Mavic Pro Platinum strange crash

[orion900]

Hello, my first post in the forum, I have created same thread in DJI official forum last week, but I guess might be more answers and ideas here.

I have (had) Mavic Pro Platinum drone, which I bought second hand, but it's almost new, currently have only ~10 cycles on all 3 batteries.
Last Saturday I took it to country-side, wanted to refresh my flight skills after the winter flew around little bit, brought it up to 500 meters, went 1km away from house, then I was flying it back, something happened, drone started to spin around and fall down, lost the connection and I started to run to it's last map location, was sure it has crashed. Several seconds later heard the noise, drone was coming back home, but spinning around really fast, like helicopter without it's tail rotor. Positioned itself to launch location and just fell from 40 meters in free-fall. was 1 propeller broken off completely, but forgot which leg. (by the way propellers were completely new)
I have extracted TXT log from the phone - DJI Flight Log Viewer - PhantomHelp.com
Later extracted DAT file too - http://www.improvizus.lt/22-03-19-06-04-50_FLY023.DAT

At 7min 21s. it seen that right rear motor dropped it's RPM from 7000 to 66, motor obstructed error occurred. At first I was unable to view video, as the format was unreadable, but a week later was able to fix the video file, and was surprised it really crashed into the trees and looks like impact made rear right motor to start spinning again, return to home engaged, and looks like one propeller blade was missing, that's why it was spinning on the way home. Video of crash -

Any ideas what might happened at first?

 

[slup]

It's very clear why the drone start to rotate & lose height at 438,6sec into the flight ... the rear right motor stops rotating & doesn't generate any thrust.

The root cause isn't as simple as a blocked motor or a failing prop though...

If looking at the moment where the main incident starts, at 438,6sec into the flight and check how the problematic motor is behaving where the drone rotation/tumbling starts.

-The green graph is the yaw movement on a 360 degree axis
-The black graph is the motor rpm
-The blue graph is the Flight controllers command percentage for the motor
-And the dashed purple is the rudder stick command

Clearly the flight controller doesn't get what it requires, the rpm falls quickly to near 0rpm's while the FC want's between 92-97% of full rpm. This makes the drone to start rotate due to the torque imbalance & lose height faster then before.

(Click on the chart's below to make them larger)


At 462,5sec the rear right motor start to rev up again, but there the drone is down at 15m above the HP & have probably damaged a prop blade against those trees seen in the video clip ... the damage isn't worse than it can produce enough thrust for gaining height ... but it can't stop the rotation due to still having a thrust generated torque imbalance.



In the end at 634,7sec, there up on approx 40m height all motors turn off & the drone free falls to the ground.



Looking again at the first initial incident we see that this doesn't fully look like a blocked motor ... usually that means that the motor current sky rockets ... but that doesn't happen here, even though the motor doesn't move & the FC wants nearly max revs.

The dashed yellow graph is the rear right current draw ...



If looking into the DAT log event stream we see that the problems started off much earlier than when the main incident started ...

Already at 240,3sec into the flight the errors start to build up regarding propulsion troubles ...


When the main incident starts this is seen ...


And when the motor start to work again ...


So the root cause for this whole incident is most probably electrical ... affecting the ESC for the rear right.

That the drone shuts off all motors in the end is due to the wild tumbling which turns the drone upside down ...

 

[RayOZ]

A valiant effort from the little guy trying to get home with 3 props. Even got back up after almost crashing to the ground the first time. Battled the tree branches to get back up in the air. Would make a great movie.

 

[eEridani]

The video is very clear the left front prop had issues during a nice slow descending turn; then things went south. 3:06 in the video. What happens to the motors after the impact with trees is a don't care. The important event was early in the flight just before the spin.

 

[slup]

The video is very clear the left front prop had issues during a nice slow descending turn; then things went south. 3:06...

Read the full analysis in post #3 ... nothing happened to any of the drones props during that descending turn, the left front prop was equally unaffected as the other 3.

At 438,6sec into the flight (approx. 3:06min in the video) ESC 4 stalls making the rear right motor stop.

 

[orion900]

Read the full analysis in post #3 ... nothing happened to any of the drones props during that descending turn, the left front prop was equally unaffected as the other 3.

