Drone deviate & diagonal descent without command

Hello -

I am using a Mavic Pro 2 (last firmware applied), piloting with iPhone 11

For the last couple of flights I have been having some problems with my drone.

What I have been seeing are 2 things : the drone seems to deviate from its trajectory (eg I want it to fly in a straight line whereas it seems to pull towards the left). It was a nice warm day with very light breeze.

The other problem is as it progresses, the drone slowly descends on its own.

The only warning messages I have had during the flight is “obstacle avoided”. That could potentially explain when I was making it pass through a path in the middle of the woods; however when I do a test with active track it seems to work smoothly & seamlessly.

I did some further tests to see what was happening. I went out in an open field and the drone was flying more or less straight but it was still descending. There is no obstacles and no weak signals. Moreover the altitude is giving me really strange readings. Sometimes it would say I am in the minuses (eg -1.5 meter) but it was not possible!

In my last flight, I was in a wide empty building (like a hangar). And there I have had some very odd behaviour and readings. According to the drone, I had reached the maximum altitude (I was only at 3 meters and there was room to go up), there was an obstacle that was avoided (there were no obstacle). The altitude readings were completely off and nonsensical. (I will include the log below)

At one point I saw that the drone was deviating towards to the left so I corrected it by commanding it to go right but it did not respond. It went completely nuts, took up speed and made a sharp veer to the left and boom, hit a plastic window and fell.

According to flight log it was saying it was avoiding an obstacle but there was none!

Here are the 2 separate flight records :
Flight in wooded area : https://www.phantomhelp.com/LogViewer/CDSJ96057OM98VKVTL9N/
In the hangar : https://www.phantomhelp.com/LogViewer/69YK32661KRA2RQWNHFO/

Has anyone had encountered similar issues?
Does anyone have an idea of why this is happening?
For info, I calibrated both the compass and the IMU but still issue persists.

Thanks for your help & support.

  • Lucie

First of all for this flight it is not surprising that some of the data was off. Flying indoors attempting to utilize GPS is never a good idea. Your Home point was set 371 seconds in to the flight and following that your NAV health dropped too low to be accurate. You will note the Distance calculations in the graph below are intermittant. The reason for all of the Obstacle warnings were due to the low ambient lighting.And as for this comment:

The only speed increase I see in this data is where you were applying elevator commands just prior to impact, along with the aileron where you state a sharp veer. Both of those inputs describe exactly what you saw. See Data Below:

Hello Fly_Dawg,

Thanks for replying.
Indeed I had noticed that home point was set during flight without instigation on my part. I guess that seeing that it assumes home point is set on ground level, it would go to minus readings if going below this point. Ok.

As for the second part, I noticed that the drone was pulling to the left and I was trying to rectify by going right but it kept deviating towards the left? Was this also because of combination of low ambient light and the Low NAV health?

There is no instigation on your part. Unless you manually re-set the home point, that point is determined upon sat lock. Your GPS reception was very weak indoors as you would expect.

Quite likely. If you notice in the posted graph, as I mentioned the last large “distance” spike. The aircraft did not know where it was. In addition notice the “GPS Used” data from the simple color graph below. It was False for the entire flight until the home point was established, then in and out for the remainder. Flying indoors should be done in ATTI manually to avoid sudden un-intended positioning swings.