Mavic Pro Fly Away with Litchi

[kayest]

After over 100 trouble free flights, I had my first fly away. Switched from Go to Litchi and this was my 4th flight with Litchi. Powered up on a concrete sidewalk, saw no errors and took off. Almost immediately I lost control. Mavic did not seem to be responding to sticks but it was over so fast I am not sure. The only thing I noticed on the Airdata replay was the aircraft is shown facing north east when in fact it was facing (and flying) south right after takeoff. Problem is, I saw no indication of a compass error.

I would greatly appreciate any insight anyone might have. My log:

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[Prismatic]

I'm 98% sure that the more qualified analysts on the forum will find that you launched in a magnetically compromised location. It was most likely caused by rebar in the concrete at the launch point.

Whatever the cause, the compass was initialized with an error of something like 135°. The flight control system (FCS) believed the aircraft was facing northeast when the true bearing was south. Therefore, the FCS could not correctly apply stabilizing thrust.

For example, suppose you just tried to hover for a moment after launching. If air currents push the drone a bit SW (i.e. 'backwards' in the view of the FCS), the FCS naturally counters with forward thrust, expecting to move the drone NE toward its hover-location.

But because the aircraft is actually facing S, forward thrust takes the aircraft even farther from the hover-location. The FCS interprets this undesired change in position as due a slightly stronger wind, and applies additional forward thrust, making the situation worse.

In cases like this, the errors quickly compound, and the drone speeds away, out of the pilot's control. (When the compass error is other than 180°, the drone's path is actually a spiral.)

To avoid this sort of flyaway, you need to verify that the aircraft symbol on the map is oriented as in reality--regardless whether you're using Go4 or Litchi or whatever. That is, if the aircraft is pointed south on the ground, but the map shows it pointed northeast, you must not launch: to do so assures disaster.

I hope you were able to recover it without major damage. ?

 

[Meta4]

The only thing I noticed on the Airdata replay was the aircraft is shown facing north east when in fact it was facing (and flying) south right after takeoff. Problem is, I saw no indication of a compass error.

You saw no compass error because the magnetic field strength of the steel reinforcing in the concrete wasn't strong enough to set off a compass error.
But the difference between north and what your drone initialised to was enough to cause a Yaw Error situation just like many others in the past.
Launching from reinforced concrete surfaces won't always cause this, but it has happened so often that it's wise to avoid it.

 

[Fly Dawg]

After over 100 trouble free flights, I had my first fly away. Switched from Go to Litchi and this was my 4th flight with Litchi. Powered up on a concrete sidewalk, saw no errors and took off. Almost immediately I lost control. Mavic did not seem to be responding to sticks but it was over so fast I am not sure. The only thing I noticed on the Airdata replay was the aircraft is shown facing north east when in fact it was facing (and flying) south right after takeoff.

Unfortunately Litchi's flight data is very limited. The .dat from the aircraft would be helpful. Assuming this is an MP1......
In the interim, it appears as though the aircraft was responding to your controls, but some of these numbers do not look correct to me. Let me ask this question. Have you re-calibrated your remote? The max inputs look a bit off.....

 

[Cman]

is the side walk considered reinforced concrete?

 

[Thomas B]

is the side walk considered reinforced concrete?

Of course it may vary, but avoiding it will solve problems before you have them

 

[Prismatic]

is the side walk considered reinforced concrete?

In most of North America rebar (or steel mesh) are so common in concrete you should just expect them, and double check the map before takeoff.

 

[MAvic_South_Oz]

is the side walk considered reinforced concrete?

Usually yes, there is steel mesh and / or rebar.
I have taken off from sidewalk (we call them footpaths here ) without issues, but usually now if I have no choice of where I'm standing, I'll hand launch.

The most important thing to avoid this is check the little map and the orientation of the aircraft is the same to the ground before starting up the motors.

So many reports like this on flyaways on this forum, often 180 degrees out, aircraft tries to correct in the air, goes the way it THINKS it should, but this is the opposite way.
I believe the 2 compass discrepancy will eventually correct itself, from recalling previous thread comments, but quite often it flies out of signal range before anything can be done.

So for the OP, you said you had a flyaway, did you lose the aircraft ?
Or did you manage to get control again and recover ?

 

[Meta4]

is the side walk considered reinforced concrete?

 

[kayest]

Thank you all very much for the thoughtful analysis. I learned 2 key points. 1) Sidewalk may have rebar (I had always considered it a safe take off platform). 2) Always check the aircraft icon's heading before take-off. I kind of knew that it was the proper procedure but I got out of the habit. Expensive lesson but it could have been worse. There were cars in the parking lot. I missed them. I recovered the MP1. The camera and gimbal are totaled, the internal cooling fan is not running and lost 3 props. Not sure if worth fixing.

@Fly Dawg I don't believe I have ever calibrated the R/C. I will look into that. If you would like to look, I can try to pull the dat file. With no fan the MP1 gets very hot very fast. Just curious what additional information it has?

 

[Fly Dawg]

I will look into that. If you would like to look, I can try to pull the dat file. With no fan the MP1 gets very hot very fast. Just curious what additional information it has?

Even the .txt file from GO has more data than the .csv Litchi files. The aircraft .dat has most all the data available. IMU info, etc..etc...
in much detail. If you want to pursue that, it is your choice. You could use an external fan while collecting the files.