Crash during auto take-off

[MavicCF]

Maybe. But the aircraft DAT should have worked - there just isn't one for a flight at the time described. In fact not a single one of the DATs in that set was an actual flight.

Have you ever encountered an instance where the AC DAT failed to record? It seems like it should be a fairly infallible system.

 

[sar104]

Have you ever encountered an instance where the AC DAT failed to record? It seems like it should be a fairly infallible system.

Not that I recall.

 

[BudWalker]

Have you ever encountered an instance where the AC DAT failed to record? It seems like it should be a fairly infallible system.

Actually, this happens quite frequently to pilots using FW 01.03.0900 and after - myself included. As I understand it some .DATs get recorded on flash memory making them effectively non-existent to most people. I think there is a way of retrieving those .DATs but it requires a rooted Mavic and some advanced knowledge.

I've discovered how to keep .DATs from being recorded on the flash memory in the first place. Basically, the SD card is kept close to empty by periodically deleting the .DATs from the SD card. So far, all of my new flights get recorded on the SD card where I can get them. I've been doing this for a month or so and it has worked every time so far. My Mavic has been rooted but I don't think that matters.

Here's my method for deleting .DATs from the SD card.
1) Connect USB port to the PC and then start a FTP client (I use FileZilla).
2) connect to 192.168.42.2 with UserName = nouser, Password = nopass, port = 21
3) On the remote site (i.e., the Mavic) navigate to the /blackbox/flyctrl directory and delete the .DATs you don't want.

Just to be clear this method can't retrieve a .DAT recorded on the flash memory (so it won't help here). It only makes it possible to retrieve future flights.

 

[dbyantis]

Have you thoroughly checked the props? Motors? This behavior seems more hardware related than software.



Mike

Since the drone was flying over iron ore deposits, it is more likely a compass sensor getting thrown off, if the software cannot confirm the direction/orientation it cannot properly control the flight of the Mavic. Since the pilot used auto-launch, the drone was in complete control with bad data, unstable flight. The logs of the actual flight will show the compass condition.

 

[Tinmania]

Since the drone was flying over iron ore deposits, it is more likely a compass sensor getting thrown off, if the software cannot confirm the direction/orientation it cannot properly control the flight of the Mavic. Since the pilot used auto-launch, the drone was in complete control with bad data, unstable flight. The logs of the actual flight will show the compass condition.

Sorry, but I do not agree. If the aircraft behaved as described by the OP that is not a compass issue. Compass errors have of course caused flying in the wrong direction. But spiraling to a crash? I don’t think so.



Mike

 

[sar104]

Sorry, but I do not agree. If the aircraft behaved as described by the OP that is not a compass issue. Compass errors have of course caused flying in the wrong direction. But spiraling to a crash? I don’t think so.

Mike

I wouldn't rule it out - I've seen a couple of similar events where it was a compass error. If the error is close to 90° and the FC applies any kind of corrections immediately after takeoff (to correct for wind for example), then the resulting flight can spiral (literal meaning) out of control very rapidly.

 

[Mad Mavic]

I have a new Mavic Pro drone. After calibrating the compass and IMU I flew it successfully for the first time yesterday.

Today, after updating the firmware and Fly Safe databases I tried to fly the drone again in a location about 300 metres from the first location. The grass was a little long so I placed the drone on a large flat picnic table. I did all the pre flight checks and when the app showed "Ready to go" I tapped the takeoff icon and then slid the takeoff slider. The drone began to rise and when still low in the air it moved to the right and began to spiral back towards me. I tried to counter these movements with the controller but this seemed to have no effect and the drone quickly flew towards a bush and then hit the ground. The drone had a few grass stains but there appeared to be no damage.

I thought perhaps taking off from the picnic table had confused the sensors so I tried to fly the drone again from a small patch of ground without grass, using the same auto takeoff feature. The same thing happed again with the drone spiralling and flipping on to the grass. Again the drone seemed to be ok. I realised something was wrong and decided not to attempt another flight until I got to the bottom of the issue.

I then read some forum posts about similar incidents with replies suggesting IMU and compass calibration. I successfully calibrated the IMU but the compass calibration wouldn't complete with the app continuing to show the screen asking to rotate the drone horizontally.

