Propeller blade deformation, causing a reduction in lift capacity, prompts the flight controller to spin the motors faster to continue generating the required lift to sustain flight.  Eventually the motor speeds will hit a preset threshold limit that, ever since the latest firmware  v01.00.0500, triggers a Motor Speed Error or Propeller Speed warning with an accompanying instruction to replace the propeller blades on the affected motor, as identified by the beeping ESC.

If these warnings are ignored, and the blade performance degrades even further, you ultimately risk experiencing the dreaded "uncommanded descent" where the Mini is no longer capable of generating sufficient motor speed to remain in flight.


The big question is, what is causing the degradation in propeller performance?  What is making the blades bend so that they lose lift?  Why are even brand new Minis sometimes reporting these same error messages?  Why are people repeatedly receiving the same warnings even after installing new blades?  Why is it almost always the same left-rear motor?

The reason is because of the way the propeller blades are stored when the arms are folded and the blades are crossed over/under each other if the blades are nested laterally across the Mini's body.

The root problem is that the motors are mounted at an angle.  The rear motors are canted outboard.  When the arms are folded and the rear props are nested across the body, the blades must bend to fit under each other.

Man, it's frustratingly difficult to post images in this DJI forum...

Over on the MavicPilots forum, I got into a discussion concerning propeller holders designed to keep propeller blades from flopping around in order to ensure they stay "properly" stored in the Fly More case.  My point was that storing the blades crossed is what's causing the blades to bend, regardless of which case is being used, and especially if propeller holders are being used to force the blades into the crossed position.


Rather than try to re-type everything here, please read what I've posted in this thread over on the MavicPilots forum.  Read that and you will understand how the blades are being bent.
mavicpilots.com/threads/propeller-guards.99882/

Note, you do not need to register or login to that forum to read the posts.  However, the images are only displayed in small thumbnail format unless you're logged in.  You will want to see the images in full size.

Please have a look at what is posted there, then come back and discuss here if you like.

Is this image showing now???  (Why is there no editing preview available in this forum software?)

If the image is showing, here you can see how straight new (un-bent) rear propeller cross because of the way the rear motors are canted outboard.

If the blades must be folded together like this to fit into the Fly More case, or they are forced to stay together when using propeller holders, it is clear that the tips of the blades are bent down in order to fit underneath the other side's blades.

It is important to note that this is not only curving the blades down.  It is also twisting the blades.  See how the tip is bending down, while the trailing edge near the root of the blade has contacted the body of the Mini?  So the tip is being pushed down while the trailing edge is being pushed up.  That twists the blade.

It is this torsional twisting that flattens the blade's profile, reducing the propeller's lifting capacity.

Of course if the blades are jammed into the case "improperly" with the weight of the Mini resting on them, or if the Mini is placed onto a tabletop with the blades crossed underneath, that will also bend the blades.

But the thing you need to notice is that merely crossing the blades laterally across the Mini's body, folded over/under each other, is already enough to cause the blades to deform.

I always prefer to remove my blades before putting them into the bag to avoid similar issues.

Zbip57 Posted at 10-23 09:00
If the blades must be folded together like this to fit into the Fly More case, or they are forced to stay together when using propeller holders, it is clear that the tips of the blades are bent down in order to fit underneath the other side's blades.

It is important to note that this is not only curving the blades down.  It is also twisting the blades.  See how the tip is bending down, while the trailing edge near the root of the blade has contacted the body of the Mini?  So the tip is being pushed down while the trailing edge is being pushed up.  That twists the blade.

Hello  Zbip57, thank you for reaching out and sharing your experience about the Mavic Mini. This is indeed a great help and tips to everybody. I appreciate your effort in posting your insight about this error here in the forum. Thank you for your support.

So why is almost always the rear blades that get bent and trigger Motor Speed Errors, and why hardly ever the front blades?

Because, when the arms are folded, the front motors sit nearly level with each other.  Their blades will nest together across the body without bending the blades.

If the tips of your rear blades do not look like mine, with the their tips crossed, but yours nest easily together with blades lying flat and parallel to each other, it's because your blades are already permanently deformed.