At 438,6sec into the flight (approx. 3:06min in the video) ESC 4 stalls making the rear right motor stop.

Hello, first of all, want to thank you very much for such professional crash analysis and your help. I have shipped the drone for repairs, technician replaced following parts (with new, original DJI replacement parts):

• top housing
• middle housing
• front right leg with motor
• back right leg with motor
• camera cables

But since you mentioned this most likely been electrical problem, now I am afraid to fly the fixed device, may I ask do you think the electrical problem was in right back motor ESC? As I understand it's located under the motor, so now replaced with new part, or the problem might have been in mainboard (which is same as the crash happened)?

Also why do such electrical problems might happen, is it manufacture problem (unnoticed DJI spoilage) or I might done something to make this happen, like improper storage, hard flying (always full stick) on sports mode etc.?

PS. attaching image of fixed device

 

[slup]

Hello, first of all, want to thank you very much for such professional crash analysis and your help. I have shipped the drone for repairs, technician replaced following parts (with new, original DJI replacement parts):

• top housing
• middle housing
• front right leg with motor
• back right leg with motor
• camera cables

But since you mentioned this most likely been electrical problem, now I am afraid to fly the fixed device, may I ask do you think the electrical problem was in right back motor ESC? As I understand it's located under the motor, so now replaced with new part, or the problem might have been in mainboard (which is same as the crash happened)?

Also why do such electrical problems might happen, is it manufacture problem (unnoticed DJI spoilage) or I might done something to make this happen, like improper storage, hard flying (always full stick) on sports mode etc.?

PS. attaching image of fixed device
View attachment 145947

The log clearly points out that ESC (4) have stopped working ... & by that the right rear motor stops. The reason for the ESC stall isn't clear, but as the ESC later resumes it's function (& the motor starts to rotate again) ... the ESC hadn't been burned out, something before the ESC is likely the true cause.

As the drone is man made nothing with it will ever be 100% fail safe, electronics fail, hardware fail, software fail ... sometimes due to how they are used/stored, or due to manufacturing flaws ... no one can predict when a electronic device will fail by just looking at it. But as electronics usually are sensitive to current & heat ... going hard in Sport mode during longer periods in hot ambients will for sure put extra strain on the electronic components.

The only thing you as a pilot can do is to expect the worst & hope for the best ... meaning don't fly over/near objects/people you don't want to damage/cause injury too & keep the flights within the drone regulations.

 

[Yaros]

now I am afraid to fly the fixed device

I suggest you fly the drone, but don't fly to 500 meters and don't go far away or fly in Sport Mode. I would keep the drone below 30 meters on the first flight.

 

[Capt KO]

Very interesting, thanks for posting. One of the best crash videos I’ve seen. Glad you were filming. Hope all ok now.

 

[eEridani]

Hello, first of all, want to thank you very much for such professional crash analysis and your help. I have shipped the drone for repairs, technician replaced following parts (with new, original DJI replacement parts):

• top housing
• middle housing
• front right leg with motor
• back right leg with motor
• camera cables

But since you mentioned this most likely been electrical problem, now I am afraid to fly the fixed device, may I ask do you think the electrical problem was in right back motor ESC? As I understand it's located under the motor, so now replaced with new part, or the problem might have been in mainboard (which is same as the crash happened)?

Also why do such electrical problems might happen, is it manufacture problem (unnoticed DJI spoilage) or I might done something to make this happen, like improper storage, hard flying (always full stick) on sports mode etc.?

PS. attaching image of fixed device
View attachment 145947

Despite @slup 's opinion, pretty sure prop flex on that last acceleration caused one of the props to fail. You can see the front prop flexing in the video at 3:06, and undoubtedly the rear props were flexing just as much. Once a prop breaks, pieces can fly into the motors but this means 0 rpm which isn't in the log. But with a simple broken prop the logs will show overspeeds as the motor spins up with 1/2 the load, vibrations, and depending on firmware the drone may even shut down a motor.

I'm not buying the electrical problem theory.

 

[Capt KO]

Were the props possibly aftermarket? You said they were new. Wouldn’t stop a motor though, the main cause from the logs.

 

[slup]

Despite @slup 's opinion...

Sorry, but that' s not a opinion... it's facts straight out from the DAT log.

