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The Terminal Velocity of a Falling Mavic 2

Camino Ken

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#41
Very interesting. The three power-off events show similar initial evolution of pitch, roll and yaw, followed by varied, possibly chaotic, behavior:

View attachment 65882
View attachment 65883

View attachment 65884

The vertical speed reflects that, with a transition to oscillatory behavior as the aircraft wobbles:

View attachment 65885

View attachment 65886

View attachment 65887

The blue dotted lines are the model that I posted previously, with a slightly lower drag coefficient than my initial guess (0.025 rather than 0.031), and predict the motion pretty well. The terminal velocity of around 20 m/s (45 mph) is in line with previous data and reports.

I find this very fascinating. Some observations and/or questions.

It seems like the aircraft is tumbling randomly with the predominate motion of head over butt with a fair amount of yaw spin. Can I assume that the rapid changes are sign reversals or number overloads or is it actually flipping over in 100ms or less?

The negative motor speeds seem to indicate auto-rotation but why would it be constant; or is it just a data/math anomaly?

If this is too deep into the weeds let me know. My interest is purely intellectual.
 

sar104

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#42
I find this very fascinating. Some observations and/or questions.

It seems like the aircraft is tumbling randomly with the predominate motion of head over butt with a fair amount of yaw spin. Can I assume that the rapid changes are sign reversals or number overloads or is it actually flipping over in 100ms or less?

The negative motor speeds seem to indicate auto-rotation but why would it be constant; or is it just a data/math anomaly?

If this is too deep into the weeds let me know. My interest is purely intellectual.
Motor speed doesn't go negative - it's on the right axis. It goes to zero because the motors are off. I'm sure the props are turning in the air flow.

Here are the same data with the attitude values unwrapped (i.e. not constrained to -180 – 180):

unwrapped.png

I think it's fairly clear that the aircraft is rotating but not fully tumbling. It's rocking side to side and has some larger pitch excursions (which is on the unstable principle axis - i.e. neither the minimum not maximum moment of inertia), but it does not fully rotate - the motion is oscillatory.
 

Camino Ken

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#43
Motor speed doesn't go negative - it's on the right axis. It goes to zero because the motors are off. I'm sure the props are turning in the air flow.

Here are the same data with the attitude values unwrapped (i.e. not constrained to -180 – 180):

View attachment 65998

I think it's fairly clear that the aircraft is rotating but not fully tumbling. It's rocking side to side and has some larger pitch excursions (which is on the unstable principle axis - i.e. neither the minimum not maximum moment of inertia), but it does not fully rotate - the motion is oscillatory.
Thanks for the clarifications. Your right (you must get that a lot), I was looking at the wrong axis. Also, I was having trouble visualizing the overall behavior with the 180 shifts. This graph is much easier to understand. It looks a lot like one would expect, seems to be porpoising and rotating similar to a unbalanced flat object falling.

It would be interesting if someone could input this data into a drone flight simulator to visually recreate the behavior.

Thanks
 
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#44
Quick update -

The repair is covered under warranty! SUPER lucky considering I modified parameters and was flying in manual mode!

But now even more questions... Considering my extreme flight, what did DJI see exactly that made them determine there was absolutely a defect?
Was it this mysterious OTHER (8)? Or were simply the flight logs of the drone not recovering when switched into GPS/Sport mode enough to do it?
 

zxcflyer

New Member
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Jan 18, 2019
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#45
Very interesting. The three power-off events show similar initial evolution of pitch, roll and yaw, followed by varied, possibly chaotic, behavior:

View attachment 65882
View attachment 65883

View attachment 65884

The vertical speed reflects that, with a transition to oscillatory behavior as the aircraft wobbles:

View attachment 65885

View attachment 65886

View attachment 65887

The blue dotted lines are the model that I posted previously, with a slightly lower drag coefficient than my initial guess (0.025 rather than 0.031), and predict the motion pretty well. The terminal velocity of around 20 m/s (45 mph) is in line with previous data and reports.

Yes, it all starts very similar. It must be the CSC command (both sticks inside and down) that sets it on the backward downward spiral which later develops into chaotic fall.

Here is the video of the longest fall.
 
Last edited:
Likes: sar104

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