Your Mini may still fly perfectly well, and you may never (yet) have received a Motor Speed Error warning.  That's great.  Your blades are probably still okay.

But if you have received a Motor Speed Error, or a Propeller Speed Error, it means your motor has reached a dangerous rpm level sufficient to trigger the threshold value to prompt the Speed warning.  You really need to check your props, as prompted by the warning.

If you see nothing wrong with your props and think the warrning messages are erroneous (or even due to defective firmware), there is a simple hover test whereby you can measure your propellers' lift efficiency.

See the post I linked above, and these three further posts over on the MavicPilots forum for full details.

Why are Props bending - mavicpilots.com/threads/motor-speed-error-mavic-mini.86130/page-13#post-1038101
The Hover Test - mavicpilots.com/threads/motor-speed-error-mavic-mini.86130/page-13#post-1038918
Proper Storage - mavicpilots.com/threads/motor-speed-error-mavic-mini.86130/page-14#post-1042991


If anyone has questions, I'm happy to discuss here.

Suren Posted at 10-23 09:02
I always prefer to remove my blades before putting them into the bag to avoid similar issues.

Yes, that works great on the Mini's big brothers which all have quick release prop mounts.  But the Mavic Mini's propeller blades are screwed down with tiny screws secured by blue Loctite.

There is a very real risk of damaging the screw threads if they are undone repeatedly.  At the very least, once fastened, the loctite should not be disturbed as it prevents the screws from vibrating loose.  It would be instantly catastrophic if a blade was lost in flight.

DJI Paladin Posted at 10-23 09:06
Hello  Zbip57, thank you for reaching out and sharing your experience about the Mavic Mini. This is indeed a great help and tips to everybody. I appreciate your effort in posting your insight about this error here in the forum. Thank you for your support.

Thanks, Paladin.

This is a serious problem that needs to be acknowledged by DJI.  Too many people are affected by this.

Furthermore, there is far too much misinformation being broadcast about these Motor Speed Error and Propeller Speed warnings.  People insist it's only being caused by improper storage in the Fly More Combo case.  Sure, that obviously would be even worse for the props.

But people seem to be completely unaware that even proper storage in the Fly More case will bend and deform the prop blades.  That is because the Fly More case is designed to store the props in the folded and crossed position.  It is not possible to cross new straight rear blades like this without forcing them to bend.


The proof is that even people with standard Minis (not Fly More Combo) have also reported Motor Speed Errors with brand new Minis straight out of the box.  Standard Minis are also packed and shipped with their arms folded and props crossed laterally across the Mini's body.

Zbip57 Posted at 10-23 09:29
Yes, that works great on the Mini's big brothers which all have quick release prop mounts.  But the Mavic Mini's propeller blades are screwed down with tiny screws secured by blue Loctite.

There is a very real risk of damaging the screw threads if they are undone repeatedly.  At the very least, once fastened, the loctite should not be disturbed as it prevents the screws from vibrating loose.  It would be instantly catastrophic if a blade was lost in flight.

Ahhh, it is a mini. I really need to start paying attention as to what types of drones are mentioned

I believe you are correct, I have a case not the Fly more combo, and have been using it without any prop guards and haven't had this problem. Also I recall a person who had just received a fly more combo and had this issue!

So how to avoid bending your props?

Ever since replacing my blades back in April 2020, I've been storing my Mini on a shelf with the arms open.  I've never had a problem again.

Storing the Mini with arms folded but props positioned longitudinally alongside the body, rather than crossed laterally over/under the body, that will not bend the blades.

If you look at any of the User Manuals or Quick Start Guides for the Mini, there is not a single diagram anywhere showing the props folded across the body of the Mini.  All of the images show the blades positioned longitudinally when the arms are folded.  Even the little animation on DJI's website shows the Mini folding its arms and ending with the propeller blades positioned longitudinally, not crossed.

Storing the Mini with the props folded together laterally across the body, regardless of which case or which prop holders are used, is what's causing the blades to bend.


