A2 fly-away and crash

[BogotaMatt]

Hello guys, I'd like to share with you a fly-away that happened to us last week.
S900/A2, all up to date as per DJI bonkers update procedure.
Rehearsing a shot for the next day on location.
Compass calibrated, 14 satellites lock, IOC off and GPS mode.
Spool up, take off, copter at 2m, make sure everything is ok, then within 20s all control is lost, it doesn't respond to any radio input.
Upon seeing that the copter was not responding I immediately switched to ATTI then tried to failsafe even CSC, nothing worked.
We got very lucky that it didn’t hit someone as it overflew a busy road at low altitude.
We have a lot of shoots with this copter that never posed any problems before this.
Copter destroyed, we contact DJI and it become immediately clear that they will not play their part. We send the logs to the last 5 flights and the crash video their only response is we'll offer 20% on repairs.
Sweet, $4300 down the drain.
We're selling everything DJI-related and are moving on to a better alternative. I think this is the right place to find it.

 

[Hexacrafter]

Matt,
Understanding what happened will help prevent this type of occurrence, but blaming the MFG. until you can define the cause is really not helpful.... Sorry... MHO...
So I have seen and heard about this type of condition many times.... I do not have facts, so I will offer opinions based on your description....
1. Did you wait to fire up motors until the new homepoint was recorded?
2. Did you test for RFI interference at the new site?
3. Did you perform a new compass calibration at the new site?

Here is my theory of what happened.....
You are in GPS mode and took off before the A2 recorded a new homepoint...... so the failsafe/ RTH homepoint was the last recorded.... sometimes miles away.
After in the air, you lost radio connection to the aircraft forcing Failsafe/ RTH.
You tried to change modes to recover control, but since there was not a Radio connection it stayed in failsafe as it is designed to do and tried to fly home or hover at 20m depending on what you have configured.
You also flipped the switch to RTH so if the signal was regained it would still try to fly home...
so...
If the radio reconnected.... it was trying to fly home to a homepoint far away or
If the radio stayed disconnected... it was trying to fly home to a homepoint far away.

The two big errors I have seen when it comes to fly away conditions are usually based on the above conditions or a mix of them.
Many like to take off in ATT mode as that is what they fly, but without a recorded new homepoint, the failsafe can only fly to the last recorded position.... or those that fly in GPS at take off but do not wait for a new homepoint to be recorded have the same failure.

I do not mean to sound unsympathetic, and am sorry for your losses, but when all of the facts are available, there is usually a reasonable explanation for aircraft crashes.....
I hope this is helpful...

 

[BogotaMatt]

I appreciate your reply but, the copter was powered up a good 5' before engine start as I performed compass calibration then had a small chat with my operator who was setting up his screen etc. I distinctly remember looking at the sat count and seen 14. I have not checked for Rfi interference but we have flown countless times there wether with the S900 or a Phantom without a single problem. The lost radio connection 2m away from the copter I don't really buy it and in case of a flight back to the last recorded point it would have flown to the exact opposite as it was right next to my house where I flew the day before.... Crashes do happen and I'm not blaming DJI's equipment. I'm blaming their refusal to examin log files and basically hide behind the fact that it can also be an equipment fault... I have the log file from that file if you'd like to see it...

 

[Hexacrafter]

Sure...
Post the file.
It is helpful to see data....
Fired up does not mean it recorded a new homepoint.....
Only watching for the rapid flashes can confirm that it is recorded.
Have you checked batteries in TX? I have "charged" my TX and gone to fly and had radio failure right in from of me......... come to find out that the batteries were not taking a charge... Now my pre-flight checklist includes checking TX voltage... like lipo voltage on the aircraft...
I am curious to see how the Forum may comment on a MFG. reviewing flight logs after a crash....
I know of no MFG. that will do this..... too much liability.....
Perhaps the cause can be determined... I prefer that.....
Sometimes it stays a mystery..... those cause many sleepless nights...

 

[cootertwo]

I don't think you'd have as many problems with log files from a 3DR product. Just sayin...........

 

[BogotaMatt]

All the batteries are charged and checked prior to every flight. I was an airline pilot for 15 years and have a pretty strict routine before taking off. We're at the equator so we usually have a fantastic GPS cover, rapid flashing it was before take off. The gimbal erratic movements make think of an IMU failure.
Here's the log : http://we.tl/hoV25Hxx68

 

[Hexacrafter]

U Channel & IOC active at 22 sec...
I assume you have RTH set to U Channel.... with IOC set to return forward or backwards....
If this is the case....
It went into failsafe.....
Either by loss of TX or by some other means....
View attachment 25666

 

[BogotaMatt]

Yes that corresponds to the loss of control. I went GPS-Atti then radio off to trigger failsafe. This is a fantastic discussion and I'm glad I joined this board.

 

[Hexacrafter]

All three happen at the same time 21.683 sec...
1. Flight mode goes from Manual to GPS
2. U- Channel Failsafe Initiates
3. IOC switches on.

As soon as it gets a GPS lock it is in failsafe & IOC....
I bet with a home point other than where it was taking off from...
and trying to fly home.
Sorry.
View attachment 25667

 

[BogotaMatt]

I appreciate your analysis, still weird that it would take so long to get a lock....

 

[dazzab]

Isn't the home location recorded in the log? Although I fly with DJI FC as well, I think it should be a requirement for flight controllers to provide full logging of all parameters and flight details. It's the only way you can do forensics. That information is probably in the logs but only DJI can access it. I wonder what they are hiding?

 

[BogotaMatt]

I would think so, but the GPS icon on the DataViewer never worked for me so I don't know... I would assume, then we could see if the home point recorded for my crashed differed from the actual location, because my home is the opposite to where it flew to...

 

[Carapau]

Home point in the A2 is recorded as you throttle up for the first time on each flight so it should have recorded. If it didn't then this would be a fault within the FC.

 

[BogotaMatt]

Would the coordinates be shown on the flight log ?

 

[Hexacrafter]

Cara...
Homepoint can only record if GPS signal is strong enough....
The log shows 6 satellites at the time of spool up and this incident.
One thing I learned a long time ago is not to rely on what is supposed to occur, but rather what is confirmed to occur.
If one wishes to rely on a recorded homepoint then waiting to see the visual rapid green flashes is the only confirmation.....
If GPS signal is not strong enough.... then .... no homepoint... & NO GPS RTH help....
This has been my experience.
Also.... No.... DJI does not include a recorded homepoint as part of the user accessible Data from the iOSD file.

 

[BogotaMatt]

I took off with 14 satellites shown on the IOSD that's very weird...

 

[Pumpkinguy]

I'm following along in hopes to learn from this unfortunate event. So it appears he didn't have home lock but what could be the reason for a loss of control link? The op didn't say his transmitter went dead.

 

[BogotaMatt]

Transmitter didn't go dead, copter went crazy, and that's were I'm kind of dubious about the copter behavior, if it tried to go home, say at my house, where the last recorded would have been, it doesn't explain why it went to the opposite at full tilt then crashed in a nearby parking lot. The flight path makes no sense to me.

 

[Pumpkinguy]

You never mentioned what rx tx you were using. Just to satisfy my curiosity were you using internal reciever, sbus reciever or satillites?

 

[BogotaMatt]

I use 2 14SG, one on the A2 receiver the other on a Futaba receiver for the Z15. I've never had any problem with this setup, ever.