uncommanded descent

[rscheff]

As my Mavic Mini increasingly has problems with keeping altitude when flying at full speed I want to ask you to do a little test with yours to check if this problem is affecting all Mavic Minis more or less:

1. Go to a flat location with at least 200m free space in one direction.
2. Take off in P mode and go to a preferred altitude, keep the altitude as shown within the Fly app in mind. Don't touch the throttle stick anymore from now on.
3. Fly straight away approx. 200m with full speed, then slow down for hovering.
4. Read the altitude there, then wait about 10s and check for uncommanded altitude loss.
5. Turn 180° and fly back to your home point with full speed.
6. When back, check the altitude as displayed by the Fly app. Is it still the same as was at the beginning, or how far is it off?
7. Switch to Sports mode and repeat from step 2.

Please let me know your results.

I just performed those tests that you requested. Keep in mind it was a little gusty but not enough to not fly. I made several back and forth runs in regular mode. First run started at 2.6 feet and ended at 2.3 feet and after approx. 10 seconds the drone went to 7.2 feet. 2nd try start at 3.3 feet, stopped at 5.9 feet and after 10 seconds dropped to 4.9 feet. 3rd run started at 4.9 feet, ended at 9.8 feet and dropped to 8.2 feet. 4th run started at 2.0 feet ended at 5.9 and dropped to 4.5. 5th run started at 7 feet and ended at 11 feet and dropped to 3 feet. Switched to sport mode. Started at 2.6 feet ended at 7 feet and dropped to 4.5 feet. 2nd run started at 8 feet and ended at 9 feet and dropped to 3 feet. 3rd run started at 1.5 feet, ended at 5.5 feet and then an uncontrolled bounce off the ground but still remained hovering at what appeared to be 1 foot but the controller said 3 feet. Stopped flying at this point. Should be noted that I made home base on the ground and even when the drone hovered at a consistent height (lets say 2.5 feet) the remote would say all different heights from 1 foot to 5 feet. My original post I had a problem with the drone listing to the right, the left side was higher than the right. This went away after a couple flights. People were suspecting that the props were getting squashed while in the storage box. I purposely left drone sitting on a table overnight and when I made the first flight this morning it was listing to the right again but by the end of the testing it was level again. I will try the tests again if the wind dies down. There seems to be no consistency in the start and end heights and this is the first time that I had an uncontrolled descent, good thing it was only a couple feet off the ground. Do you know if anyone is reporting this stuff to DJI? Do you think I should report this test to them just in case I loose the drone.

 

[rscheff]

As my Mavic Mini increasingly has problems with keeping altitude when flying at full speed I want to ask you to do a little test with yours to check if this problem is affecting all Mavic Minis more or less:

1. Go to a flat location with at least 200m free space in one direction.
2. Take off in P mode and go to a preferred altitude, keep the altitude as shown within the Fly app in mind. Don't touch the throttle stick anymore from now on.
3. Fly straight away approx. 200m with full speed, then slow down for hovering.
4. Read the altitude there, then wait about 10s and check for uncommanded altitude loss.
5. Turn 180° and fly back to your home point with full speed.
6. When back, check the altitude as displayed by the Fly app. Is it still the same as was at the beginning, or how far is it off?
7. Switch to Sports mode and repeat from step 2.

Please let me know your results.

I posted a rather lengthy reply with test results and I do not see it here, did you get it? I basically had start and stop elevations that were pretty far apart, for example start at 2 feet and end up at 7 feet. I also had 1 uncontrolled descent to the point where the drone bounced off the ground. I then thought to check the logs and they did not show any of the radical altitudes or the crash. I will try again later today when it warms up maybe the cold here in Massachusetts had something to do with the radical altitudes but I do not understand the lack of evidence in the logs.

 

[GerdS]

Hi,
Thank you all so far for doing my test. Here it was also gusty today, but I did my test again, just with my old Mavic Pro, also both in P- and S mode.
What shall I say? Altitude was exact same between start and end of test, if there was any derivation it was less than 1m.
Same I would expect from Mavic Mini. The FC executes many control loops and one of them is responsible for continuously adjusting altitude. Something goes very wrong there in firmware, but for some MMs the problem does not show up that seriously, why ever...

