Sudden gimbal movement (I thought "thats it, I'm going down")

[Just360]

Good day to you all,

I would like to ask your kind help to investigate this situation please.

I was above the lake and scared bunch of birds, they flew up (Yes, I should have expected that, but I didn't...) and I jumped into sports mode, raised the altitude and decided to grab few shots while I am evacuating the area at full speed. I grabbed few really good shots and at that time I thought I am reasonably safe. I flew back towards my home point, but thought will grab quick picture before landing - at this point I was above water. Then I suddenly saw a very strong gimbal movement - at that second I thought "thats it, I'm going down" + I was above water. After that sudden movement (it was fraction of the second gimbal moving down and to the side, after thinking about it, something I would expect if there would be a very strong wind gust pulling drone to the side and it trying to stabilise) gimbal got stable fraction of the second later and I landed immedietly after that.

Reviewing the flight reply in DJI Fly app, I believe that gimbal movement happened at around 5m 05sec of the flight, as after that, as I clearly remember, I got back down ASAP being super happy I still have my drone.

I really would like to understand if there was some issue with my drone, or I was just attacked by a bird, which I didn't notice. I would really be sceptical about wind gust, because I checked UAV forecast before flying an there was very minimal amount of wind, I remember calling it ideal conditions (sorry will not remember exact numbers).

Would really appreciate you help looking into data please.

Thanks,
Justas

 

[slup]

No, don't believe this was a sudden wind gust ... you had mainly a straight headwind where this happened. And it wasn't a gimbal shake either ... the whole AC turned nearly 60 degrees CCW and back during approx a second. Both IMUYaw, the Gyro & the magYaw registered the movement.

During the uncommanded yaw movement starting at 296sec. you had only pitch & roll sticks active ...



Instead I think this have to do with one of your rear props starting to be deformed ... looking at the time for the yaw movement the left rear are close to max rpm indicating not being able to generate proper CW torque, making the AC rotate CCW. About 297sec the right rear (CCW torquing prop) lower it's rpm to counter act the rotation & that brings the AC back CW to the original course.

My advise is to change your props, especially the left rear.

 

[Just360]

No, don't believe this was a sudden wind gust ... you had mainly a straight headwind where this happened. And ...

Hey Slup, thank you very much for this looking into this. This is awesome how much info you can get from these logs, amazing.
Replaced both rear props following DJI manual/tutorial.

60degrees sound a lot. Do you think I was close to loosing control of the aircraft?

Justas

 

[slup]

Hey Slup, thank you very much for this looking into this. This is awesome how much info you can get from these logs, amazing.
Replaced both rear props following DJI manual/tutorial.

60degrees sound a lot. Do you think I was close to loosing control of the aircraft?

Justas

Hard to say ... have seen this uncommanded yaw twitch earlier & then it have been in addition to an uncommanded descent due to that the deformed props (mostly the rear ones) also can't generate pitch according to spec & at worst, the AC lose lift and can't stay airborne any more. So flying over water when loosing lift ... yeah, this could have ended differently.

 

[Just360]

@slup, thanks got it. Did I get it right that 16k rpm is max, and in normal situation (not sure how to define normal) motors should not spin that fast, right? So basically, even going full throttle in sport mode should be far from 16k rpm? As I understand, I was flying full speed in sports mode most of the flight and rear left motor got to max speed when I was not moving fast at all.

Trying to understand the pattern so I could check for this anomaly again in my next few flights