If I'm not just storing my Mini with arms unfolded on a shelf, but need to transport it during travel, I use a different type of carrying case which allows the props to be positioned longitudinally.  Like this one:

Excellent tips - thanks for sharing

For those of you who, for whatever reason, choose not to follow the links to my other posts on the MavicPilots forum, here are some sample hover test Motor Speed plots.

This graph shows my Motor Speeds during a two-minute hands-free hover test.  All of the propeller blades were replaced with fresh new straight blades, except the right-front which are still the original blades.  Note that all four motors are turning at relatively equal speed of about 9600 rpm.

This graph was posted by someone else before replacing any blades.  


Note how consistently the left-rear motor (blue) is turning at a significantly higher rpm in order to produce the lift required for hover.  The other counter-clockwise turning motor, the right-front (red), consequently also spins faster.  In fact all four motors are turning much faster than the 9600 rpm of my motors with fresh blades.

Here are two more.  These were each just short one-minute hover tests to compare motor speeds with/without prop guards (cages) installed.

The first one is without prop guards.  I extracted the CSV file so I could load it into Excel to calculate the average motor speeds.  The calculation excluded any rpm values less than 8000 rpm to trim out the takeoff and landing segments.  I really should have trimmed out the entire first 30 seconds, as you can see it took about the long for the Mini to settle into a stabilized hover.  Nonetheless, you can see a hover speed at an average of approximately 9600 rpm is reasonable.

If you are worried about performing a hover test indoors, it is safer to do it with the DJI prop guards (cages) installed.

Here is a second one-minute hover test, this time with the prop guards installed.  The graph is very similar, but the added weight and aero drag of the cages requires the motors to spin approximately 1000rpm faster.

Note again, that it takes the Mini about 30 seconds to acquire a stable hover.  It's better to let it sit there in hover for two to five minutes to get an accurate assessment.

In any case, you want to see all four motors turning at nearly equal speeds.  If any of your motors is turning at a significantly higher speed than the others, that's a sure sign that the blades on that motor are under-performing.

Zbip57 Posted at 10-23 15:10
This graph was posted by someone else before replacing any blades.  

Is there any chance that the user was at a higher base altitude than you? The delta between all motors looks to be about +-1000 rpm. I thought that was considered acceptable.

GaryDoug Posted at 10-23 19:45
Is there any chance that the user was at a higher base altitude than you? The delta between all motors looks to be about +-1000 rpm. I thought that was considered acceptable.

If he was doing the hover test at a higher altitude compared to my tests (i.e. in thinner air), then yes the motors would need to work harder, spin faster, to generate the same amount of lift to hold a steady hover.

However, all four motors should still be spinning at near equal speeds.  There shouldn't be any significant difference between the motor speeds.

In a stable hover, all four motors will spin at the same speed.  If they're not, it means the propeller blades are not in equal shape.

"In a stable hover, all four motors will spin at the same speed.  If  they're not, it means the propeller blades are not in equal shape."

I should point out that it's important to do these hover tests indoors in order to minimize the influence of wind.  If you do choose to do the test outdoors, make sure to do it under calm conditions in a sheltered location.  If the Mini is leaning into the wind to hold itself in a steady hovering location, the motors will run at different speeds in order to hold that tilted attitude.

For example, here is a test to show what the motor speeds do when given full forward or full backward stick input.  This was done outdoors on a day with a bit of tailwind blowing at the same time from the left rear.  Note at the portions of the graph marked "Hover" how much slower the rear motors are turning compared to the front.  The left-rear (blue) is turning significantly slower in hover as the Mini holds that corner down to lean back into the tailwind.

At full forward stick input, both the rear motors speed up as the front motors slow down to pitch the Mini nose down.  With full rearward stick input the rears slow and the front motors run fastest to pitch the Mini nose high.

This shows how much the stick input does affect the motor speeds.  But wind also affects the Motor Speed plots as the Mini has to adjust its attitude to hold position.  That's why the Hover Test really should be done hands-free and indoors (with no wind) in order to get a meaningful reading of the motor speeds.  If you must do the test outdoors, then you should have the Mini hover steady for a couple of minutes, then yaw 90° and hold for another couple of minutes, yaw another 90°, etc.  Then the effect of the wind (if any) should show up clearly on your data traces.

