Mavic 2 Pro Flyaway

sar104 · Sep 18, 2018

ChopperLinc said:
My inexperienced opinion is that the aircraft suffered a power loss, although the FC crash is a possibility. Here’s why I think it lost power:

1). Sar104 calculated the trajectory based on it vector when the signal was lost and I found the drone literally in the exact spot indicated by his calcs.
2). If the FC crashed and the drone reset home point and landed, I think I would have seen it hovering. I was flying at night and have found it to be much more visible with the lights than in the daytime, and it was only 300 feet away. It was immediately invisible.
3). Signal loss seems extremely unlikely. In the short time I had it I did some non-scientific range tests. In one instance I was transmitting from between two high tension power transmission lines and the drone was a mile and half away. When I lost sight of it for a a few seconds, the video transmission became choppy. I increased altitude and it returned. You all have flown much longer than me, but signal loss seems to be gradual, not immediate and catastrophic.

I guess the FC crash could be a culprit, and the drone could have attempted to land, crash through some trees and happened to fall on the exact spot it would have if it lost power and fell from the last know height and speed...

FYI. When I recovered it, I replaced the battery which had fallen in the pool. Everything was all broken and banged up, include large parts of propeller missing...and it still flew perfectly (which I did for about 30 seconds in front of me in my living room.)

Just to clarify - if the FC crashes then the aircraft crashes - it doesn't just hover waiting for instructions.

ChopperLinc · Sep 18, 2018

sar104 said:
Just to clarify - if the FC crashes then the aircraft crashes - it doesn't just hover waiting for instructions.

Sorry, FC = Flight controller? Different than the RC unit my phone hooks up to?

sar104 · Sep 18, 2018

ChopperLinc said:
Sorry, FC = Flight controller? Different than the RC unit my phone hooks up to?

Yes - the FC is the flight controller on the aircraft.

ChopperLinc · Sep 18, 2018

sar104 said:
Yes - the FC is the flight controller on the aircraft.

Is it possible that the flight controller could have failed and then reset. Seems odd it would drop but then be flyable again after I recovered it.

sar104 · Sep 18, 2018

ChopperLinc said:
Is it possible that the flight controller could have failed and then reset. Seems odd it would drop but then be flyable again after I recovered it.

That's happened in other cases and is not unexpected. Just as with a regular computer it can crash and then work again after a reboot.

Goof · Sep 18, 2018

How long, in your experience does the FC take to reboot and recover the aircraft's attitude? Is it reasonable to then glean a minimum safe flying altitude to maximise chance of recovery should the FC crash mid-flight?

sar104 · Sep 18, 2018

Goof said:
How long, in your experience does the FC take to reboot and recover the aircraft's attitude? Is it reasonable to then glean a minimum safe flying altitude to maximise chance of recovery should the FC crash mid-flight?

You see the boot sequence every time you power up the aircraft. The M2 appears to take around 12 seconds to boot. These aircraft reach a terminal velocity of about 15 m/s in a few seconds, and so you would have to be at least around 200 m up to give it a chance.

RayOZ · Sep 20, 2018

sar104 said:
You see the boot sequence every time you power up the aircraft. The M2 appears to take around 12 seconds to boot. These aircraft reach a terminal velocity of about 15 m/s in a few seconds, and so you would have to be at least around 200 m up to give it a chance.

And you'll still need to give it the motor start command as it falls.

sar104 · Sep 20, 2018

RayOZ said:
And you'll still need to give it the motor start command as it falls.

Yes - my estimate did not explicitly include the time for that to happen but I added 50 m or so based on previously reported freefall tests showing that it took that kind of distance to restart the motors and arrest descent.

ChopperLinc · Sep 21, 2018

sar104 said:
Yes - my estimate did not explicitly include the time for that to happen but I added 50 m or so based on previously reported freefall tests showing that it took that kind of distance to restart the motors and arrest descent.

Will these autorotate or do they tumble?

