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Motor Failure Or Something Else?
2745 36 2018-7-11
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sam.yoursiteteam
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So im trying to figure out just WTF happened.

Over the weekend, mid flight, without warning the drone seemed to get erratic and then just flipped over and then proceeded to drop 300 feet and crash. The fall was cushioned by some trees and the structure is relatively unharmed.. in fact, I didn't even break a propellar. It was a clear day, I was in the open, the breeze was light and nothing abnormal happened before or during the flight. I'm just baffled.

Once I recovered it, I had 2 errors reporting. Something about motor speed exceeded and board error.  I don't know if those errors were caused by the crash or are the cause of the crash. I had no warning or alerts before the crash so its leading me to believe that those errors were caused after the failure.

Overall, I am just trying to wrap my head around what went wrong, what I could have done to avoid it and what to do to prevent it from happening again

Was it a motor failure or something else? Any insight would be appreciated

This is the short version just before and during the crash.



This is the entire flight.




2018-7-11
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Mark The Droner
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If you post the log, we might get a hint...

http://www.phantomhelp.com/LogViewer/Upload/
2018-7-11
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sam.yoursiteteam
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Just pulled the logs but the info said it was last updated in 2017 which does not seem right

Anyhow, this is what I got, but I dont think its correct.
http://www.phantomhelp.com/logviewer/PDMGL6U2KOG6KWET5L3K/
2018-7-11
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sam.yoursiteteam
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sam.yoursiteteam Posted at 2018-7-11 13:37
Just pulled the logs but the info said it was last updated in 2017 which does not seem right

Anyhow, this is what I got, but I dont think its correct.

disregard this, im a DOLT.. I pulled this off of my ipad and I was using my phone in this case.  Im pulling the log now
2018-7-11
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Ray_Drone_Pilot
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This is really sad and my biggest worry ever happens to my bird. I hope you can find out what has happend, I'm really curious about it. Anyhow your really lucky not a lot of damaged occured during this fall from 300ft
2018-7-11
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sam.yoursiteteam
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OK here is the correct log

http://www.phantomhelp.com/LogViewer/PDKXM6SJKODNKVC96L11/
2018-7-11
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Mark The Droner
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So you found the AC with all four props intact, undamaged, and still tightly screwed onto the motors?  Right?  
2018-7-11
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sam.yoursiteteam
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yep, everything was still tight, attached connected and the power was still on.
2018-7-11
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sam.yoursiteteam
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The camera is fine, the gimble is fine.  It powers up and connects and everything seems to function fine, except for the fact it wont start now.
2018-7-11
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ALABAMA
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Looks like your battery crapped out on ya. How old is it?
2018-7-11
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sam.yoursiteteam
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2 years in September.  The batteries are not that old though.  Maybe a little over a year or so.
2018-7-11
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Mark The Droner
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I'm gonna take a wild guess that something is wrong with your flight controller, also known as your master controller.  I think you were getting false readings re altitude before the crash started and this continued and led to the crash.  Your IMU might have gone bad which led to it going crazy.  That's my uneducated humble opinion.  And I agree with Alabama that something might be up with your battery but I don't see how that caused your crash.  Maybe somebody else can come up with something better.  Good luck.
2018-7-11
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ALABAMA
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Labroides will be along to properly read your log.  He can tell for sure what exactly happened.
2018-7-11
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Labroides
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At 1:55.2 things come unstuck.
You were hovering and the Phantom lifted its nose/dropped its tail end and then rolled sideways.
You had hands off the joysticks at the time.
The battery was healthy at the time.
Data recording continued as the Phantom fell
It looks like a hardware fault and nothing you could have done to prevent and nothing you could do to recover.
The false altitude + speed readings are all after the impact with the tree and are due to the IMU sensors getting a big knock.

2018-7-11
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Mark The Droner
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Labroides Posted at 2018-7-11 20:02
The false altitude + speed readings are all after the impact with the tree and are due to the IMU sensors getting a big knock.

According to the log, the first speed error was when he was happily flying at 90 feet altitude.  The log shows he jumped up 20 feet in altitude in about a second and a half while enduring speed errors and then inverted and started the violent descent with speed errors all the way down...
2018-7-12
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Bashy
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The interesting part in this is that he said he was flying at 300ft...........
2018-7-12
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Ray_Drone_Pilot
Second Officer
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How does one  prevent such terrible things happen? Or is it normal that after 2 years flying your drone the machine fails for some kind of reason and fall out of the sky? Imagine it drops on someones property or worse someones head or so.
2018-7-12
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Mark The Droner
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Bashy Posted at 2018-7-12 04:16
The interesting part in this is that he said he was flying at 300ft...........

He said it dropped 300 feet.  If you look at the terrain, you can see it goes downhill towards the lake which is the direction he flew
2018-7-12
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Mark The Droner
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Ray_Drone_Pilot Posted at 2018-7-12 04:27
How does one  prevent such terrible things happen? Or is it normal that after 2 years flying your drone the machine fails for some kind of reason and fall out of the sky? Imagine it drops on someones property or worse someones head or so.