The problem is now finding a really competent contact person at DJI who is able to adress this problem to the responsible developer for finally fixing.
Any help or contact info is welcome.

 

[rehkram]

Re the design goal of keeping the weight down possibly being the genesis of the problem, absolutely, point taken. Actually 249 g. Keeping the price down could also have been in play.

 

[rehkram]

I flew Gerd's test profile several times, at several different start altitudes from 15 ft to 30 ft. It was windy which has been the pattern around here for a week or more. UAV Forecast showed 14 mph gusting 29 mph, yikes. I flew the outbound legs into the wind. It was being buffeted pretty hard while hovering and working to stay in place. I did not see the very high revving followed by sinking at any point.

To cut a long story short I was gaining ~10 ft in altitude by the end of each run, in both modes, at all the start altitudes I flew. So at the end of each return leg it was ~20 ft higher than at the start.

For comparison I want to fly it again in zero- or slight wind, which could be tomorrow.

I actually think this is a separate issue to the uncommanded descent thing, unless there is a common factor involved, the fixing of which could solve both issues.

I'm looking on the bright side; at least it's going higher, not lower! Can't believe I hadn't even noticed it before but I tend to follow the topography of my land (hilly) and seldom, if ever, want to maintain a set altitude. Until today.

 

[KiloMeater]

I am sorry for the slight off topic , I hope I will be excused as a newbie
How do you generate these very informative graphs with drone moves per axis, or output per individual motor?
I got so far to upload logs to AirData, I even bout a basic 360 subscription but I can nowhere find how to visualize in such details my drone’s flight log data.

 

[Keule]

how to visualize in such details my drone’s flight log data.

That's been done by 3rd party tools.
Look at following thread:

Mavic Flight Log Retrieval and Analysis Guide

With the introduction of the Mavic Mini there has been a noticeable uptick in the number of posts requesting help with lost or crashed aircraft. While there is plenty of help and advice available on this forum, and detailed guidance and options on several other websites, I thought that perhaps a...

mavicpilots.com

Proceed to topic: 4. LOG FILE CONVERSION AND VISUALIZATION

 

[GerdS]

I have analysed my latest test flight with CsvView and here you can see the result of my S mode flight.
During a full speed flight over about 250m my MM has ascended about 13m without touching the throttle stick.
This is totally unacceptable and I am not used to such bad behaviour from any DJI drone before.
I have attached the corresponding .dat file below.

Btw. I also tried the same course with my old Mavic Pro from 2016, also in S mode. And the difference in altitude from the beginning and after return was less than 1m! Same expectations I have for the Mini.

 

[FoxhallGH]

Forgive me for not being the best at getting the info from these graphs, but do you have any way of seeing what the motor rpm's were during the 'uncommanded' movements??

 

[sar104]

Forgive me for not being the best at getting the info from these graphs, but do you have any way of seeing what the motor rpm's were during the 'uncommanded' movements??

The motor speeds are in the DAT file, but not shown on that graph.

 

[GerdS]

There was nothing special with motor rpms, especially no overload warnings.

 

[rscheff]

I have analysed my latest test flight with CsvView and here you can see the result of my S mode flight.
During a full speed flight over about 250m my MM has ascended about 13m without touching the throttle stick.
This is totally unacceptable and I am not used to such bad behaviour from any DJI drone before.
I have attached the corresponding .dat file below.

Btw. I also tried the same course with my old Mavic Pro from 2016, also in S mode. And the difference in altitude from the beginning and after return was less than 1m! Same expectations I have for the Mini.

