Sudden descent and uncontrolled landing in strong wind

Ian in London · Nov 15, 2020

Hello all
This afternoon I was testing the original Mini in strong wind of around 20-25 mph as part of a wind comparison test with the Mini 2 I was filming.
The Mini was clearly struggling and was flashing up the vibrating wind warning telling me to reduce altitude and land, which I ignored because I was specifically trying to test the wind handling. However in a first for me, twice the Mini suddenly dropped altitude from around 10 metres / 33 feet and actually dropped to the ground. Both times I was keeping the left stick up, but it kept descending. First time it bounced up off the grass and rose up again; I flipped into Sports mode and flew for another 2 minutes or so before it did the same thing; dropped from 10 metres in a around 10 seconds and this time shut down as the props got blocked in soil.

I've checked the flight logs on AirData.com and cannot see any error or command that would have prompted the two descents.
Battery was still at 40%; this happened very close to take off point; full 100% signal. According to AirData, the wind was around 15 - 20 mph; I've certainly flown the Mini in stronger wind.
Anyone had this happen on their Mini before?
Cheers
Ian

boblui · Nov 15, 2020

The "propellers rotating too fast" warning messages in your log suggest that you encountered the well-known uncommanded descent problem of the Mini. Some of the props are probably deformed making them unable to produce sufficient thrust.

When there is wind, the craft needs to use extra power to fight against the wind and the remaining thrust is insufficient for maintaining the altitude hence the descent. Their locations are indicated by the beeping motors after the craft is landed. Just replace the props on those motors. The problem should go away.

Nonprophet · Nov 15, 2020

boblui said:
The "propellers rotating too fast" warning messages in your log suggest that you encountered the well-known uncommanded descent problem of the Mini. Some of the props are probably deformed making them unable to produce sufficient thrust.

When there is wind, the craft needs to use extra power to fight against the wind and the remaining thrust is insufficient for maintaining the altitude hence the descent. Their locations are indicated by the beeping motors after the craft is landed. Just replace the props on those motors. The problem should go away.

It will be interesting to see if the Mini 2 suffers from the same problem.....

boblui · Nov 15, 2020

Nonprophet said:
It will be interesting to see if the Mini 2 suffers from the same problem.....

There has been reports that the Mini 2 has stiffer ( and heavier ) props so it probably doesnt have the same problem.

Deleted member 103366 · Nov 15, 2020

Also was it facing forwards or backwards? If you replay the flight in the app you may see some warning you missed.

Nonprophet · Nov 15, 2020

I guess time will tell....

boblui said:
There has been reports that the Mini 2 has stiffer ( and heavier ) props so it probably doesnt have the same problem.

Ian in London · Nov 15, 2020

boblui said:
There has been reports that the Mini 2 has stiffer ( and heavier ) props so it probably doesnt have the same problem.

The Mini 2 props are much stiffer. Thanks for the heads up on the props; admittedly I've been ignoring that error as it's been there ever since a certain upgrade many months ago.
Surprisingly I was reluctant to do the wind test today as I didn't think it windy enough to do a proper test

As it was, I had to go traipsing around a muddy field to retrieve the Mini....
I'll replace the prop in question. Yes, I have the combo and have always stored it in th bag.....

scro · Nov 16, 2020

Definitely sounds like the "uncommanded descent" issue. I seem to recall a video you did recently with the Mini 1 in wind, and at the end of the flight at least one of the motors was beeping as the firmware had detected it was running too fast - this is a fairly sure sign of damaged or squashed props and almost always happens on the rear props.

Testing the Mini in very strong wind

We've had a couple of big Atlantic storms rolling in over the last week and I took the opportunity to push the Mini to its limits flying in very strong wind; with a few tricks you can re-control it when it starts to blow away... Cheers, Ian

mavicpilots.com

Get them props changed and either stop using the FMC case or be very careful when you fold up the props. I have the FMC case and keep my drone stored in it but am quite pedantic about ensuring the props are very carefully folded in pairs, with L and R prop pairs not overlapping, and both pairs sitting fwd of the power button. I'm still on the original blades after 1 yr of ownership, and with the drone spending nearly all of its non-flying time in the FMC case.

hiflyer201 · Nov 16, 2020

I know people love the Mini..but I really think that DJI should have re-called them. It sound to me like the old...there are those that have..and there are those that will.

