Hi, after more than 200 flight it fell

[Bojan]

After almost two years, 140km, 20hours of flight, it fell.
I was flying over sea and hidden myself under the tree since its impossible to see phone screen with high sun.
My drone was directly above me, but high. I dont know what happened but I suggested some bird punched or something.
From log flight is that the motor is blocked.
One of the theories I have is that the bird punched one of the back legs so the leg flipped itself under drone, like when you put it in a storage box.
But If any one can just confirm that or anything else. Thank you.
And hoped that I managed to share flight log from AirData.

 

[slup]

...it fell.
...I dont know what happened but I suggested some bird punched one of the back legs so the leg flipped itself under drone, like when you put it in a storage box.

That theory is far fetched & nothing in the log supports that.

Instead you lost the thrust due to either a prop or a motor failure ... most probably in the rear right corner if going through the AC movements in Pitch, Roll & Yaw.

As seen here below in the chart, you came in with full speed in Sport mode, dropped the elevator stick (right stick forward/backward) to neutral & instead started to apply full throttle down (left stick forward/backward) together with some left rudder input (left stick left/right). Slightly after that the AC had started to break it shortly pitched nose up, back down & rolled over to the right ... at the same time the motor blocked message turned up (light blue background color in the chart) and the AC started to rotate CW ... as the rear right side, which most probably were lost, is CCW torquing it was an over weight to rotate the AC CW (2 sides torquing CW + only one functional side CCW torquing).

The dotted lines in the chart is your stick inputs ... see the legend below the chart for what the graphs means. The marker in the chart is where the incident happens.

(Click on the chart to make it larger)


If you retrieve the corresponding mobile device .DAT log for this flight we should be able to see if it was a prop or a motor that failed. The correct .DAT log ends with FLY072.DAT. Read up here on how to retrieve --> Mavic Flight Log Retrieval and Analysis Guide (read under point 3.) Once retrieved attach it in a new post here.

 

[Bojan]

First of all. Thank you.
I am little curious about this crash. Because it is possible that birds had to do something with drone. But I am little familiar with drone and birds and I dont think it is possible that day STUCK motor. No evidence of birds was found on drone.
As it felt, I am unable to tell is it because it felt or why, but both left motors front and back are unable to rotate. Motors are completely stuck.
Regarding flight record, MCDatFlightRecords is empty. I managed to find only .txt and .log files. And I cant guarante the files are DJI whatsoever. -D)
fly072.dat is non existing on phone.
And fc_log.log is retrived from sd card.
As I see I will have to uninstall apps and so on to find .dat?
And thank you once again.

 

[Bojan]

fc_log.rar

drive.google.com

I think this is fc_log.log, in rar

 

[slup]

...I think this is fc_log.log

Ok ... if the mobile device DAT log FLY072.DAT is gone (which they usually are as they gets deleted once a sync to the DJI servers are made) ... the SD card fc_log.log will do.

The commands you made there just before the incident starts ... first full speed forward, then full break + full descent during the breaking + input for yaw with the rudder stick make it hard to interpret just from the AC movements, exactly which side that gives up & don't provide enough thrust ... so it's not the rear right side that causes this, instead the other CCW torquing side ... the front left.

This was the stick inputs you made alone, at 561,1sec you releases all sticks to neutral, but approx. a second later you at the same time apply 3 different stick inputs, rudder (yaw, CCW rotation), throttle (for descend) & a blip of elevator (for forward speed) ...


If we look at the RPM's for the 4 motor sides around 562,2sec, marked below... just when you get the message about "Motor Blocked". We see that just before that when you return all stick to neutral, the RPM's for all 4 motors rapidly decrease at first (most in the left front, blue graph). Then moments later after 562,2sec, 3 motors decrease their RPM even further (but not to the low level of the left front) ... this as a result of you starting to apply throttle inputs for descend. As you return the throttle stick to neutral again & momentarily stop the descent, 3 of the four motors increase the RPM again but not the left front ... & it's here you get the "Motor Blocked" message.



If we in relation to the motor RPM's in above chart check off how the flight controller actually wanted them to operate ... below you have the percentage of available RPM that is commanded by the FC. The blue graph that represent the left front motor goes to a 100% command at 562,4sec ... but as seen in the chart above the RPM (blue graph) doesn't increase at all.



So ... the left front motor doesn't obey the FC command to rev up the RPM from approx. 561.9sec. This could mean that it have got blocked either by a seized bearing or some debris.

To confirm the "blocked motor" theory further we can look at the current draw for the motors ... if a motor is stuck & can't rotate but is commanded to increase the RPM the current draw usually increases. And that is what we see in below chart where the left front (blue graph) spikes up higher than the other 3 motors.

In the end this shows that no bird was involved at all ... instead the front left motor got jammed for some reason & that caused it to quickly come tumbling & rotating down.



