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Crash during auto take-off

lengthlord

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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
 
Last edited:

TrayBoz

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Was the picnic table metal?
Did you calibrate the compass on or near the picnic table?
Try recalibrating the compass well away from any metal (including any metal rebar in concrete) - watch some YouTube videos on proper method if you're not 100% sure you're doing it right.
Remove the prop guards and try to launch without them to see if they are the problem/ installed incorrectly.
I don't think the battery or goggles could be causing that kind of behavior. Sounds like compass/IMU or prop guards.
 

sar104

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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

There are four DAT files in that set, 34 - 37, but none of them is an actual flight.

FLY037 was a 90 s power up timestamped 2018-04-19T20:25:30Z.
 

lengthlord

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Was the picnic table metal?

Thank you for your reply and advice. It is a wooden picnic table. The hill where I tried to takeoff is called Paddock Mound and is man made. There is a sign by the mound that mentions that the mound is made from clay, and built on top of a capped mine shaft. I've just found this web page, that says the mound "was formed by coal and iron ore working in the 18th century". Anyway the DJI GO 4 app didn't prompt me to calibrate the compass.

Did you calibrate the compass on or near the picnic table?

I calibrated the compass the day before in a different location, only a few hundred metres away. The drone flew perfectly after the calibration. After the crash, when I tried to re-calibrate the compass I was on the mound. The only metal object nearby was a different picnic table about 10 metres away.

The Disclaimer and Safety Guidelines is a little confusing about compass calibration. Under Safety At a Glance - 2. Pre-flight Checklist on page 4 it writes "Only calibrate the compass when the DJI GOTM app or the status indicator prompt you to do so". Then on page 7 under another section titled Pre-flight Checklist it states "Follow the on-screen instructions to calibrate the compass".

Should I calibrate the compass before every flight, or just when prompted by the app?

watch some YouTube videos on proper method if you're not 100% sure you're doing it right.

Thank you that's a good idea I will watch some videos because I'm not totally clear if I'm doing it correctly, although the drone did fly perfectly after my first calibration.

Remove the prop guards and try to launch without them to see if they are the problem/ installed incorrectly.

I'll try flying again without the prop guards. I’d be very glad if someone had a look at the logs beforehand. I'm pretty sure I installed the guards correctly. I watched this DJI quick tip video before installing them.

I don't think the battery or goggles could be causing that kind of behavior. Sounds like compass/IMU or prop guards.

Good to know, thanks :)
 
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sar104

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Thank you for looking at the DAT file. I uploaded the 2 files with the most recent date. How do I know which are the correct files?

DJI Assistant screen shot

I've uploaded all of the DAT files to this Dropbox folder.

Still missing the flight in question. These are the timestamps for 30, 32 and 33, which were also power up events but not flights. What time was your flight? FLY031 is not in the set.

FLY030: 2018-04-19T16:43:54Z 800 s, no motor start.

FLY032: 2018-04-19T17:04:00Z 1100 s, no motor start.

FLY033: 2018-04-19T17:22:47Z, no motor start.

Prior to that there are no real flights.
 

Tinmania

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The drone began to rise and when still low in the air it moved to the right and began to spiral back towards me.
Have you thoroughly checked the props? Motors? This behavior seems more hardware related than software.



Mike
 

lengthlord

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There are four DAT files in that set, 34 - 37, but none of them is an actual flight.

FLY037 was a 90 s power up timestamped 2018-04-19T20:25:30Z.

Thanks for looking again at the files. I will try again to download them form the AC. Which app should I use to check which flight IDs I’ve downloaded?

Would it be helpful if I also upload the Back Box data logs?
 

lengthlord

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



Mike

Thanks Mike, I’ve visually checked the props and these seem fine, even after the crashes. What’s the best way to test the motors?
 

lengthlord

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What time was your flight?

The 2 flights when the drone crashed, one shortly after the other, were at around 18:30 UK time on Thursday 19th April 2018.

I have not flown it since but I have powered it up.
 
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Mavflyer

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If you lose a prop, or if a motor quits working or slows to a speed slower than it should, this will cause a spin/spiral and a rapid decent. This happens because the spinning props will cause torque in the opposite direction of the spin. If you lose a prop or motor speed, you will basically have two pushing the yaw in one direction and one pushing in the other, a losing battle. Did you pay attention to which direction it spun? You could narrow it down somewhat if it is in fact a motor, esc, or prop issue.
 

Mavflyer

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It moved to its right and span anti-clockwise, but only about a quarter or half a turn, dropping in height until it hit the ground. About 1.5 metres max.
Doesn't sound like a bad motor. It would have spun way more than that.
 

sar104

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I've exported the data again. This time I used Select All before exporting ;) Here's the new DAT file, and here's a screen shot of the Data Upload List.

Sorry - I can't find any flights in there - the DAT files seem to be a mixture of firmware upgrades and power ups - no motor starts in any that I have found. The time that you mentioned (1830) is presumably 1730Z on April 19. That should be FLY033, 34, 35 or 36, since 37 was at 2025Z. But 33 has not motor start, and 34/35/36 don't even have a GPS lock to get a timestamp. Very puzzling.
 

MavicCF

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Sorry - I can't find any flights in there - the DAT files seem to be a mixture of firmware upgrades and power ups - no motor starts in any that I have found. The time that you mentioned (1830) is presumably 1730Z on April 19. That should be FLY033, 34, 35 or 36, since 37 was at 2025Z. But 33 has not motor start, and 34/35/36 don't even have a GPS lock to get a timestamp. Very puzzling.
Would the tablet DAT work? Glad I didn't even try to download those ones:).
 
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