I think it is normal, yes.  I don't think you can put a timeline on it but something is going to go wrong eventually unless you retire it and buy a new one.  But it shouldn't drop on top of somebody's head because we follow the rules.  :-D  
2018-7-12
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odontologo98
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1m 57.4s        battery 89%           13.809V        3.369V        3.437V        3.486V        3.517V

usually 3.5v = 0mah remaining

apparently bad battery.

Defective batteries drop the voltage very quickly.
2018-7-12
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odontologo98
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How many times has your battery been recharged?

2018-7-12
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Landbo
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odontologo98 Posted at 2018-7-12 05:55
1m 57.4s        battery 89%           13.809V        3.369V        3.437V        3.486V        3.517V

usually 3.5v = 0mah remaining

The first statement is fairly accurate. But the low voltage is due to something in the quad that has drawn a lot of power. Here is a transistor in one of the engines ESC the near only option provided it is not a short circuit in a motor. You can look out of the log that the voltage rises again when the controller turns off the engines.

Will guess that the machine smells of burned electronics when it is opened.

Regards, Leif
2018-7-12
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sam.yoursiteteam
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Mark The Droner Posted at 2018-7-12 05:02
He said it dropped 300 feet.  If you look at the terrain, you can see it goes downhill towards the lake which is the direction he flew

I started on top of a ski slope.  As I went strait out the altitude increased due to the downward slope of the hill thus it was not recorded as an altitude increase.  

I basically flew strait out.  By the time I was at the end of the ski slop, I was several hundred feet high.  Im estimating that it was 300ft, but I could be grossly wrong.
2018-7-12
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sam.yoursiteteam
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odontologo98 Posted at 2018-7-12 06:23
How many times has your battery been recharged?

Im not sure of an exact number, but it has not been an inordinate amount.  They hold a charge well and usually last 20ish or so minutes depending on conditions.
2018-7-12
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sam.yoursiteteam
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Landbo Posted at 2018-7-12 06:42
The first statement is fairly accurate. But the low voltage is due to something in the quad that has drawn a lot of power. Here is a transistor in one of the engines ESC the near only option provided it is not a short circuit in a motor. You can look out of the log that the voltage rises again when the controller turns off the engines.

Will guess that the machine smells of burned electronics when it is opened.

Even after the crash, everything still works with the exception of being able to start.  Camera connections is great, lights are perfect.. everything seems perfect except for the obvious lack of motors starting
2018-7-12
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sam.yoursiteteam
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Does anyone have any experience with DJI repair services?  Do they offer discounted/free repairs for catastrophic equipment malfunctions?
2018-7-12
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ALABAMA
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sam.yoursiteteam Posted at 2018-7-12 08:09
Does anyone have any experience with DJI repair services?  Do they offer discounted/free repairs for catastrophic equipment malfunctions?

Only if it's still under warranty, and if something was defective.
2018-7-12
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Landbo
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sam.yoursiteteam Posted at 2018-7-12 08:08
Even after the crash, everything still works with the exception of being able to start.  Camera connections is great, lights are perfect.. everything seems perfect except for the obvious lack of motors starting

An error message should appear when you try to start the engines. Do you not see anyone in DJIGO3 ?

Regards Leif.
2018-7-12
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Ray_Drone_Pilot
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Mark The Droner Posted at 2018-7-12 05:05
I think it is normal, yes.  Something is going to go wrong eventually unless you retire it and buy a new one.  But it shouldn't drop on top of somebody's head because we follow the rules.  :-D

Hmmm so eventually my birds will fall out of the sky one day. Thats still a bit weird IMHO if you buy a card or bycicle you don't buy it with the knoweledge it willl give you a crash one day. As long you take good care of the equipement. I dont want to be annoying please don't get me wrong. But it would be nice there would be some feature that tells you maintance is acquired.

But it is as it is so I will have to accept that.

Yes youre true about the rules so it should not drop on someones head true.
2018-7-12
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sam.yoursiteteam
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Its boxed up and being shipped out tomorrow for them to evaluate.

It would be nice if there were a prescribed maintenance plan like a car has.  Change motors after "x" amount of useage/time as well as some other diagnostic health software that would tell you if there is a high percentage of failure after a certain amount of time... Kind of like that WATSON commercial, on TV, that recommends part replacements on the airplane after a set time.  