Meta4 · Sep 21, 2018

ChopperLinc said:
Will these autorotate or do they tumble?

They don't autorotate

ChopperLinc · Sep 21, 2018

Meta4 said:
They don't autorotate

Then what’s the point of even discussing how long it takes to reboot? Won’t it most likely be in an unrecoverable attitude if it’s tumbling through the air?

laurens23 · Sep 21, 2018

ChopperLinc said:
Then what’s the point of even discussing how long it takes to reboot? Won’t it most likely be in an unrecoverable attitude if it’s tumbling through the air?

plenty of videos of it being done [youtube link]

WithTheBirds · Sep 21, 2018

laurens23 said:
plenty of videos of it being done [youtube link]

Are any of those a claimed recovery of a flight controller crashing and comming back on line? CSC and motor restart must have a higher chance of success.

ChopperLinc · Sep 21, 2018

laurens23 said:
plenty of videos of it being done [youtube link]

Interesting. Maybe lucky on attitude when recovered. Was not a full reboot though. Looks like CSC and prop restart.

sar104 · Sep 21, 2018

WithTheBirds said:
Are any of those a claimed recovery of a flight controller crashing and comming back on line? CSC and motor restart must have a higher chance of success.

They were all just CSCs. I was actually trying to point out that a reboot, motor restart and recovery was such a long shot that it was not worth factoring in to flight planning.

ChopperLinc · Oct 1, 2018

Update: After speaking to DJI customer care again, they have finally finished an analysis and agreed to replace the M2P due to a mfg defect.

Seems like there’s a bit of right hand/left hand communication disconnect as nobody has been able to tell me when I might receive the replacement, but at least it’s a step in a positive direction.

ruggb · Dec 23, 2018

Meta4 said:
The compass is the most misunderstood aspect of flying.
Forums (and even some DJI manuals) are full of myths.
It's completely unnecessary to recalibrate the compass or anything else before flying.
Whether you travel 10 miles or 2000 miles makes no difference at all.

NOT so much. If you want to bet your $1300. drone on that, go for it. The compass responds to magnetic fields and if some thng occurs to distort those fields, calibration may be required, or you may need to find another place to fly. This is a good thread on calibration
Compass Calibration Guide

Meta4 · Dec 23, 2018

ruggb said:
NOT so much. If you want to bet your $1300. drone on that, go for it.

My drones cost quite a bit more than that and go for it is exactly what I do.
I have a P4 pro that has had two full years of hard professional use and I've never calibrated anything on it.
I avoid launching from steel or reinforced concrete surfaces and have no problems.

ruggb said:
NOT so much. If you want to bet your $1300. drone on that, go for it. The compass responds to magnetic fields and if some thng occurs to distort those fields, calibration may be required, or you may need to find another place to fly.

Yes .. a compass responds to magnetic fields .. that's what a compass does.
If you place your compass in a non-normal magnetic field, the compass should warn you with what DJI mistakenly calls a compass error, but is more of a compass warning.
If your compass is warning you of a non-normal magnetic field, no amount of calibration will correct the problem.
Moving away from the problem is the only correct action.

ruggb said:
This is a good thread on calibration: Compass Calibration Guide

I haven't read the rest of that thread yet but the initial post, is very good.
You should read it again. (it had some incorrect information which was edited out later).

Just as a compass error isn't a fault that needs fixing, calibrating the compass doesn't make the compass more accurate or somehow "fix" errors.
Calibrating your compass, identifies and measures the magnetic fields that are part of your drone so they can be ignored to get a proper measurement of the magnetic fields outside of the drone when in flight.

sar104 · Dec 23, 2018

ruggb said:
NOT so much. If you want to bet your $1300. drone on that, go for it. The compass responds to magnetic fields and if some thng occurs to distort those fields, calibration may be required, or you may need to find another place to fly. This is a good thread on calibration
Compass Calibration Guide

It's a fine thread on calibration. It's unfortunate that you didn't read it before posting, because it supports everything that @Meta4 wrote.