DanMan32 · Nov 16, 2020

That would have been a way too expensive proposition for the maybe 1% that encounters the uncommanded descent that really can be prevented if the props are properly cared for. I too have had the MM1 for a year, storing it in the FMC case with overlap without issue. The stress with overlap is negligible to me, compared to it dangling toward the back where it gets squashed by the bar that holds the AC in place in the case.

For my M2, I remove the props when storing in the FMK case for concern of warping them.

Ian in London · Nov 16, 2020

scro said:
Definitely sounds like the "uncommanded descent" issue. I seem to recall a video you did recently with the Mini 1 in wind, and at the end of the flight at least one of the motors was beeping as the firmware had detected it was running too fast - this is a fairly sure sign of damaged or squashed props and almost always happens on the rear props.

Testing the Mini in very strong wind

We've had a couple of big Atlantic storms rolling in over the last week and I took the opportunity to push the Mini to its limits flying in very strong wind; with a few tricks you can re-control it when it starts to blow away... Cheers, Ian

mavicpilots.com

Get them props changed and either stop using the FMC case or be very careful when you fold up the props. I have the FMC case and keep my drone stored in it but am quite pedantic about ensuring the props are very carefully folded in pairs, with L and R prop pairs not overlapping, and both pairs sitting fwd of the power button. I'm still on the original blades after 1 yr of ownership, and with the drone spending nearly all of its non-flying time in the FMC case.

Yes, will be changing them as it was pretty sudden and with no warning that it was actually descending.....

Thanks very much all.

Ian

Tiger64 · Nov 16, 2020

I had similar thing happen this morning. Replaced props and it was sweet

icecoldgin · Nov 16, 2020

Props on the Mini (and even the Mini 2 I would say) are prone to deformation when it is not protected properly in its case.

That is why one of the first accessories I got were the propeller holders. Now, the Mini and its props rests snuggly in the camera bag .

And, by way of indirect admission as to the fragile nature of these props, DJI now even included the propeller holders in its Mini 2 FMC. ?

DanMan32 · Nov 16, 2020

I don't understand how the DJI can work well, since the strap presses down on the front props resting on the top of the AC.

Ian in London · Nov 22, 2020

scro said:
Definitely sounds like the "uncommanded descent" issue. I seem to recall a video you did recently with the Mini 1 in wind, and at the end of the flight at least one of the motors was beeping as the firmware had detected it was running too fast - this is a fairly sure sign of damaged or squashed props and almost always happens on the rear props.

Testing the Mini in very strong wind

We've had a couple of big Atlantic storms rolling in over the last week and I took the opportunity to push the Mini to its limits flying in very strong wind; with a few tricks you can re-control it when it starts to blow away... Cheers, Ian

mavicpilots.com

Get them props changed and either stop using the FMC case or be very careful when you fold up the props. I have the FMC case and keep my drone stored in it but am quite pedantic about ensuring the props are very carefully folded in pairs, with L and R prop pairs not overlapping, and both pairs sitting fwd of the power button. I'm still on the original blades after 1 yr of ownership, and with the drone spending nearly all of its non-flying time in the FMC case.

Props changed and problem solved.
And for those who aren't sure about changing the props, here's the vid....

https://youtu.be/ngOuPuRGhLQ

maelstrom · Nov 22, 2020

hiflyer201 said:
I know people love the Mini..but I really think that DJI should have re-called them. It sound to me like the old...there are those that have..and there are those that will.

There must be tens (hundreds?) of thousands of Minis flying worldwide. Complaints on the Internet always make issues seem much more common than they usually are. If the apparent “uncommanded descent” issue was as a result of a design problem, most Mini owners would be experiencing it and that doesn’t seem to be the case - I’ve certainly not experienced it.

If you look through the posts analysing crashes on this forum, the vast majority of them turn out to be pilot error. This is as true for the Mini as it is for any other drone.