Hi,

My last test flight on the FlyApp 1.0.6. was not completely succesfull....
i had to grab my MM from the ground, and not at homepoint!
See the video.

On all other flights i did not have severe height droppings, blades are in good condition.
So less confidence in my MM, carefull now with yaw turns with low speed!



cheers
JJB

Well because it looked extremely windy that might be your or djis problem.

firmware is still 1.0.4 no? this 1.0.5 in the video is a typo i guess?

so overall conclusion is fly higher  than 10 m with wind but not too high, so you can overcome it

quite challenging to find perfect conditions for a beginner type of drone i guess..

Thanks for the capture. It looks very interesting. Much like my close call on xmas in China 2019 except this one is on grass and P mode. How are you certain the props are good? Some say bad props are not visually discernable to the eye.
Also did you throttle up to counter it?

It’s very disappointing that DJI continue to seemly ignore this issue, as with the propellers hitting the body also, I no longer fly over water or anywhere were I would struggle to retrieve my Mini, I have little confidence in it at the moment which is really said because it has the potential to be great.

Guorium Posted at 4-8 05:15
Thanks for the capture. It looks very interesting. Much like my close call on xmas in China 2019 except this one is on grass and P mode. How are you certain the props are good? Some say bad props are not visually discernable to the eye.
Also did you throttle up to counter it?

“Some say bad props are not visually discernable to the eye”


What like put them under a microscope ? if you can’t see defects it’s probably because there not there.

Hello JJB and sorry to hear about your unfortunate event... but weren't you doing that exactly in the hope of such an outcome ?

I mean... who's better than you here for looking at what happened to your MM during that flight ? Can you see what happened at that precise moment ?

How were the battery cell voltages ? Were the motors maxed out ? Reported battery level was quite low, I'd say far too low to stand against a wind at some point beyond the maximum capability of the Mini (that is 8 m/s).

hallmark007 Posted at 4-8 04:51
Well because it looked extremely windy that might be your or djis problem.

Nope, wind was max 10 m/s,  fluctuating.

And stopping the forward motion of my MM was possible, with too much wind it would drift in the same direction. And ofcourse if too much wind it should keep height and drift....

As seen on other logs, reducing speed and yawing = possible height drop.

cheers
JJB

sbonev Posted at 4-8 05:02
firmware is still 1.0.4 no? this 1.0.5 in the video is a typo i guess?

so overall conclusion is fly higher  than 10 m with wind but not too high, so you can overcome it

no type   in the log firmware = 1.0.5   will check this in the flyapp

Guorium Posted at 4-8 05:15
Thanks for the capture. It looks very interesting. Much like my close call on xmas in China 2019 except this one is on grass and P mode. How are you certain the props are good? Some say bad props are not visually discernable to the eye.
Also did you throttle up to counter it?

Props are OKE (i think), i always keep my MM unfolded. and before this i flew in this flight many minutes in sport mode with all kind of rapid moves etc, no problem at all.
And after update the FlyApp again flights with no problems.

To late for me to throttle up, when i looked at the screen i saw it has 'landed'....

My theory = wind in the tail, yawing and wind through the mini....seen that on other not mine flights as well. For me to be more aware of this possibilty at windy hover turns.

cheers
JJB

m80116 Posted at 4-8 06:21
Hello JJB and sorry to hear about your unfortunate event... but weren't you doing that exactly in the hope of such an outcome ?

I mean... who's better than you here for looking at what happened to your MM during that flight ? Can you see what happened at that precise moment ?

Well, the part before this in flight was done to test several things out.
This last part i wanted to fly back in sport mode along the wind, for seeing how much groundspeed.

Batt (both cells) at 33% > 3.3 volts, normal values.

Fully forward stick gave 26 degrees pitch down, so enough power to the motors.
Checked my DAT file, not sure if motors were at their max, ..see my chart.Checked : the moment the left way turn started the motors were spinning slower! so not at their max!


cheers
JJB

Thanks for posting this, it may help DJI to study the issue better and come up with a fix.
Personally I got bored of doing this "drop" tests myself, they did happen unintentioinally at first, then I found hard to replicate but it was still happening around 40 to 60% of attempts.
Just something to consider and whatch out for.

I can't evaluate the data properly because the temporal resolution (spacing) on the motor revolution graphs is too compact.

I tend to believe that since the Not Enough Force condition wasn't out this has very little to do with motors, battery level or deformed propellers.

