Mavic Mini uncommanded descent tests

[FoxhallGH]

This only confirms once again that social media is indeed a very powerful means to advertise products.

My experience is the opposite. I only use the original flymore case for storing my Mini and it never exhibited the uncommanded descent problem.

As described in my thread on the subject, I have intentionally flattened the props to create the problem so I know how much stress is needed. This knowledge is first-hand and acquired through hands-on practice, not hear say on "this and other Facebook forums".

There is absolutely NO ways that the tiny stress created by folded props pressing lightly against each other can create the following pitch difference which is about the minimum needed to make uncommanded descent happen :

View attachment 115354

And yet, it happens ... How come the DJI cure - and the most common cure for the problems this causes is for DJI to replace - or suggest the owner replaces - the props?
[I can assure you that I'm not advertising any products on Social Media ... The carry case I show above has no manufacturer details to enable any order to be placed, I simply use it to show that there is an alternate way to stow the Mini which does not mesh the props across the body].
At the end of the day however, I'm not on a crusade and don't consider it a responsibility to change your way of doing things - If you are happy with your Mini - Great! Go & Fly and have fun ...

 

[FoxhallGH]

But my comment still stands - if the case was causing these problems, why isn't everyone who uses it getting them? The problem is more likely caused because some people don't fold the blades exactly as recommended in the DJI diagram.

To be really picky about this point, do you fold the Mini up as shown by DJI's diagram?? ... One of our Forum members has pointed out that the diagram is impossible to achieve as the prop's would have to have the reverse spin and pitch to achieve exactly what DJI show ... Just as an observation, can you 'actually' exactly match the DJI diagram??? I'd like to know.

 

[Zbip57]

The problem is more likely caused because some people don't fold the blades exactly as recommended in the DJI diagram.

I think we can all agree that it's not even possible to fold the blades exactly as shown in DJI's diagram. Whoever created that diagram made an obvious mistake in how the blades (A&B) of the left-rear motor are depicted, shown with A fitting underneath B.



It would certainly damage the blades if forced to store the leading edge of blade-A under the trailing edge of blade-B.



Contrary to DJI's diagram, the blades can only be nested as shown above. With blade-A above blade-B.

Overlooking that obviously impossible discrepancy, the diagram is otherwise accurate. Fly More Combos, and non-Flymore Minis, both are indeed shipped with the blades folded as shown, with the left-rear motor's blades trapped between the Mini's body and bent under the right-rear motor's blades.

That is why, sometimes even reported on brand new Minis straight out of the box, it is most often the left-rear motor triggering the Motor Speed Error identifying the left-rear blades as defective and in need of replacement.

Ha!
FoxhallGH beat me to it.

 

[Zbip57]

What's more convincing to me is that the if the props are NOT folded up in that way, the inner side of the storage case will be pressing onto the prop with a much bigger force. The chance of getting the props flattened will be much higher.

Yes. Obviously it's not good to have the Mini stored with its weight resting on the prop blades.

In this image, with the blades turned outward, you can clearly see the angle at which the rear motors are mounted.


And in this image you can see how far the rear blades normally extend below the body of the Mini when turned inwards.



This third image shows how much the blades would be bent with the weight of the Mini resting on them.



The last image above shows the blades deflected tight against the bottom of the Mini's body. That's as far as they'll bend. It doesn't matter one iota whether that deflection is caused merely by the weight of the Mini resting on the blades, or whether the blades are being held in this position because they've been sloppily misplaced when inserting the Mini into it's carrying case. The point is, the blades are obviously being bent while in this position and that's as far as they'll go.

Can we not agree that storing the blades in this position is detrimental?

The Fly More Combo case does feature a trough deep enough for the blades to hang into, which in theory should accept them without deflecting the blades if the Mini is stored "properly" according to DJI's diagram. That should work beauty fine.

However...

In order to actually fit the rear blades into that trough, the blades first need to be nested together (crossed over each other) laterally across the body of the Mini. When folded together, the blades from one side must bend to fit under the blades of the other side. When stored according to DJI's diagram, the left-rear blades are again bent against the underside of the Mini, exactly as far as they are in the previous image above where the weight of the Mini was resting on them.

This image below shows how far the left-rear blades must bend in order to fit nested under the right-rear blades. Blade-1 is standing undeflected. Blade-2 is being bent down to force it under the opposite side's blades. Note it is already touching the body of the Mini. To fit both blade-1 and blade-2 under the opposite side's blades requires pressing them against the body of the Mini.

Yes, the tips of the (un-numbered) right-rear blades will droop nicely unimpeded into the trough designed for them in the Fly More case. But the left-rear blades are again being bent exactly as if the full weight of the Mini was resting on them. Is this not equally detrimental?

This theory does not make sense to me. The props are just lightly pressing against each other when folded up in that way and if there is any bending at all, it's barely noticeable.

If your props are only lightly pressing against each other, I suggest that they're already permanently bent as new straight blades cannot be positioned like this without forcing them to bend.

I just cannot see how that can result in the amount of pitch change required to trigger uncommanded descent.

And yet you have no problem seeing how similarly bent props (due to incorrect storage) would be more likely to trigger this condition?

