Clay
New
United States
Offline
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I have about 5 hours of flight time so far, so take my opinions with a large pinch of salt.
I was flying my spark in a big open space at sunrise a few days ago. I have a controller and phone. I flew for a few minutes around the parking lot, then headed about 200 yards away and up a hundred feet to hover over a nearby hill. I was just following the crest of the hill when the go app reported a compass error and switched to atti mode.
I centered the controls and stared at the drone expecting it to stop and hover in flight, but it continued along it's flight path. Having seen some similar videos I thought I was about to see my drone fly away forever.
A few gentle prods of the controls showed I had yaw control, but that yaw did not change flight direction. So I applied some forward thrust along with the yaw and saw a bit of positive control, though not much. More thrust and the yaw control became more positive.
It was about this time that it clicked in my head that the drone was not making any attempt to hover in position, and what I was experiencing was my "hovering" drone being blown by a strong wind over the hill.
I turned off my "drone pilot" mind and turned on my "private pilot" mind, looked at the screen, and just flew the drone. I found the beautiful sunrise on the horizon, and from there just turned back to my location and flew home manually. I had a pretty good crab in my flight which I could correct either with yaw or a bit of slip (my term for sideways thrust).
About half way back the compas error cleared and the drone again began to automatically fight the wind.
I landed, reassured myself that I didn't need to change my pants and thought about what had happened. I had no idea what up on that hill could cause a compass error. But I decided to give it another shot.
With a fresh battery I launched and again, flew some patterns around the parking lot for a few minutes with no problem. Again I headed for the hill and again, after a few minutes I got a compass error and switched to atti mode. This time I just took a bit more positive control of the drone and finished what I'd planned to do, then flew back towards the car. Again, about half way back it returned to gps mode.
My first conclusion is that I and everyone should practice flying in atti mode in the wind so you don't freak out when it happens to you. It's easy to get dependent on all the automation in the drone.
My second hypothisis is that wind was the cause of the compass error.
As the drone flies, it has access to it's longitude, lattitude, elevation, compass heading, pitch, roll, and ground track.
If the drone is pointed north, applies forward thrust, but see's it's ground track move south, the only conclusion it can draw is that the compas is wrong.
That's greatly simplified as I'm sure there are several more checks, but if the wind is gusty and the drone can't reliably predict it's direction based on thrust and compass, it will ultimately declare the compass to be wrong and ignore it. And from what I've read, once the compass is gone, it doesn't use the the GPS because what's the point if you don't know how to control the motors.
I do think that the GPS might be used to maintain altitude as the drone didn't tend to gain or loose altitude wildly and the height field continued to read out accurately.
I've flown several more times since but haven't had a repeat of the compass error.
Sorry if all this is old hat and well understood but I didn't find it discussed anywhere.
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