Here is a similar test on the same day with full left and full right stick inputs.  The Mini was pointing in the same direction the whole time, with a slight tailwind from the rear left.  You can see the same things happening here with the motors on the high side running at increased speed.

If we are going to prove, or disprove, this theory of how prop blades are being bent and damaged, we need lots of people to post their own hover test Motor Speed plots for comparison.

There's no denying that people are continuing to report Motor Speed or Propeller Speed errors. People are getting tired of being told to replace their propeller blades. I'm convinced this explanation of how the props are being bent makes sense.

If you are still skeptical, or see nothing at all wrong with your props, and you are convinced your blades are fine, the Hover Test is the simplest way to accurately measure the performance of your propeller blades. Knowing whether or not they are functioning at their best will give you confidence in deciding whether to continue flying, or not.

If enough evidence can be collected to prove the cause of this problem, maybe DJI will acknowledge the issue and step up with a proper solution.

If you don't know how to get or post your Motor Speed plots, I'm happy to help.

Here's an explanation of where to find the DAT log file containing motor speeds, and how to use CsvView to plot the graph.

mavicpilots.com/threads/motor-speed-error-mavic-mini.86130/page-15#post-1121175

Jumping on this thead as I also saw your comment on your Youtube and you have checked out my thread as well. My mini is like 25 days old and has this issue for which I changed Rear props on both sides and right front prop with brand new ones. No storage nothing. I receive the propellers, I change all and I fly directly without changing anything and I still have the same issue. Here's a hover test indoors: . The Rear left is always like 1.5-2k RPM faster.

I am unsure of what to do. Either I should ignore it or there is an issue with the drone itself and not the props.

fans2825b6e8 Posted at 11-20 03:58
Jumping on this thead as I also saw your comment on your Youtube and you have checked out my thread as well. My mini is like 25 days old and has this issue for which I changed Rear props on both sides and right front prop with brand new ones. No storage nothing. I receive the propellers, I change all and I fly directly without changing anything and I still have the same issue. Here's a hover test indoors: [view_image] . The Rear left is always like 1.5-2k RPM faster.

I am unsure of what to do. Either I should ignore it or there is an issue with the drone itself and not the props.

What provoked you to do these tests? Were you having issues, warning prompts or just curiosity?

If you've never had an issue and did this only for data, nothing looks out of the ordinary, was the hover test done indoors or out? You are in safe operating RPM range, while the left Rear is still higher unless it's causing you some kind of issues, you are safe to fly.  

fans2825b6e8 Posted at 11-20 03:58
Jumping on this thead as I also saw your comment on your Youtube and you have checked out my thread as well. My mini is like 25 days old and has this issue for which I changed Rear props on both sides and right front prop with brand new ones. No storage nothing. I receive the propellers, I change all and I fly directly without changing anything and I still have the same issue. Here's a hover test indoors: [view_image] . The Rear left is always like 1.5-2k RPM faster.

I am unsure of what to do. Either I should ignore it or there is an issue with the drone itself and not the props.

The Mini is symmetric, evenly balanced, with counter-rotating propellers.  If anything, it's only very slightly nose-heavy.  In a stable hover there is no physical reason for one particular motor to be spinning consistently faster than the others.


If the props are all in equally good shape, they should all be spinning at near equal speed when in a steady hover, unless the Mini is working to hold position against wind.

Try repeating the test in the same location, but with the Mini pointing in different directions.  That would show whether a crosswind is influencing the results.

Otherwise, try swapping the blades from the left rear motor with any of the other motors to see if the higher motor speed follows that particular set of blades.

The difference shown in your graph is not large, but it is a consistent clear difference.  I'm curious what's causing that.

Also, let the hover test run for a longer time.  I see yours was only about 30 seconds long.  

Check my graph in post #19 above.  It takes roughly 30 seconds for the Mini to settle into a stable hover before the motor speeds equalize.

If you are correct (and I believe so), should not be a matter of DJI start a recall of all MINI's case to replace for a new one that stores the mini in the correct way to avoid issues on propellers?
Esta seria a maneira mais barata para termos essa solução. Otherwise, as it seems also to be a disign problem, then DJI should do a recall of all the Mini drones to replace the back motors' arms for new ones designed to be folded in the correct angle to avoid this issue.

