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Damage to trailing edge of propellers
765 12 2018-3-19
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djiuser_gj5u1EqP7rJe
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New Zealand
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We had our Phantom 4 Pro fall out of the sky while using Drone Deploy. It had reached the flight heigh (120m) and was on its way to the first waypoint with full battery.
Halfway to the first waypoint the app crashed while we were not looking at the drone, we then looked up and it had fallen to the ground and the battery was a couple of metres away.
It was sent to DJI for investigation but they did not report anything useful and it was not worth hassle of chasing them.

Interestingly two of the props had significant damage to the trailing edges. (Although the damage seems to indicate that it hit the ground feet first as two legs were squashed up a bit and the camera pushed into the body a bit).

How does a prop get damaged on the trailing edge?
It must go backwards surely? How could this happen?

About 4yrs ago I had a Phantom 2 V+ fall from 80m after flying for a couple of mins just while hovering, and I found 1 prop undamaged about 30m from the drone. I used the prop for the next year or more without incident. I have no idea how the prop come off.
It would have had to go backwards, wouldn't it?

I look forward to hearing your ideas.

Cheers
Caleb
2018-3-19
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HedgeTrimmer
Captain
United States
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"damage seems to indicate that it hit the ground feet first"
"How does a prop get damaged on the trailing edge?  It must go backwards surely? How could this happen?"

It's late, thus I may be reverse thinking this.
If prop motors were to loose power (battery failure, drone CPU turned power off); assuming drone fell staying upright - wouldn't props start to rotate backwards (reverse of normal lift direction)?

2018-3-19
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DJI Susan
Administrator

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Hey Caleb, sorry for the late response. May I have your case number? I'd like to check the current status and see whether we can help.
2018-3-21
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Nigel_
Captain
Flight distance : 388642 ft
United Kingdom
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For the P4, HedgeTrimmer is correct, on loosing power the drone will drop correct way up, the propellers will spin up backwards and it will hit the ground feet first with the props going quite fast.  There is not much inertia in the props so if unpowered I wouldn't expect much damage, but the trailing edge is a lot more delicate than the leading edge.  If dropping from 120m, the props will be spinning backwards at full speed long before it reaches the ground, the body will also be spinning at a fair speed which maybe where some energy to damage the props came from.

For the P3, no it wouldn't need to go backwards, only backwards relative to the motor, if the motor decelerates rapidly and the prop doesn't then the prop unscrews.  Normally it would screw back on before coming fully off but a sudden movement or gust of wind might help it come fully off.
2018-3-21
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ALABAMA
Captain
Flight distance : 10442687 ft
United States
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Did dji tell you what their analysis of the flight data indicated?
2018-3-21
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djiuser_gj5u1EqP7rJe
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New Zealand
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Our DJI agent (Ferntech) passed on this reply from DJI:

1. The aircraft worked in Tripod mode and responded to the pilot's command well;
2. T=02:40, H=3.3 m, D=19.9 m, battery 91%%, ultra height was 3.7 m, the attitude of aircraft was normal, then the record ended. The Last point: -42.3609820,171.4154453.
With the record ended without any sign of abnormality, we could not verify what happened afterwards.


That was all I got! The flight DJI was talking about was for a flight the day before the crash (I can tell from the GPS coordinates). So they didn't seem to actually investigate the flight that crashed (that log may not have saved) or any of the prior 10 filghts of that day! I wasn't very impressed.

2018-3-21
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djiuser_gj5u1EqP7rJe
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New Zealand
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Nigel_ Posted at 2018-3-21 04:49
For the P4, HedgeTrimmer is correct, on loosing power the drone will drop correct way up, the propellers will spin up backwards and it will hit the ground feet first with the props going quite fast.  There is not much inertia in the props so if unpowered I wouldn't expect much damage, but the trailing edge is a lot more delicate than the leading edge.  If dropping from 120m, the props will be spinning backwards at full speed long before it reaches the ground, the body will also be spinning at a fair speed which maybe where some energy to damage the props came from.

For the P3, no it wouldn't need to go backwards, only backwards relative to the motor, if the motor decelerates rapidly and the prop doesn't then the prop unscrews.  Normally it would screw back on before coming fully off but a sudden movement or gust of wind might help it come fully off.

Thanks for that Nigel. I hadn't thought of the up-draft causing the props to go in reverse.
Problem solved.
Cheers.
2018-3-21
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ALABAMA
Captain
Flight distance : 10442687 ft
United States
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djiuser_gj5u1EqP7rJe Posted at 2018-3-21 10:29
Our DJI agent (Ferntech) passed on this reply from DJI:

1. The aircraft worked in Tripod mode and responded to the pilot's command well;

I think you should press your case a little harder.  It is a hassle, but that's an expensive piece of equipment to replace.
2018-3-21
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djiuser_gj5u1EqP7rJe
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New Zealand
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ALABAMA Posted at 2018-3-21 10:57
I think you should press your case a little harder.  It is a hassle, but that's an expensive piece of equipment to replace.

I hear you. Here's the repair list, it cost $781NZ ($560US).
Lens Front Shell (With Shielding Cover)
Fan Module
Roll-axis Bracket V03
Lens
Phantom 4 Yaw-axis Motor
Middle Frame
Lens External Ring (With Filter)
Gimbal Flexible Flat Cable
Left Landing Gear Module
Lower Cover
Gimbal Yaw-axis & Roll-axis ESC Board
Ultrasonic Module
Upper Cover (Logo)
Pitch-axis Motor
Gimbal Vibration Absorbing Board
Rear Camera Cover
Phantom 4 Roll Motor
Roll-axis Back Cover
Main Controller
Yaw-axis Motor Cover
Pitch-axis Bracket V03
Phantom 4 2312S Motor (x2)
Right Landing Gear Module
Yaw-axis Cable Cover

It sounds like almost everything but at the end of the day quite a bit cheaper to repair.
2018-3-21
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Nigel_
Captain
Flight distance : 388642 ft
United Kingdom
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djiuser_gj5u1EqP7rJe Posted at 2018-3-21 11:02
I hear you. Here's the repair list, it cost $781NZ ($560US).
Lens Front Shell (With Shielding Cover)
Fan Module

That is a big list, normally from that high the propellers are fairly effective as a parachute once they have spun up backwards.  Did it hit concrete or something else hard?
2018-3-21
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djiuser_gj5u1EqP7rJe
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New Zealand
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Nigel_ Posted at 2018-3-21 13:26
That is a big list, normally from that high the propellers are fairly effective as a parachute once they have spun up backwards.  Did it hit concrete or something else hard?

Yes it hit some hard ground with some small rocks around. The attached image shows the drone, but not exactly where it crashed, I was not on site.
20180119_123645 (Large).jpg
2018-3-21
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Jeff Millard
First Officer
Flight distance : 503635 ft
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United States
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djiuser_gj5u1EqP7rJe Posted at 2018-3-21 13:44
Yes it hit some hard ground with some small rocks around. The attached image shows the drone, but not exactly where it crashed, I was not on site.

The saddest picture I've seen today. Poor P4. Get well soon.

Jeff
2018-3-21
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djiuser_AJmEIlf6kr6y
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Israel
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Did you eventually found the reason for the crash?
I had exactly the same problem last month..
1-24 03:39
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