It is the behavior already exhibited many times by the Mavic Mini when it encounters a deep variation of wind pressure exerted inside the body where the barometric sensor resides. A sudden stop with a wind condition outside the design limit exacerbated this effect. The sudden stop caused a pressure drop reading (which meant the AC was climbing rapidly) to which the FC responded accordingly commanding the motors to slow down.

I think it's the very well known and established uncommanded descent that I initially isolated during a test for several seconds down and forward in Sport mode. We'll wait for more data and evidence from JJB but as things stand right now I have no reason to believe otherwise.

hallmark007 Posted at 4-8 05:51
“Some say bad props are not visually discernable to the eye”

I don't know the story behind this photo, but these two props look very different to the naked eye:

Wow your drop looks the same as that guy's a week or so back at the soccer field, he was yawing and it dropped. I wish I remembered from his video if the yaw direction was the same as yours to maybe rule out if it's directionaly caused.

I know you said in your log it's 1.05 but you could check Dji assistant and see what it says?

I know from testing the mini if pushed upon from the underside it will ramp down in rpm to almost nothing. I wonder if the wind is causing enough upward pressure that it's causing the mini's legs to fall out from under it. I'm gonna try with a blower to see if it's possible to knock the mini out or stall it somehow, having done a lot of low water flying this week it's concerning to see it happen to a previously unaffected mini.

120ccpm Posted at 4-8 12:32
I don't know the story behind this photo, but these two props look very different to the naked eye:

[view_image]

That was my point you can see them with your eyes, I’m not certain props are the cause of this, I’ve tried only today testing and I can’t recreate this with my drone, But I have switched props around and it causes great bounce with the craft, I’ve seen people test props that had tips cut off on Mavic pro and you can still fly with them, I don’t believe that those props in the photo effect how the wind moves over and under them and if props are bad they are bad as soon as you are up in the air and this doesn’t seem to be what’s happening, it’s something maybe propulsion.

120ccpm Posted at 4-8 12:32
I don't know the story behind this photo, but these two props look very different to the naked eye:

[view_image]

We never really got insight to that photo or none that I could find, my front props look like the top picture while both my rear look like the bottom. Do we know if the bottom picture came from the back and the top from the front and not that it's actually a "bad" prop?

Looking for that slight upward bow I can see it in my slow mow video here: I'll check my spares to see if they have the same bow or not and report back later.

I had uncommanded descent and fall to the ground as well. I will report more later from my computer. But I changed rear props (no demage on old ones) and bird flyes well, over 10km distance since the prop change with no trouble. So I feel that props can be the weak point.

120ccpm Posted at 4-8 12:32
I don't know the story behind this photo, but these two props look very different to the naked eye:

[view_image]

thats a really good way to test the props for deformation, I just swapped all 8 of mine after i had the mini fall to the ground in a field the other week (my mini is only a few of weeks old), ill take some pics of the props i took off compared to some fresh packs I still have.

hallmark007 Posted at 4-8 05:51
“Some say bad props are not visually discernable to the eye”

It is mostly the pitch angle. If that is off by a few degrees from mishandling of the props or whatever, the thrust will be changed. A few degrees off is indeed not easily seen with naked eyes.

Guorium Posted at 4-8 15:13
It is mostly the pitch angle. If that is off by a few degrees from mishandling of the props or whatever, the thrust will be changed. A few degrees off is indeed not easily seen with naked eyes.

I don’t think that is the problem I’ve been using my props since I got mini on day one there is almost no wear and tear on them unless you’re landing in the grass or have knocked them there’s no reason to change them. I have an original Mavic pro with original props never changed and it flys great if props were the problem that would show up early in the flight, I have seen this descent coming after many minutes I’ve seen it in wind in no wind at 3m 20m and 50m bad props don’t get worse as you fly unless there nicked or similar.

hallmark007 Posted at 4-8 16:30
I don’t think that is the problem I’ve been using my props since I got mini on day one there is almost no wear and tear on them unless you’re landing in the grass or have knocked them there’s no reason to change them. I have an original Mavic pro with original props never changed and it flys great if props were the problem that would show up early in the flight, I have seen this descent coming after many minutes I’ve seen it in wind in no wind at 3m 20m and 50m bad props don’t get worse as you fly unless there nicked or similar.

I agree that something must have changed in the flight given the normal behavior up to the point of an unexpected landing. I can only say the prop could be one thing as it could have gone beyond functional shape momentarily under a set of conditions. These paper-thin plastic blades can go into oscillation given the correct uneven flow conditions. Oscillation of the props is known to cause off-design conditions severely affecting their performance.