Considering that this is DJI, I do not believe they have the policy to carry out these recalls (or hopefully I can be wrong), but here is a tip in respect to consumers. When this kind of situation occurs with car manufacturers, they are required by law to make these recalls (at least in my country we have strict laws for car manufacturers when this happens). And no additional costs for consumers.

Zed_Br Posted at 11-20 08:39
If you are correct (and I believe so), should not be a matter of DJI start a recall of all MINI's case to replace for a new one that stores the mini in the correct way to avoid issues on propellers?
Esta seria a maneira mais barata para termos essa solução. Otherwise, as it seems also to be a disign problem, then DJI should do a recall of all the Mini drones to replace the back motors' arms for new ones designed to be folded in the correct angle to avoid this issue.

"If you are correct (and I believe so), ..."

I am convinced that I'm correct.  I'd be happy to change my mind if anyone can conclusively demonstrate and prove that folding the blades across the body does NOT result in blade deformation.

"... should not be a matter of DJI start a recall of all MINI's case to  replace for a new one that stores the mini in the correct way to avoid  issues on propellers?"

That would certainly be nice, but I doubt DJI will ever admit to being at fault here.  ALL of the original Mini's were shipped from the factory with the arms folded and blades crossed, even standard non-Fly More Mini's.

For me, the solution is to never store the Mini with the props folded together.  I leave mine sitting on a shelf with arms open.  If I need to transport my Mini, I use a case which allows storing the Mini with the props positioned longitudinally along the sides of the Mini, not crossed laterally across the Mini's body.

Zed_Br Posted at 11-20 08:39
If you are correct (and I believe so), should not be a matter of DJI start a recall of all MINI's case to replace for a new one that stores the mini in the correct way to avoid issues on propellers?
Esta seria a maneira mais barata para termos essa solução. Otherwise, as it seems also to be a disign problem, then DJI should do a recall of all the Mini drones to replace the back motors' arms for new ones designed to be folded in the correct angle to avoid this issue.

"Otherwise, as it seems also to be a design problem, then DJI should do a  recall of all the Mini drones to replace the back motors' arms for new  ones designed to be folded in the correct angle to avoid this issue."

That is unlikely to happen.  I don't know why the motors are mounted at an angle like they are.  But I'm sure there is a very good reason for it, stability vs. responsiveness in flight.

I'm curious to know whether the motors on the new Mini-2 are still mounted at the same angles?  Clearly they are no longer shipped with the rear propeller blades crossed.  The new Mini-2 has a propeller holder that positions the rear blades at an angle of about 45°, so the tips are barely touching each other, NOT crossed.

ABeardedItalian Posted at 11-20 04:24
What provoked you to do these tests? Were you having issues, warning prompts or just curiosity?

If you've never had an issue and did this only for data, nothing looks out of the ordinary, was the hover test done indoors or out? You are in safe operating RPM range, while the left Rear is still higher unless it's causing you some kind of issues, you are safe to fly.

I had a motor spinning too fast error immediately after launch in a very stable weather near my home. The Lback was showing indicator. I turned it off and turned it on again and it never happened but these tests are a result of it.

The graphic I showed is during an indoor hover. With fresh sets of propellers out of the box and the result is still same. I am aware that these RPMs are safe for flying in regular conditions and I would not worry if this was a 2 year old drone but its a brand new drone with brand new props. I am just wondering if I am flying in hard conditions, will the weather or wind resistance be effected because of this.

About the longer hover test, I can do it but don't think it will change anything. I have flown multiple times since I noticed for longer periods as well and this thing is always constant before and after changing props. Here is a regular flight: https://i.imgur.com/pIlOVJt.png

CC: @Zbip57

fans2825b6e8 Posted at 11-20 19:55
I had a motor spinning too fast error immediately after launch in a very stable weather near my home. The Lback was showing indicator. I turned it off and turned it on again and it never happened but these tests are a result of it.