Here the sequence of events in a sat picture... The start of the painted black arrow is the left side of all charts shown above. The left front motor gets blocked at the red cross ... which induce a rotational torque unbalance which make the AC tumble & spin down along the dotted black painted arrow.

 

[Bojan]

Slurp, dont know how to thank you. You should be doctor or in NASA reading some charts. :-D
Thank you very very much.
I dont know why but I just wanted to confirm to myself that it wasnt birds.
Dont know why motors stuck. But even now front left motor is unable to rotate. Although it doesn't show any signs of crash or anything at all. Not even a scratch. The only thing that is visible is some silver like really small metal piece inside rotors. Dont know is this blocking. Or did it show after fall.

 

[slup]

...front left motor is unable to rotate. Although it doesn't show any signs of crash or anything at all. Not even a scratch. The only thing that is visible is some silver like really small metal piece inside rotors...

It's always hard to find the root cause for a motor that gets blocked airborne ... then falls spinning into the ground from 159m height.

The shavings inside the motor could indicate that some debris was inside the motor ( a grain of sand?) and shaved off some metal when slowing down the motor (your motor wasn't totally stopped, it had approx 1600rpm until the log ends)

 

[DavidT_ NZ]

Ok ... if the mobile device DAT log FLY072.DAT is gone (which they usually are as they gets deleted once a sync to the DJI servers are made) ... the SD card fc_log.log will do.

The commands you made there just before the incident starts ... first full speed forward, then full break + full descent during the breaking + input for yaw with the rudder stick make it hard to interpret just from the AC movements, exactly which side that gives up & don't provide enough thrust ... so it's not the rear right side that causes this, instead the other CCW torquing side ... the front left.

This was the stick inputs you made alone, at 561,1sec you releases all sticks to neutral, but approx. a second later you at the same time apply 3 different stick inputs, rudder (yaw, CCW rotation), throttle (for descend) & a blip of elevator (for forward speed) ...
View attachment 133620

If we look at the RPM's for the 4 motor sides around 562,2sec, marked below... just when you get the message about "Motor Blocked". We see that just before that when you return all stick to neutral, the RPM's for all 4 motors rapidly decrease at first (most in the left front, blue graph). Then moments later after 562,2sec, 3 motors decrease their RPM even further (but not to the low level of the left front) ... this as a result of you starting to apply throttle inputs for descend. As you return the throttle stick to neutral again & momentarily stop the descent, 3 of the four motors increase the RPM again but not the left front ... & it's here you get the "Motor Blocked" message.

View attachment 133621

If we in relation to the motor RPM's in above chart check off how the flight controller actually wanted them to operate ... below you have the percentage of available RPM that is commanded by the FC. The blue graph that represent the left front motor goes to a 100% command at 562,4sec ... but as seen in the chart above the RPM (blue graph) doesn't increase at all.

View attachment 133622

So ... the left front motor doesn't obey the FC command to rev up the RPM from approx. 561.9sec. This could mean that it have got blocked either by a seized bearing or some debris.

To confirm the "blocked motor" theory further we can look at the current draw for the motors ... if a motor is stuck & can't rotate but is commanded to increase the RPM the current draw usually increases. And that is what we see in below chart where the left front (blue graph) spikes up higher than the other 3 motors.

In the end this shows that no bird was involved at all ... instead the front left motor got jammed for some reason & that caused it to quickly come tumbling & rotating down.

View attachment 133623

Here the sequence of events in a sat picture... The start of the painted black arrow is the left side of all charts shown above. The left front motor gets blocked at the red cross ... which induce a rotational torque unbalance which make the AC tumble & spin down along the dotted black painted arrow.

View attachment 133624

I’m sure I’m not alone in saying that the information that you (and others) have gleaned off this drone’s behaviour is absolutely brilliant! To realise that not only do we fly some fantastic technology under great control, with live image feedback and recording of superb clarity but that the complete flight activity records are also available for subsequent review - similar to an aeroplane’s “black box”. And all of this at an affordable price (so far). Very impressive. Thanks for taking the time to provide (and explain) the very detailed analysis. ????

 

[GFields]

So sorry for your loss. Hope you had insurance or DJI refresh.

 

[Zbip57]

The only thing that is visible is some silver like really small metal piece inside rotors.

That looks like one of the magnets has come loose inside the bell housing. The black arrow points to one of the other magnets properly glued inside the bell housing. The red arrow points at the one that has come loose and jammed the motor.

 

[Bojan]

@gfieldsr thank you. I dont have insurance. But I am not so sad about it. I had really a lot of good time and videos and photos with it.
@Zbip57, yes something is stuck. I dont have a clue.
I just want to proof to my self. That I didnt do anything wrong. I couldnt stop it from hardware malfunction.
I am wondering. How many flights everyone else have with their Mini 1s.
Because it seems that Minis is desing for some specific flight time. And how much is that?

