Fell From the Sky--Prop Spun Off?

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I have some of those hairline stress cracks. Not sure if that has anything to with this but I doubt it. I had already called DJI and told them about the cracks, which the support rep insisted was cosmetic and does not effect flight. I was also having a problem artifacts/ripples in my videos, which I shoot in 1080P. So, getting pushback on the cracks I filled out a ticket online.

The shipping tag for me to send the P3Pro in showed up in my email this morning. I thought I'd take a quick flight at 4K to see if I still had video problems. I flew up into a grassy field and was hovering next to an old grain silo since there's a lot of graffiti in it and would be a decent test of the camera detail and anonalies. 2:57 into the flight my video feed tilted to 90 degrees, then went black, then I got a compass error ... and that was that. According to HealthyDrones I was 143 feet higher than my takeoff point. I estimate the hill I was over to be 20 feet higher than that takeoff point, making the drop about 120 feet into grass and damp dirt.

I went up into the field and retrieved the drone. I've seem a few Youtube videos wherein drones have crashed and magically, they fly again! Yeah, this one may fly again as is but it's not going to shoot any video for a while. Three props are damaged and one disappeared altogether. I'm guessing it spun off during flight, which seems to defy physics, based on the direction of rotation--unless the rotor stopped abruptly, in which case it probably landed somewhere in the next county, Newton's Third Law and all.

I tried calling DJI 20 minutes before their posted support-closing time and got a recording saying they are experiencing technical difficulties so they aren't answering the phones. My phones always go down they day before a long weekend. Don't yours?
 
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Meta4

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I have some of those hairline stress cracks. Not sure if that has anything to with this but I doubt it. I had already called DJI and told them about the cracks, which the support rep insisted was cosmetic and does not effect flight. I was also having a problem artifacts/ripples in my videos, which I shoot in 1080P. So, getting pushback on the cracks I filled out a ticket online.

The shipping tag for me to send the P3Pro in showed up in my email this morning. I thought I'd take a quick flight at 4K to see if I still had video problems. I flew up into a grassy field and was hovering next to an old grain silo since there's a lot of graffiti in it and would be a decent test of the camera detail and anonalies. 2:57 into the flight my video feed tilted to 90 degrees, then went black, then I got a compass error ... and that was that. According to HealthyDrones I was 143 feet higher than my takeoff point. I estimate the hill I was over to be 20 feet higher than that takeoff point, making the drop about 120 feet into grass and damp dirt.
Healthydrones doesn't show any actual flight data and it's next to useless for investigation an incident..
Where it shows a compass error isn't. It's the Phantom tumbling in the air.
To see what was really happening and maybe solve the mystery,
Go to https://www.phantomhelp.com/LogViewer/Upload/
Follow the instructions to upload your flight record.

Come back and post a link to the report it provides and someone here might be able to analyse it and give you an understanding of the cause of the incident.
 

Mark The Droner

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If you approached the crash site and one prop "disappeared altogether", then I think it's safe to conclude it spun off during flight. The question is why? Did it spin off because you didn't install it properly? Or did it spin off for some other reason...
 
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Healthydrones doesn't show any actual flight data and it's next to useless for investigation an incident..
Where it shows a compass error isn't. It's the Phantom tumbling in the air.
To see what was really happening and maybe solve the mystery,
Go to https://www.phantomhelp.com/LogViewer/Upload/
Follow the instructions to upload your flight record.

Come back and post a link to the report it provides and someone here might be able to analyse it and give you an understanding of the cause of the incident.


Thanks for the tip. The last two entries say "Speed Error." Since the log shows my speed as 6.4 mph I assume it's referring to a rotor, as I suspected. Worth noting that I dropped 13 feet in the .6 seconds between the messages. I think this one's on DJI. Phantom Log Viewer - PhantomHelp.com

And here's the HealthyDrone version, FWIW: HealthyDrones.com - Innovative flight data analysis that matters
 
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If you approached the crash site and one prop "disappeared altogether", then I think it's safe to conclude it spun off during flight. The question is why? Did it spin off because you didn't install it properly? Or did it spin off for some other reason...