The graphic I showed is during an indoor hover. With fresh sets of propellers out of the box and the result is still same. I am aware that these RPMs are safe for flying in regular conditions and I would not worry if this was a 2 year old drone but its a brand new drone with brand new props. I am just wondering if I am flying in hard conditions, will the weather or wind resistance be effected because of this.

All I can say is, that's not what I'm seeing with my Mini.  In hover, my motors all turn at the same speed.

Humour me.  Do another hover test, hands-free at least two minutes, then yaw 90° to the right, hover hands-free another two minutes, yaw a further 90° right, etc.

This way you'll have one flight with the Mini pointing North, East, South, West, hovering for at least 2 minutes at each compass point.  Then plot the Motor Speeds from that one flight.

That should ensure that any possible wind interference is accounted for.  If your left-rear is still spinning consistenly faster than the other motors at each compass direction, that would indicate a problem with the blades on that motor.  I don't see how it could mean anything but that.

Wow...
What a great post @Zbip57 .

Been looking to find why this happenes through other forum post to prevent it from happening again but without luck, and I couldn't see that my blade was sligthly bended after finding your great post, and the problem is most def the (fm)case holder. I'm gonna call DJI on Monday and make them send me new propellers and a functional case as there is no warning about this in the manual, and you can clearly see it's a design flaw when unboxing a new product having them crossed . Probably nothing they will admit, as this can trigger a mass law suit, and recall of products.

I'm thinking of buying the Mavic Mini 2, as the drone without this issue is awasome.
Anybody know if this design flaw still exist in the fly more case?           

xxxxxxxxxxxx

Zbip57 Posted at 2020-11-20 09:50
"If you are correct (and I believe so), ..."

I am convinced that I'm correct.  I'd be happy to change my mind if anyone can conclusively demonstrate and prove that folding the blades across the body does NOT result in blade deformation.

Thanks @Zbip57 !
I had my MIni since November 2019 and had the first error in Janurary 2021, after having the Mini for more than 6 weeks in the Fly More Case.
Before that, the drone never was in the case more than  a few days. So it's 100% a wrong storage, which causes this.


Greetings from Germany
Uwe

Artellic Posted at 2-20 04:56
Wow...
What a great post @Zbip57 .

i never used the original case for my Mini`s.

PGYtech has a small case wich is great to use, did modify the part for the mini2 ; piece of 'distance foam' for the front of the mini,so blades on the bottom don`t touch the case.

cheers
JJB

Artellic wrote, "Anybody know if this design flaw still exist in the fly more case?"

Mine is the original Fly More case with a raised hump in the bottom to support the belly of the Mini.  The rear props, folded laterally underneath the Mini, are supposed to hang freely into the cavity in the bottom of the case in such a way that there is no pressure on them.  However, as described above, simply folding the blades laterally across the body is what is causing the blades to bend, even if they don't touch the bottom of the case.

The original Fly More case has a raised portion to lift the belly of the Mini (Orange rectangle).  The label in the bottom of the case says to fold the blades laterally (left under right) so they droop into the cavity (Red oval).  With the arms folded, the Mini's feet (Red rectangles) fit into the other cavity.  Obviously if you improperly position the blades onto the raised portion (Orange rectangle), they will bend when the weight of the Mini rests on them.  However, as described in my previous posts above, simply folding the blades laterally across the body is what is causing the blades to bend, even when "properly" positioned into the cavity without touching the bottom of the case.



Apparently there is a 2nd generation version of the Fly More case.  The label has been revised to show the blades now crossed the other way (right under left).  That doesn't change anything, as the prop bending is still being caused by folding the blades laterally.  But in this configuration it will now most likely be the right-rear blades that first trigger the Motor Speed warning.


Furthermore, the raised portion has been removed from the bottom of the case.  There no longer is any support for the belly of the Mini, other than a very small hump between the folded feet.  This means the bottom of the case in now FLAT, with the full weight of the Mini resting onto the laterally folded prop blades.  That's crazy.  If stored with the blades crossed as shown on the label, this pretty much guarantees the blades will be bent!



What is DJI thinking here?

Here are mine hover results:



Not sure if I should change the props or not. I don't get any warnings during the flight.