Or something else totally unrelated to the props. We do not have evidence for any mechanism of failure. I really hope DJI can work this one out with their resources.

I don't understand why so many of you are ignoring what I believe is the most logical conclusion.

Since the battery level wasn't critical, afaik the motors weren't maxed out and were commanded to slow down instead... that is not the typical reaction of the FC when it encounters degraded lift (from warped propellers) and causing ESC nef state (which wasn't out).

For what I understand from JJB's report the motors were deliberately slowed down. It is already proven many times that is linked to sudden and vigorous wind changes, to which the most practical key of understanding is a temporary spurious barometric sensor reading. Something that is most probably inbred in the body design and sensor positioning in the Mavic Mini.

Had it had enough clearance it probably would have gotten a good chance of recovering from 1/3 to 3/4 of the altitude drop. It was doing a YAW turn after being stopped, exposed to a wind beyond the design limit of the Mavic Mini, no idea about the precise direction the wind was pushing... but this screams pressure variation from every angle I could see it. Small wonder it dropped...

I am not justifying anything... but it's a very borderline scenario. Being supplemented with this kind of data is a scenario that I would have expected...

Guorium Posted at 4-8 17:19
I agree that something must have changed in the flight given the normal behavior up to the point of an unexpected landing. I can only say the prop could be one thing as it could have gone beyond functional shape momentarily under a set of conditions. These paper-thin plastic blades can go into oscillation given the correct uneven flow conditions. Oscillation of the props is known to cause off-design conditions severely affecting their performance.
https://www.youtube.com/watch?v=5QAq7EeEC3Y

Thanks for this demo! I used to see that with the helicopters. I have stiffened the front arms and cannot see any errors in the logs during the toughest flight maneuvers. Flies great, so far ...

If I'm not mistaken, people have reported two type of unexpected altitude drops, with the MM:

1. Short drops, typically coming to a stop in S-Mode, fully recoverable (of course assuming you are not flying close to the ground). Theory is that sudden change in air pressure around the AC tricks the barometer, and the flight controller responds accordingly.
2. Full descents, unrecoverable, often linked to insufficient power error. Theory is that props have something to do with this, as some reportedly fixed the issue by replacing them. In my opinion, there is more to it as props don't go bad out of the blue, mid-flight. Maybe they (slowly) lose pitch and reach a point where the flight controller needs to max out the motors to keep the AC in the air, which triggers some sort of limp-mode, slowly bringing the AC down. Another option is that there is a true hardware problem, and the flight controller cannot keep the AC level without losing altitude.

To me, JJB's case seems more like a #2, no? The AC was basically stationary when it happened, and the drop was quite significant (10 meters). Moreover, the barometer appears to be perfectly working, as the height is correctly reported by DJI Fly. If this were a drop induced by false barometer readings, wouldn't we see inconsistencies in the height, as it's reported by the app (vs. actual)?

Guorium Posted at 4-8 17:19
I agree that something must have changed in the flight given the normal behavior up to the point of an unexpected landing. I can only say the prop could be one thing as it could have gone beyond functional shape momentarily under a set of conditions. These paper-thin plastic blades can go into oscillation given the correct uneven flow conditions. Oscillation of the props is known to cause off-design conditions severely affecting their performance.
https://www.youtube.com/watch?v=5QAq7EeEC3Y

I’ve been experimenting with my prop strike issue, I find if I add tape to the front legs and stiffen the plastic the Mini develops a resonant frequency that manifests in the props by +/- 3-4mm (8mm total movement)

TDZHDTV Posted at 4-8 22:57
I’ve been experimenting with my prop strike issue, I find if I add tape to the front legs and stiffen the plastic the Mini develops a resonant frequency that manifests in the props by +/- 3-4mm (8mm total movement)

Adding tape caused it? Really?

120ccpm Posted at 4-8 21:44
If I'm not mistaken, people have reported two type of unexpected altitude drops, with the MM:

1. Short drops, typically coming to a stop in S-Mode, fully recoverable (of course assuming you are not flying close to the ground). Theory is that sudden change in air pressure around the AC tricks the barometer, and the flight controller responds accordingly.

Hi 120ccpm,

With #2 motors are spinning full speed, trying to stop the decsend.
In my case motors were spinning down during descend.
Barometer indicated the correct values, it all depends where this signal is from...
if the baro signal goes to the IMU to Indicator, than the caculation part of the signal in IMU / FC processing can go wrong and  still indicates correct values.