Based on the final two log entries showing "Speed Error" I'm going to go with Newton's First Law. The rotor halted and the prop continued to spin, right off. I bet it went well over 400 feet, too.

I'll go up into the field tomorrow and see what I can find. When I went up there to retrieve the drone I did not do a thorough inspection of the area. I was admittedly a bit miffed. I picked up the drone and the gimble/camera assembly which was about five feet away, and brought it all home.
 
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I am almost positive DJI refuses warranty claims on prop spin offs since it is 100% pilot error. They need to be tightened down.
 
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I am almost positive DJI refuses warranty claims on prop spin offs since it is 100% pilot error. They need to be tightened down.

The log shows a "speed error." I don't know if the prop spun off or not but if it did it's because the rotor had a speed problem. The props were tightened by hand.
 
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The log shows a "speed error." I don't know if the prop spun off or not but if it did it's because the rotor had a speed problem. The props were tightened by hand.
The speed error was a result of the prop flying off. When there is no prop, the motor speeds up way faster than the other motors because the is no resistance from the propeller.
Not the reverse. The motor did not speed up, then the prop flew off.
This will be shown in the flight logs. It will show the speed of each individual motor, the motor missing a prop will show a spike just before the speed error message.


Sent from my Pixel XL using PhantomPilots mobile app
 

Mark The Droner

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Your lateral speed drops to zero at the end of the log which is a clue that the active braking engaged. That's what would cause a prop to spin off seemingly "defying physics." It would be fine if the prop was installed and torqued adequately. If the prop was installed improperly, there's a risk of spin off

We also see a slight increase in voltage as it drops in altitude at the end. That's another clue a prop was missing since load on the battery decreased.

Yes, a motor that abruptly stopped could also increase the risk of a spin off, but it's still not likely if the prop was installed properly. Also, these motors don't just stop or freeze up. They don't do that. So it seems unlikely.

Even though I install my props correctly, I had a prop spin off at 400' about seven weeks ago and I know it was my own **** fault since I didn't snug up the props before that particular launch.

Let's see what others have to say.

Sorry for your loss.
 
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it's hard to tell from the TXT log if the propeller is to blame
in the last second of the flight, OSD.isNotEnoughForce changed from false to true and also there is SpeedErrorLarge with that "Magnetic Filed Interference. Exit P-GPS Mode" warning
OSD.isPropellerCatapult and HOME.isWingBroken are both false all the time

if you can get DAT file out of the drone and convert it to csv with DatCon, rpm of the motors is visible there, so I think it will be easier to find out, if propeller went off or not
 
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The speed error was a result of the prop flying off. When there is no prop, the motor speeds up way faster than the other motors because the is no resistance from the propeller.
Not the reverse. The motor did not speed up, then the prop flew off.
This will be shown in the flight logs. It will show the speed of each individual motor, the motor missing a prop will show a spike just before the speed error message.


Sent from my Pixel XL using PhantomPilots mobile app


Well that makes sense that a prop flyoff would overspeed the rotor. What doesn't make sense is that the prop would spontaneously fly off at 2:56 into a stable flight. There always has to be a cause for something to change its speed of direction. The drone was hovering from 2:50 to 2:54.9. Five seconds at zero horizontal speed. A second before the speed error the speed increased to 3.7, I assume as the problem was developing and it hit a speed of 6.7 mph on the second speed error entry a second and a half later while on its way down. This drone has logged well over 100 miles so it's not like I've never put on a prop before. I have done some heavy duty breaking in the past--going from 35 mph in one direction and immediately reversing course to 35 mph. This was not one of those events. The aircraft was in a hover. Physics doesn't work spontaneously.

How do I get at the flight logs?
 