But yeah... I know that you earlier have claimed that log data can be false & can't match your opinions.

 

[eEridani]

Sorry, but that' s not a opinion... it's facts straight out from the DAT log.

But yeah... I know that you earlier have claimed that log data can be false & can't match your opinions.

It is your opinion @slup - the log says the motor stalled, not the ESC. After the stall, which was very likely prop damage, the ESC turned OFF the motor. That is what the log says. Yet you make the claim it's an electrical issue. And that claim (copied below) is your OPINION based on your interpretation of log data.

So the root cause for this whole incident is most probably electrical ... affecting the ESC for the rear right.

My interpretation of the log data is different than yours because most failures have a cause and effect, and the ESC was operating normally the entire log duration; however the motor was not responding to the power applied. This may be supported by the fact the drone was fixed with no electronics replacements and the ESC is working.

 

[orion900]

It is your opinion @slup - the log says the motor stalled, not the ESC. After the stall, which was very likely prop damage, the ESC turned OFF the motor. That is what the log says. Yet you make the claim it's an electrical issue. And that claim (copied below) is your OPINION based on your interpretation of log data.



My interpretation of the log data is different than yours because most failures have a cause and effect, and the ESC was operating normally the entire log duration; however the motor was not responding to the power applied. This may be supported by the fact the drone was fixed with no electronics replacements and the ESC is working.

Hey, thanks for your post, as I understand the original leg replacement comes together with motor and ESC.

Anyhow, I would like to add, that props were new, but they were bought from aliexpress, I am never putting aftermarket props again, now have original kit. after the crash, one blade was broken, other one was missing together with metal holder pin. I have marked how propeller looked like after crash.

Would it be possible that prop holder pin partially broke, and after one blade dislodged making motor hard to spin and reducing rpm to almost none, and then hit to the tree branches made it loose partially broken propeller and comming home without one blade?

 

[slup]

It is your opinion...

It's clear that you can't distinguish between an opinion & a analysis ...

If you do an analysis ... "you break all available data down into its various elements and then asking critical thinking questions such as WHY and HOW in order to reach some conclusion"

If you have an opinion ... "you form a view or judgement about something, not necessarily based on facts or knowledge"

Below is your opinion ... which either not taking facts into consideration, or plainly contradicting the data from the logs ...

The video is very clear the left front prop had issues... What happens to the motors after the impact with trees is a don't care.

You seems to use ... (or at least that's the only data you refer to & present) the video as the main source, not a single pointer to anything from either the attached TXT or DAT log.

If you had looked into the telemetry data you had seen that nothing there supports any kind of failure in the Left Front side ...

If a craft rapidly rolls to the right together with pitching up ... that can't possibly mean Left Front problems, if you also add in the motor data from the DAT log to this with a Rear Right motor that stops ... your opinion becomes even harder to understand.

...My interpretation of the log data is different than yours because most failures have a cause and effect, and the ESC was operating normally the entire log duration...

Well ... then you just fail to see the whole picture.

Why does this show up in the DAT log event stream long before the main incident starts..?


And you say that the ESC was operating normally..?


And why the stopped motor starts to spin again doesn't interest you..?


And you doesn't bother to answer the OP's question why the MPP free falls in the end..?


Furthermore...

If using common knowledge combined with data from the DAT log shows that this doesn't show the common characteristics of a blocked motor ... if a motor gets blocked it's been shown in countless incidents that the motor current draw from the blocked motor easily will be the highest ... we don't see that here, how come?

 

[slup]

...Would it be possible that prop holder pin partially broke, and after one blade dislodged making motor hard to spin and reducing rpm to almost none...

That's not how it works ...

If a prop blade breaks off the drag will decrease ... making that motor rotate with less counter force, it will spin easier. And due to the lost blade that prop produce less thrust making the flight controller command the motor to rotate faster to regain the lost thrust.

So the consequence is the opposite ... with a lost prop blade the motor will rotate easier & faster.

 

[BudWalker]

The video is very clear the left front prop had issues during a nice slow descending turn; then things went south. 3:06 in the video. What happens to the motors after the impact with trees is a don't care. The important event was early in the flight just before the spin.

