a good time as any to get reacquainted with the various calibration procedures.

 

[Meta4]

Crossed my mind that maybe it is time I recalibrate the GPS and the compass for good measure, but those are just wild guesses as to what might work. Thanks in advance

The incident described is an odd one.
I can't think of anything that would cause it to happen, except accidentally pushing the left stick left or right during the flight.
There's nothing you can do to "calibrate" the GPS.
Recalibrating IMU, compass etc are unlikely to make any difference.
If there were real problems with any of them, they would be causing the issue all the time, not just for a short interval.

 

[Pygar70]

It won't be no. 2. As alluded to by Meta4, uninitiated input from your sticks would persist during the entire RTH journey, not just at the start.

 

[Billie Nelson]

Something is definitely amiss with the yaw response of this Phantom3S, which may also turn out to be a causative factor in that unexplained death spin I described when the drone stopped a waypoint flight to make an RTH beeline home.

When I hand-fly the drone at low altitudes, all seems well, but when I throttle up to reach cruise altitude, the drone yaws wildly and requires drastic corrections to keep in a straight line, which is something I've never encountered with any DJI drone.

That said, when I did a google search about uncommanded yaw responses observed with DJI drones, I discovered that this problem has confounded quite a few DJI drone fliers, including a drone pilot working for the movie industry whose reputation wound up in tatters due to his Phantom 4 Version2 drone suddenly developing this same wild yaw behavior that in his case persisted after all the recommended calibrations were tried repeatedly. The man's posts in the DJI forum indicated a rising level of exasperation over the sheer persistence of the problem despite all his frantic attempts to get rid of the issue.

I'll keep trying to fix the issue with my P3S, and will certainly write back here if and when a solution materializes.

 

[Meta4]

When I hand-fly the drone at low altitudes, all seems well, but when I throttle up to reach cruise altitude, the drone yaws wildly and requires drastic corrections to keep in a straight line.

If you do a test flight to show this behaviour, using the DJI app, I could look at the .txt file the app creates to see what clues might be in there.

 

[Billie Nelson]

If you do a test flight to show this behaviour, using the DJI app, I could look at the .txt file the app creates to see what clues might be in there.

This will be very helpful Meta4. I've not accessed flight data in the past but I'll figure out how to do so with the DJI Go app today and see if I can't send over a file that captures this uncommanded yaw behavior. This drone just goes haywire when the throttle is opened wide, and I must find out why so I don't lose this drone to a crash.

 

[Meta4]

This will be very helpful Meta4. I've not accessed flight data in the past but I'll figure out how to do so with the DJI Go app today

Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report on the flight data.
Come back and post a link to the report it provides .... or just post the .txt file here.