Its probably overkill, but it was a like a punch in the gut watching my bird drop so far, so fast for no apparent reason... UGH!
2018-7-12
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Mark The Droner
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Please be sure to come back and tell us what the story is
2018-7-13
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endotherm
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I don't think it has anything to do with the battery.  These are 15.2V batteries which won't start issuing warnings until about 3.3V per cell.  They will need to get down to 3.0V per cell before they shut the battery down to protect it.   I agree that there was probably an internal hardware fault that was drawing a lot of power, for example a failing IMU or a dry solder joint.  We have previously seen a case of a heavy wire from the main board to the motor cracking, probably due to a crash or hard landing or maybe just fatigue, which caused a similar fall and crash.  Even if inspected for maintenance this fault was not likely to be detected as the crack was inside the plastic sheath and not visible.  It is possible in this case there was a similar crack and it arced causing high current consumption, eventually leading to a complete separation and failure.  If you are not sending it in, I'd be checking these wires first.  A disconnected wire would explain why it is the only component not wanting to start up again.

The battery clearly did not shut down, as it was still recording the fall and sending telemetry all the time.  We see the capacity rebound once the load is removed.  The front two props at least were spinning the whole time during the fall, as seen on the video.  One or both of the rear props must have stopped.  I suspect the right-rear due to the way it tumbled initially.  This can only be checked if the DAT file contained on the aircraft's internal "black box" recorder is extracted and examined, or if a physical examination of the electronics is performed.

For safety most countries forbid flying over people.  This is in anticipation of the unexpected happening and it falling on them.  It is impossible to develop a maintenance regime that will forsee any disaster, so you need to anticipate S**T HAPPENING and fly accordingly to minimise collateral damage.

All the crazy readings at the end of the log are as a result of the failure, not the cause of it.


Battery voltage per cell:
batt V per cell.png

Battery voltage
and remaining capacity:
batt volt & pct remain.png

Temperature
vs capacity:
batt tmp vs consumption.png
2018-7-14
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sam.yoursiteteam
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So here is an update.  I sent the unit back to them along with the description on what happened,  videos, the data file and a bunch of questions as to what happened and why.  They did not answer any of my questions and only responded that that there was moderate to severe body damage.  They said they would replace or repair the faulty items.  

A few days after thatI receive a payment request for $88 which I thought was fair. I paid it and a week later (today) I received, what appears to be, a brand new/refurb unit. Everything looks brand new and all of the serial numbers are different than my prior one.  I have not had a chance to put it up in the air yet, but I have little doubt that it will be fine.

So... I'm VERY happy that they replaced it for $88 even though its warranty has been expired for well over a year. I would like to have known their thoughts on what caused the failure though.  All in all, I have to say that I am happy with the service (pending the initial flight).

THANK YOU ALL for your insight and data analysis. Its great to be part of a community of such helpful nerds...AND by NERD, I mean the most intelligent and insightful group of enthusiasts... I am very grateful for the help & direction!
2018-9-18
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sam.yoursiteteam
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endotherm Posted at 2018-7-14 16:43
I don't think it has anything to do with the battery.  These are 15.2V batteries which won't start issuing warnings until about 3.3V per cell.  They will need to get down to 3.0V per cell before they shut the battery down to protect it.   I agree that there was probably an internal hardware fault that was drawing a lot of power, for example a failing IMU or a dry solder joint.  We have previously seen a case of a heavy wire from the main board to the motor cracking, probably due to a crash or hard landing or maybe just fatigue, which caused a similar fall and crash.  Even if inspected for maintenance this fault was not likely to be detected as the crack was inside the plastic sheath and not visible.  It is possible in this case there was a similar crack and it arced causing high current consumption, eventually leading to a complete separation and failure.  If you are not sending it in, I'd be checking these wires first.  A disconnected wire would explain why it is the only component not wanting to start up again.

The battery clearly did not shut down, as it was still recording the fall and sending telemetry all the time.  We see the capacity rebound once the load is removed.  The front two props at least were spinning the whole time during the fall, as seen on the video.  One or both of the rear props must have stopped.  I suspect the right-rear due to the way it tumbled initially.  This can only be checked if the DAT file contained on the aircraft's internal "black box" recorder is extracted and examined, or if a physical examination of the electronics is performed.

Thanks for the detailed analysis!  That was very helpful and insightful!  The amount of data that is available for analysis I quite impressive and I find it fascinating!
2018-9-18
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ALABAMA
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Glad you got it replaced.
2018-9-18
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Sayhelloforme
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sam.yoursiteteam Posted at 2018-9-18 08:16
So here is an update.  I sent the unit back to them along with the description on what happened,  videos, the data file and a bunch of questions as to what happened and why.  They did not answer any of my questions and only responded that that there was moderate to severe body damage.  They said they would replace or repair the faulty items.  

A few days after thatI receive a payment request for $88 which I thought was fair. I paid it and a week later (today) I received, what appears to be, a brand new/refurb unit. Everything looks brand new and all of the serial numbers are different than my prior one.  I have not had a chance to put it up in the air yet, but I have little doubt that it will be fine.

I’m happy they replaced it. Let us know how the new one flys.
2018-9-18
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Siambuddhas Group
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That's what I mentioned before,they should come up with an application to diagnose and store motors lifespans and spins.circuit board current defective check and chipset...maybe in my dream.
2018-9-19
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