View attachment 99200

If I can refresh your memory, I performed your tests and had the same results but there was no consistency as to how much higher the drone ended up. I also had an issue with the drone listing to the right (higher on left) with very little wind. This listing went away after a few runs. But the height discrepancy got worse the more I flew it and the height discrepancy was always higher on the return run. I had ordered some new blades from DJI and had put them on when I noticed the listing. The listing and your observation of the drone climbing 8 feet got me to testing. Today I put the old blades back on and I had no listing but I still had an uncontrolled climb, but on the away trip it stopped at 8 feet off the ground then went down by itself to 3 feet. I had started at 2 feet. When the drone made the return trip it again rose to 8 feet but did not drop at all. This is my first decent drone (Mini) had toy ones but they had no control at all. I was not sure what to expect but I have to agree with you and your vast experience, this is not acceptable. I am now a little afraid of going too high (legally) or too far, especially since I experienced the uncontrolled descent to the point that the drone bounced off the grass. The strange thing is that the logs did not appear to show any of these problems, especially the crash. I wrote DJI a couple days ago and reported my test results just to put them on notice incase my drone makes a 100 foot crash. It would be nice if everyone performed these tests and reported to DJI, maybe something would be done.

 

[Meta4]

It would be nice if everyone performed these tests and reported to DJI, maybe something would be done.

DJI will have been getting reports of these incidents every day this year.
The evidence of the problem is abundant but they still haven't said a thing or announced any fix for the issue.

 

[GerdS]

I also have sent all my information to them via the contact page on DJI.com, awaiting their response now.
Actually I don't put any trust into the MM and when flying, I am avoiding any critical situation, e.g. flying above water, trees or other inaccessible area.

While this serious bug is still unfixed I cannot recommend buying a Mavic Mini any longer.

 

[rehkram]

Question. Are we all using OEM Dji prop blades & screws when flying these tests? I, for one, was using third party props.

To level the playing field, and also attempt to eliminate or confirm a potential cause, I've just ordered two sets from Dji. I'll report back when I've flown the test again with the brand new Dji props and screws.

 

[GerdS]

I am using original DJI blades only.

 

[rscheff]

It is ironic GerdS that you mentioned ordering new blades. That is just what I did that started me questioning it's performance. As soon as I put new blades on I started getting a list. I put back the old blades and the list is gone, and the drone seems to be a lot quieter. I sent an e-mail to DJI and this was their response:


Dear Robert,

Thank you for contacting DJI Technical Support.

We appreciate your time and effort in bringing this inquiry. We will be happy to help you.

We want to thank you for your continuous patronage of DJI products. We will do our best to help you and check our resources to provide the best possible solution.

Regarding your concern, let us try to isolate the issue first by doing some basic troubleshooting. Please follow the steps below.

1. Please make sure that both the app and the aircraft's firmware is updated.
2. Please do the calibration again and then try again.
3. Please make sure that there's no magnetic interference in the area.
4. Restart the aircraft.
5. Change location.

After all the troubleshooting and the issue still persists, we suggest sending the unit to our facility for further diagnosis. Kindly provide us the needed information below so that we can create a repair case for you manually.

Complete Shipping Address (No PO Box addresses. Kindly send us your complete shipping address to avoid further issues for shipping):

- House/Flat No./Building and floor:
- Street:
- City/Town:
- Province/State:
- Postal/Zipcode:
- Country:

We look forward to your response."

Now I ask the experts here, what do I do. I do not want the drone gone for months, I have heard that since (and maybe even before) Covid 19 their response time is in the months. I am also concerned that none of my flight logs appear to show the inconsistency in flight or even the uncontrolled descent or ascents. I told them in my letter that I just wanted to file this test as a matter of evidence that I have had problems with uncontrollable descents and ascents. I really do not want to give up the drone for months. I fly it almost daily, and I just got it a couple weeks ago. If I don't return it do you think that will void my warranty? I also bought the insurance package. Keep in mind when I performed these tests a couple days ago I had done all the callibrations and I have the current software. I would like to perform the tests again but the weather here is almost hurricane conditions.

 

[GerdS]

Robert, I didn't ask you for ordering new blades. I still have my first original set in use and as they are neither damaged nor bended there is no need for exchaning them.
No idea how long DJI repair or exchange will take in your region. I have filed my information to DJI yesterday but except for a automatic confirm mail I have not heared from them yet.
I would also not be happy if I would have to give it away for months, but 2 weeks or so would be ok as I cam still fly my old Pro in the meantime.