 

[FoxhallGH]

Yes. Obviously it's not good to have the Mini stored with its weight resting on the prop blades.

In this image, with the blades turned outward, you can clearly see the angle at which the rear motors are mounted.
View attachment 115368

And in this image you can see how far the rear blades normally extend below the body of the Mini when turned inwards.

View attachment 115369

This third image shows how much the blades would be bent with the weight of the Mini resting on them.

View attachment 115370

The last image above shows the blades deflected tight against the bottom of the Mini's body. That's as far as they'll bend. It doesn't matter one iota whether that deflection is caused merely by the weight of the Mini resting on the blades, or whether the blades are being held in this position because they've been sloppily misplaced when inserting the Mini into it's carrying case. The point is, the blades are obviously being bent while in this position and that's as far as they'll go.

Can we not agree that storing the blades in this position is detrimental?

The Fly More Combo case does feature a trough deep enough for the blades to hang into, which in theory should accept them without deflecting the blades if the Mini is stored "properly" according to DJI's diagram. That should work beauty fine.

However...

In order to actually fit the rear blades into that trough, the blades first need to be nested together (crossed over each other) laterally across the body of the Mini. When folded together, the blades from one side must bend to fit under the blades of the other side. When stored according to DJI's diagram, the left-rear blades are again bent against the underside of the Mini, exactly as far as they are in the previous image above where the weight of the Mini was resting on them.

This image below shows how far the left-rear blades must bend in order to fit nested under the right-rear blades. Blade-1 is standing undeflected. Blade-2 is being bent down to force it under the opposite side's blades. Note it is already touching the body of the Mini. To fit both blade-1 and blade-2 under the opposite side's blades requires pressing them against the body of the Mini.

Yes, the tips of the (un-numbered) right-rear blades will droop nicely unimpeded into the trough designed for them in the Fly More case. But the left-rear blades are again being bent exactly as if the full weight of the Mini was resting on them. Is this not equally detrimental?

View attachment 115373



If your props are only lightly pressing against each other, I suggest that they're already permanently bent as new straight blades cannot be positioned like this without forcing them to bend.


And yet you have no problem seeing how similarly bent props (due to incorrect storage) would be more likely to trigger this condition?

Thanks @Zbip57 - apologies, I should have referenced you in my post #242.

 

[Thomas B]

I believe this thread is supposed to be about uncommanded descent.

 

[FoxhallGH]

I believe this thread is supposed to be about uncommanded descent.

It is, and we are discussing what we strongly believe to be the cause of that problem i.e. the DJI suggested method of storage of the folded up Mavic Mini leads to propellor blade distortion, loss of blade pitch and lift, and that leads to uncommanded descents of the Mavic Mini when max power is needed.

 

[Zbip57]

Thanks @Zbip57 - apologies, I should have referenced you in my post #242.

No worries.

I believe this thread is supposed to be about uncommanded descent.

Yes it is.

And more precisely, this lengthy thread has evolved into an attempt to explain the root cause of uncommanded descents. More and more evidence points to propeller blade deformation as the cause, ultimately prompting DJI to introduce new Motor Speed Error and Propeller Speed Error warnings in the latest firmware update with explicit instructions to replace the propeller blades on the affected motors.

The question remains, what is causing this propeller deformation?

Because of the canted mounting angle of the rear motors, the rear propeller blades cannot be nested together when crossed laterally across the Mini's body without forcing one side or the other to bend under the opposite side.

As shown in this image, blade-#1 and #2 must be bent down in a curve to fit under the opposite side's blades. This results in blade deformation due to two influences.

One: The blade eventually takes on a permanent drooped curved shape due to the bending moment imposed on the blade's tip.

Two: When the blade tip is pressed down like this, the blade's trailing edge near the root of the blade contacts the body of the Mini. The tip is pressed down while the trailing edge is pressed up. This creates a torsional rotation along the entire length of the blade causing it to twist, flattening its profile and reducing its angle of attack.



When the prop blades are stored like this for a length of time, these two forces (bending & twisting) combine to permanently reduce the lift efficiency of the blades. The flight controller attempts to compensate for this reduced lift by increasing the motor speed. A sufficiently elevated motor speed will eventually reach the threshold value set by DJI to trigger their new Motor Speed Error warning message. When that happens you are instructed to replace the affected propeller blades.

New blades will cure the issue, unless of course you continue to again store your Mini with the blades crossed like this.

Prior to firmware v01.00.0500 there were similar warning messages about Max Power Reached. This was routinely ignored. Subsequent to firmware v01.00.0500 people are still ignoring the Motor Speed or Propeller Speed warnings. Or they take a cursory glance at the propeller blades and declare, "if there is any bending at all, it's barely noticeable." Seeing nothing visibly wrong with the blades, they insist the Speed warnings must be a defective firmware glitch, or that DJI's detection threshold must be set too sensitive, and they happily continue flying.

Eventually we come to the Uncommanded Descent. The Mavic Mini motors can spin only so fast. If the propeller's lift profile degrades sufficiently to the point where the motor is incapable of turning any faster, then it cannot produce the required lift to sustain flight and the Mini sags to the ground.