The object seen in the upper left corner of the video isn't the left front prop. Instead, it's the MP itself. When the MP rolls CCW and pitches down the gimbal will pitch up in response. Here's a video I did with my MP.

The MP was held level and then rolled CCW and pitched down

 

[BudWalker]

@orion900 I agree with @slup. The problem is most likely related to the ESC not a broken prop. If you want further evidence this is the case you'll need to provide the .DAT from the MP itself. The Motor:V_out signal shows the voltage that the ESC outputs. Normally it tracks the MotorWM signal; i.e. the FC command to the motor. For some reason this field is 0.0 in the .DAT you provided. The on board .DAT generally has better data and may have valid Motor:V_out data. But, if it is also shows Motor:V_out being 0.0 that would indicate some problem in the ESC sensor circuitry.

For instructions on retrieving the on board .DAT go here
How to retrieve a V3 .DAT File from the AC

 

[slozukimc]

Sorry, but that' s not a opinion... it's facts straight out from the DAT log.

But yeah... I know that you earlier have claimed that log data can be false & can't match your opinions.

Ok. I have to say something as a mechanic for over 30 years. Sometimes the data logs aren’t incorrect but there is a mechanical reason that makes it seem they could be to the untrained eye. The combination of data and inspection need to be used together.

The reason the front left prop is coming into view to a mechanics eye would be loss of thrust on the right rear so that supports the data as well.

Now, why? Has the drone been used in sandy areas?

I believe @Phantomrain.org had a prop failure that blocked a motor on his M3? Could this be a similar thing?

Remote possibility but could a small bird have come in contact with the rear motor and become lodged between the prop and drone for a bit?

Lots of mechanical and/or electrical things it could be but just because the daya does not match and opinion surely doesn’t mean it is wrong.

Mike

 

[slup]

...Sometimes the data logs aren’t incorrect...

I guess you were going to say ... "aren't correct"?

Have never, during several years of incident investigation, seen a log with either telemetry or sensor data that are just "a bit" wrong ... like showing roll to the left instead of right. When data in the logs deviate from reality, it's off by a huge amount ... like in a recent case where the reported height suddenly said negative height with several hundred meters when the flight was conducted on a parking lot.

It's rarely any doubt if the data is reliable or not.

...The combination of data and inspection need to be used together.

That's all good, but usually a luxury when it comes to a drone that have fallen to ground from 500m height, especially if you don't have the corpse on hand. The logs contain several hundreds of data signals & many of them can be put up against each other in order to determine which is likely & can be trusted. If we, as in this case also have a video capturing the incident ... that of course goes in as one piece of the puzzle & the total analysis.

Already in post #15 I explained what a analysis is ... "you break all available data down into its various elements and then asking critical thinking questions such as WHY and HOW in order to reach some conclusion"

The reason the front left prop is coming into view...

If you look at post #17 you can see a simulation done with a MP moving according to the recorded telemetry ... It's not the prop you see in the video clip from the OP ... it's likely the fuselage.

... a prop failure that blocked a motor..? Remote possibility but could a small bird have come in contact with the rear motor and become lodged between the prop and drone for a bit?

Without going into what thing's that can block a motor ... a blocked motor always have a certain characteristic influence on the recorded log data. If something by force blocks a electrical motor that is commanded to turn with maximum rpm's that will create a very clear & high amp draw from that motor. This burns the motor eventually as the energy put in doesn't generate rotation ... it instead generate heat in the motor coils.

So if we can't see this amp increase for the stopped motor ... it usually means that the cause isn't anything mechanically blocking the motor, the cause is something else.

And if we there also see log information about ESC failures ... the cause is rather electrical than mechanical.

Lots of mechanical and/or electrical things it could be but just because the daya does not match and opinion surely doesn’t mean it is wrong.

I'm fully aware of that ... that's why I & several others make analyzes, we don't just throw out opinions as soon as we see a shadow coming into the video frame ... & immediately draw conclusions that's not supported by other data also on hand.

Opinions is actually rarely relevant when it comes to incident analysis ... this as opinions tends to be "you form a view or judgement about something, not necessarily based on facts or knowledge"

Ideas on the other hand ... that needs to be investigated further & either proven or discarded ... yes, all analysis activity start with that.