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The log shows a "speed error." I don't know if the prop spun off or not but if it did it's because the rotor had a speed problem. The props were tightened by hand.
Do not believe these guys about "Active braking" . There is a popular misconception here on these forums that the drone somehow stops or reverses or almost stops the propellars to slow down, when it actually simply tilts opposite of the direction it is going and applies MORE prop speed. Think about it. The drone moves by tilting one direction or the other. Slowing or stopping the props would get you NOTHING. It is not like reversing your prop on a boat to slow down/stop or the variable pitch prop on an aircraft engine.
 
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Do not believe these guys about "Active braking" . There is a popular misconception here on these forums that the drone somehow stops or reverses or almost stops the propellars to slow down, when it actually simply tilts opposite of the direction it is going and applies MORE prop speed. Think about it. The drone moves by tilting one direction or the other. Slowing or stopping the props would get you NOTHING. It is not like reversing your prop on a boat to slow down/stop or the variable pitch prop on an aircraft engine.

Yep. I agree. Just like a helicopter or a variable pitch prop on an airplane. It's all about blade angle of attack, taking a bite out of the air and variances then rotor speed, but a properly working rotor does not reverse direction. Two quad rotors go clockwise/two go anti-clockwise. Always.
 
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Flyer. Thanks. Without getting into a bunch of tech stuff, these things move by tilting, which diverts some downward thrust off to the side. To achieve braking / reverse direction, the tilt angle is reversed. In actuality, if the motors could be stopped or reversed, it would stop, maybe, but it would for sure fall out of the air. Your situation sounds like simply a failed prop or motor or motor driver. The design of the spin on props tends to tighten them over time, and when I have changed mine they were much tighter than I installed them.

FWIW these little motors are small permanent magnet armature three phase stator motors driven by a little DC to 3 phase AC converter. This allows the flight control logic to control speed and torque of each motor.
 
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Yes, not only do you and I agree that the props continue to tighten while the rotors are turning but so does DJI. I am on the /service/repair site now filling out a ticket and their own description for the props is "Phantom 3 9450 Self-tightening Propeller (1CW+1CCW)." The only way I can comprehend a prop flying off is a rotor malfunction or logic malfunction causing the rotor to rapidly decrease its spin--especially when the drone has been hovering for 4.9 seconds.
 

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Yes, not only do you and I agree that the props continue to tighten while the rotors are turning but so does DJI.
DJI has recommends tightening the Phantom props in the P3S manual:

TightenProps.png
 
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Got a bit of good news just moments ago from DJI. They're determined that this one is on them and will be repairing the drone at no charge. I should have it back by this time next week. So this weekend starts with good news and next weekend starts with flying.
 
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Great news. Glad it all went well. Any chance of uploading the footage of the drone falling. Will make great viewing

Neon Euc
 
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Great news. Glad it all went well. Any chance of uploading the footage of the drone falling. Will make great viewing

Neon Euc

Sorry, no footage. The cam stopped recording spontaniuosly 30 seconds into the flight. Believe me, I would have liked to have seen it too.
 
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Do not believe these guys about "Active braking" . There is a popular misconception here on these forums that the drone somehow stops or reverses or almost stops the propellars to slow down, when it actually simply tilts opposite of the direction it is going and applies MORE prop speed. Think about it. The drone moves by tilting one direction or the other. Slowing or stopping the props would get you NOTHING. It is not like reversing your prop on a boat to slow down/stop or the variable pitch prop on an aircraft engine.
Do you believe DJI? From their own tuned propulsion system literature "Active braking: The motor will provide reverse torque actively to slow down the propeller, and the rotational energy will be recovered". This suggests the motor is switched to act as a generator during commanded deceleration events (presumably the output is rectified and returned to the battery terminals). A similar system is employed on the spindle drives of my CNC routing machines where a resistor bank is employed instead of a battery.

This is not a forum perpetuated myth- the current motors do decelerate much quicker than standard BLDC systems and will spin off improperly installed propellers.
 
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