The only differences to the drone from yesterday's successful flight were:

1. A different battery was used, which did not have a firmware update. (The battery used yesterday was in the drone when I updated the firmware.)
2. The propeller guards were fitted
3. DJI Goggles had been paired with the drone but were not used during the flights

I've uploaded the DAT file for the 2 flights here: Dropbox - DJI_ASSISTANT_EXPORT_FILE_2018-04-19_22-08-22.DAT

Any help in understanding what went wrong and what I should do next would be much appreciated.

Many thanks

hello Lengthlord, just curious if you have ever had a prop strike. The reason I'm asking is that I did and one of the small square ends of one the prop latching hooks brook off and fell down onto the top of the motor. I actually flew it once and didn't discover it until the second takeoff when it destroyed my gimbal. when it too fell off a table, landing on the concrete.

just guessing

 

[4wd]

I'd still suspect some metal under the wood on that table, and now maybe some physical damage from the two minor crashes.
I've had compass error sometimes from those tables with benches attached each side like one unit.
They don't all have metal rails underneath but some do.

 

[lengthlord]

hello Lengthlord, just curious if you have ever had a prop strike.

Hi Mad Mavic,

I've checked all the props. They all look fine with no cracks or breaks. All the latching hooks are still in place.

The drone has only flow 4 times. One demonstartion flight in the shop. One sucessful short flight, flown by myself, which was an auto take-off, hover, then up above the houses, took a couple of photos, then back down and auto land. Then the 2 crashes.

 

[lengthlord]

Would the tablet DAT work?

Maybe.

I've uploaded all the DJI GO 4 app documents for you guys.

 

[Tinmania]

I wouldn't rule it out - I've seen a couple of similar events where it was a compass error. If the error is close to 90° and the FC applies any kind of corrections immediately after takeoff (to correct for wind for example), then the resulting flight can spiral (literal meaning) out of control very rapidly.

When I think of spiral out of control, I don't think of a level quad just flying in different directions. I think of a quad flying off while spiraling at an angle that is anything but close to level. But perhaps the OP used that phrase differently than I would have.


Mike

 

[lengthlord]

When I think of spiral out of control, I don't think of a level quad just flying in different directions. I think of a quad flying off while spiraling at an angle that is anything but close to level. But perhaps the OP used that phrase differently than I would have.

My apologies for using confusing language, Mike. By "began to spiral back towards me" I mean the drone turned to it's right and droppped in height. It only made about a quarter or max half a turn.

As I recall during the first crash the drone moved about 5 metres to the right, dropped in height and hit a bush, then the ground. During the second crash it moved to the right, turned, rolled and dropped in height. In both cases the drone ended up on it's back with the propellers cutting the grass.

 

[lengthlord]

Would it be helpful if I upload the Black Box data from the drone and controller?

 

[sar104]

Would it be helpful if I upload the Black Box data from the drone and controller?

I found at least one of the offending flights in the set of txt logs. Still looking at it.

 

[MavicCF]

I found at least one of the offending flights in the set of txt logs. Still looking at it.

Which one was it?

 

[sar104]

Which one was it?

DJIFlightRecord_2018-04-19_[17-29-29]

 

[BudWalker]

DJIFlightRecord_2018-04-19_[17-29-29]

Also DJIFlightRecord_2018-04-19_[17-19-36].txt. They both look like textbook examples of launching from a geoMagnetically distorted site. But, that would be a huge coincidence. That and the fact that the OP can't calibrate the compass make it likely (to me at least) that it's broke and needs repairing.

 

[lengthlord]

Thank you for checking the logs

But, that would be a huge coincidence

Sorry, what would be a huge coincidence?

 

[sar104]

Thank you for checking the logs



Sorry, what would be a huge coincidence?

That both the takeoff locations that you used would have significant magnetic distortion.

 

[Mossiback]

If you are able to test in the same area; go back to the picnic table, turn on the Mavic, note that the direction Go 4 shows it is pointing is accurate, then pick the Mavic up away from the table and see if the indicated direction remains accurate. It seems that if rebar in cement can affect the compass then iron ore in the soil may also affect it.

I don't know if you can raise it high enough manually but you did mention that the fault occurred while still low in the air.