 

[rumitcu]

It is ironic GerdS that you mentioned ordering new blades. That is just what I did that started me questioning it's performance. As soon as I put new blades on I started getting a list. I put back the old blades and the list is gone, and the drone seems to be a lot quieter. I sent an e-mail to DJI and this was their response:


Dear Robert,

Thank you for contacting DJI Technical Support.

We appreciate your time and effort in bringing this inquiry. We will be happy to help you.

We want to thank you for your continuous patronage of DJI products. We will do our best to help you and check our resources to provide the best possible solution.

Regarding your concern, let us try to isolate the issue first by doing some basic troubleshooting. Please follow the steps below.

1. Please make sure that both the app and the aircraft's firmware is updated.
2. Please do the calibration again and then try again.
3. Please make sure that there's no magnetic interference in the area.
4. Restart the aircraft.
5. Change location.

After all the troubleshooting and the issue still persists, we suggest sending the unit to our facility for further diagnosis. Kindly provide us the needed information below so that we can create a repair case for you manually.

Complete Shipping Address (No PO Box addresses. Kindly send us your complete shipping address to avoid further issues for shipping):

- House/Flat No./Building and floor:
- Street:
- City/Town:
- Province/State:
- Postal/Zipcode:
- Country:

We look forward to your response."

Now I ask the experts here, what do I do. I do not want the drone gone for months, I have heard that since (and maybe even before) Covid 19 their response time is in the months. I am also concerned that none of my flight logs appear to show the inconsistency in flight or even the uncontrolled descent or ascents. I told them in my letter that I just wanted to file this test as a matter of evidence that I have had problems with uncontrollable descents and ascents. I really do not want to give up the drone for months. I fly it almost daily, and I just got it a couple weeks ago. If I don't return it do you think that will void my warranty? I also bought the insurance package. Keep in mind when I performed these tests a couple days ago I had done all the callibrations and I have the current software. I would like to perform the tests again but the weather here is almost hurricane conditions.

Hi Robert,
I experienced uncommanded descents (see More Mavic Mini Uncommanded Descents) and based on other's experiences, I contacted DJI who asked me to send the drone in for warranty service. Note that my drone was not damaged by the descents (despite the fact that it bounced off my driveway at high speed), so I was not looking for a warranty replacement or to use one of my DJI Care Refresh replacements. I was simply trying to "help the cause" of having an unreliable drone.

After contacting DJI, I received a similar email as yours above that resulted in me sending my Mini into DJI Service. As my thread states, DJI said they analyzed the data, concluded that the descent was due to flying with prop guards (not true) at high altitude (true), and suggested that I can pay them for a replacement unit! Crazy! Unlike other people who have said that DJI simply replaced their drone, they absolutely refused to acknowledge any issue on their end despite how much I tried to explain the situation to them. Ultimately, I asked them to ship the drone back to me. All told, it was gone for <3 weeks.

So in my opinion, it is not worthwhile for you to send your Mini back to DJI.

Regards,
Pat

 

[rscheff]

Robert, I didn't ask you for ordering new blades. I still have my first original set in use and as they are neither damaged nor bended there is no need for exchaning them.
No idea how long DJI repair or exchange will take in your region. I have filed my information to DJI yesterday but except for a automatic confirm mail I have not heared from them yet.
I would also not be happy if I would have to give it away for months, but 2 weeks or so would be ok as I cam still fly my old Pro in the meantime.

My point about the blades was I was flying with the original blades and did not notice any issues but I had ordered NEW blades and decided to put them on and see if there was any difference in flying, that is when the drone started listing and got extremely noisy. I put the original blades back on and the list was gone and now much quieter. I did not contact DJI for that purpose (blades) I had performed your tests and I was not happy with the results and contacted DJI to say that I think there is something wrong. You can even see the uncontrolled ascent and then descent in a video.