I agree on your #1 ; MM is not that height hold steady when pitching full down to up and v.v.  

cheers
JJB

TDZHDTV Posted at 4-8 22:57
I’ve been experimenting with my prop strike issue, I find if I add tape to the front legs and stiffen the plastic the Mini develops a resonant frequency that manifests in the props by +/- 3-4mm (8mm total movement)

I have glued plastic inserts firmly. The arms are like the back ones. I also cannot see any unexpected flight movements, basically flies like the MP, only not as fast ... What exactly is the maneuver that leads to the mistakes here?

Guorium Posted at 4-8 23:23
Adding tape caused it? Really?

I added UHMW tape as it does not stretch, the result was significant deflection in the propellers and a shift in acoustic noise...  Mini wasn’t happy at all in hover.

I wonder if anyone who can repeat these drops has a gimbal sun shade cover, it would be interesting to tape it closed and see if sensors still get confused.  I have one of these covers but to date have not suffered drops... only prop strikes.

fans2b25c744 Posted at 4-8 18:20
I don't understand why so many of you are ignoring what I believe is the most logical conclusion.

Since the battery level wasn't critical, afaik the motors weren't maxed out and were commanded to slow down instead... that is not the typical reaction of the FC when it encounters degraded lift (from warped propellers) and causing ESC nef state (which wasn't out).

Hi,

MM was not exposed to too much wind ; firstly it did not drift away when stopped the forward motion.
(btw, flying forward into the wind)

I read in the DAT file a wind speed of 6 m/s.

As said, i did not throttle up as i was looking at something else for short time....convinced that during this left yaw turn my MM would hold its height (as it should do ofcourse!)

So for me the only change is situation is that the wind blowing from behind (during this fwd flying) along the MM now entered from the left side through the MM.

cheers
JJB

Hi there, sorry for the inconvenience, could you please provide us with more details for further analysis if possible:
1. The firmware version of the aircraft and the remote controller?
2. The APP version?
3. The model and the OS version of your phone?
4. Flight logs under DJI Assistant 2 for Mavic (https://www.dji.com/mavic-mini/downloads) -- Log Export--Save to local. Please upload to Google Drive or Dropbox and then post the link here.

TDZHDTV Posted at 4-9 00:23
I added UHMW tape as it does not stretch, the result was significant deflection in the propellers and a shift in acoustic noise...  Mini wasn’t happy at all in hover.

Got video?

JJB* Posted at 4-8 23:24
Hi 120ccpm,

With #2 motors are spinning full speed, trying to stop the decsend.

JJB:
if the baro signal goes to the IMU to Indicator, than the caculation part of the signal in IMU / FC processing can go wrong and  still indicates correct values.

I think it's the latter. What we see is what is being computed out  from an algorithm, one mod reported that not only height is measured by baro but also by GPS (which I believe should have very marginal effect) but anyway...

Don't let me digress. Props don't go bad out of the blue by they go with time (and storage most probably), and begin causing ESC nef errors. Not the case here... and anyway you have flights plagued by ESC errors without a single drop, but there's always a non-return point, a threshold that once past it the drop does actually happen... basically the point it couldn't handle anymore.

I am not thinking this is JJB's case since he would have known and taken action before that happened.

JJB* Posted at 4-8 23:24
Hi 120ccpm,

With #2 motors are spinning full speed, trying to stop the decsend.

With #2 motors are spinning full speed, trying to stop the decsend.

Are you 100% positive that in case of the unrecoverable descent, all motors are still spinning at full speed? Is that visible from the logs? I don't see RPM values in the TXT flight records.

I honestly find it hard to believe, as that would point at the props being all faulty, the same way and at the same time. I could see a prop losing pitch (thrust) with time, up to the point the AC has trouble flying, but these uncontrolled descents happen right in the middle of a perfectly normal flight. Gut feeling is that there's more to it than just props.

Guorium Posted at 4-9 01:04
Got video?

No unfortunately I didn’t record it, I’m still experimenting so will capture if I get the effect again

I flying almost everyday in extreme wind condition up to 10-13 m/s. Sometimes my Minic even can't fly at all in sport mode and hardly keeping it's place (I understand all responsibility and fly in clear places) BUT, thanks God, I never have this kind of problem. I think this kind of sh@t happens because of defective Minics. DJI must acknowledge these cases so users will not try to fly again after "falling from the sky" cases but send drones back for replacement.

This drop in height looked dangerous. Really awaiting DJI to solve this issue.

@JJB Can you please post the log here?