 

[BudWalker]

Ok ... if the mobile device DAT log FLY072.DAT is gone (which they usually are as they gets deleted once a sync to the DJI servers are made) ... the SD card fc_log.log will do.

The commands you made there just before the incident starts ... first full speed forward, then full break + full descent during the breaking + input for yaw with the rudder stick make it hard to interpret just from the AC movements, exactly which side that gives up & don't provide enough thrust ... so it's not the rear right side that causes this, instead the other CCW torquing side ... the front left.

This was the stick inputs you made alone, at 561,1sec you releases all sticks to neutral, but approx. a second later you at the same time apply 3 different stick inputs, rudder (yaw, CCW rotation), throttle (for descend) & a blip of elevator (for forward speed) ...
View attachment 133620

If we look at the RPM's for the 4 motor sides around 562,2sec, marked below... just when you get the message about "Motor Blocked". We see that just before that when you return all stick to neutral, the RPM's for all 4 motors rapidly decrease at first (most in the left front, blue graph). Then moments later after 562,2sec, 3 motors decrease their RPM even further (but not to the low level of the left front) ... this as a result of you starting to apply throttle inputs for descend. As you return the throttle stick to neutral again & momentarily stop the descent, 3 of the four motors increase the RPM again but not the left front ... & it's here you get the "Motor Blocked" message.

View attachment 133621

If we in relation to the motor RPM's in above chart check off how the flight controller actually wanted them to operate ... below you have the percentage of available RPM that is commanded by the FC. The blue graph that represent the left front motor goes to a 100% command at 562,4sec ... but as seen in the chart above the RPM (blue graph) doesn't increase at all.

View attachment 133622

So ... the left front motor doesn't obey the FC command to rev up the RPM from approx. 561.9sec. This could mean that it have got blocked either by a seized bearing or some debris.

To confirm the "blocked motor" theory further we can look at the current draw for the motors ... if a motor is stuck & can't rotate but is commanded to increase the RPM the current draw usually increases. And that is what we see in below chart where the left front (blue graph) spikes up higher than the other 3 motors.

In the end this shows that no bird was involved at all ... instead the front left motor got jammed for some reason & that caused it to quickly come tumbling & rotating down.

View attachment 133623

Here the sequence of events in a sat picture... The start of the painted black arrow is the left side of all charts shown above. The left front motor gets blocked at the red cross ... which induce a rotational torque unbalance which make the AC tumble & spin down along the dotted black painted arrow.

View attachment 133624

Where is the LikeX10 button when you need it? I was trying to figure out how you managed to adjust the time offset so that it matched the .txt log. You must've used the DatCon and specified the correct time offset?

 

[slup]

Where is the LikeX10 button when you need it? I was trying to figure out how you managed to adjust the time offset so that it matched the .txt log. You must've used the DatCon and specified the correct time offset?

Yep ?

 

[Made2Phly]

In light of this, I am thinking I should include a fairly detailed motor inspection every so many flight hours. Does anyone have any ideas/thoughts on this? How hard is it to appear inside of the motor?

 

[slup]

In light of this, I am thinking I should include a fairly detailed motor inspection every so many flight hours. Does anyone have any ideas/thoughts on this? How hard is it to appear inside of the motor?

It's hard to judge just from a visual inspection that a magnet for instance will come lose on the next flight. Disassembling thing's just to take a look ( even though you can't forecast any failure just by looking ...) just increases the risk that something gets damaged during the process or wrongly assembled again.

Instead I would recommend that you ...

-Check so that motor screws haven't come lose + check off the area around where the motors are attached on the arms for cracks repetitive.

-Inspect the props & attachment tabs after cracks or chipping repetitive.

-In the pre-flight check turn the motors & feel after notchiness & roughtness.

-See to that you take-off & land in a spot where it's clean & free of debris and dust.

If you suspect that dust & smaller objects can have found it's way into the motors, carefully blow them out with canned compressed air.

 

[Made2Phly]

I will add those items to check. The compressed air- i figure there will often be dust etc in the motors. I have resisted
the compressed air for fear of pushing stuff in to the innards of the motors, e.g. betwixt and between the fine copper winding. Thoughts?

 

[slup]

I will add those items to check. The compressed air- i figure there will often be dust etc in the motors. I have resisted
the compressed air for fear of pushing stuff in to the innards of the motors, e.g. betwixt and between the fine copper winding. Thoughts?

No need to blow them out on a regular basis ... only if you strongly suspect that dust & debris have entered, always better to prevent that from happening in the first place by using a landing pad or hand launch/land. The keyword is carefully, don't use full pressure from a close distance.

 

[Bojan]

I would just like to notice that its not 100% sure magnetic felt before this flight. Its possible magnetic plate felt with crash.