Propeller Guards

[Zbip57]

That DJI website animation shows the Mini always stored vertically in that dome with props hanging loosely pulled downward by gravity while Minis in cases are aligned horizontally in case with gravity pulling blades down horizontally during storage,

The relevant difference here is that with the Mini stored vertically in the dome the props are hanging loosely alongside the Mini's body, not bent to slide under each other positioned across the body of the Mini as they are in most storage cases.

It's not the gravity that's causing the blades to bend. Think about it. The blades are strong enough to support the full weight of the Mini in flight. The tiny weight of the blades themselves is not sufficient to cause them to droop and bend down due to gravity alone when stored horizontally.

I've been storing my Mini ever since on a shelf with arms unfolded with the blades not crossed. No problems whatsoever.

 

[Zbip57]

To summarize, the rear motors of the Mini are mounted at an angle canted outwards. You can clearly see this when new straight prop blades are installed. New blades cannot be nested under each other when folded laterally across the body without forcing one side or the other to bend under the opposite side's blades.





To nest the rear blades folded together, the blades on one side must be bent down. See blade #1 undeflected, versus blade #2 forced down to fit under the opposite side's blades.



The blades are quite flexible and will not resist being forced into this position. They do spring back to resume their correct shape. However, if left stored in this position for any length of time the blades will eventually remain deformed like this.

The important thing to note about this is that not only will the blade take on this permanent drooped shape, it also affects the blade's angle of attack profile. The blade is flattened, producing less lift. The flight controller compensates for this by spinning the motors faster. Eventually the motor rpm reaches a threshold value sufficient to trigger the Motor Speed Error, or Propeller Speed Error message. If you ignore that long enough, or the propellers are sufficiently mishapen, the motors might reach their peak rpm capacity and, unable to spin any faster, cannot produce enough lift to sustain flight.

If you are still skeptical, or think the bend in these blades is "barely noticeable", don't take my word for it. Don't just take a cursory glance at your props and see nothing wrong with them. Do your own simple hover tests and plot the motor speeds. Compare your motor speeds using your worn bent props versus a set of brand new props. Then you'll know for sure.

But, if you install fresh new blades and then right away continue storing the Mini with the blades folded and bent across the body, it won't be long before you again start seeing the same Motor Speed Error warnings...

 

[Pawpaw Woody]

@ pawpaw - do you mean prop protectors when stored? Or prop guards when flying? I too am interested in the best prop protectors for storage that fit in the flymore case.

Yes Prop protectors/guards when mini is folded and in the DJI case!

 

[Pawpaw Woody]

Take the props off and problem solved

Then you would have to replace hold down screws every flight

 

[Pawpaw Woody]

To summarize, the rear motors of the Mini are mounted at an angle canted outwards. You can clearly see this when new straight prop blades are installed. New blades cannot be nested under each other when folded laterally across the body without forcing one side or the other to bend under the opposite side's blades.

View attachment 115285

View attachment 115286

To nest the rear blades folded together, the blades on one side must be bent down. See blade #1 undeflected, versus blade #2 forced down to fit under the opposite side's blades.

View attachment 115287

The blades are quite flexible and will not resist being forced into this position. They do spring back to resume their correct shape. However, if left stored in this position for any length of time the blades will eventually remain deformed like this.

The important thing to note about this is that not only will the blade take on this permanent drooped shape, it also affects the blade's angle of attack profile. The blade is flattened, producing less lift. The flight controller compensates for this by spinning the motors faster. Eventually the motor rpm reaches a threshold value sufficient to trigger the Motor Speed Error, or Propeller Speed Error message. If you ignore that long enough, or the propellers are sufficiently mishapen, the motors might reach their peak rpm capacity and, unable to spin any faster, cannot produce enough lift to sustain flight.

If you are still skeptical, or think the bend in these blades is "barely noticeable", don't take my word for it. Don't just take a cursory glance at your props and see nothing wrong with them. Do your own simple hover tests and plot the motor speeds. Compare your motor speeds using your worn bent props versus a set of brand new props. Then you'll know for sure.

But, if you install fresh new blades and then right away continue storing the Mini with the blades folded and bent across the body, it won't be long before you again start seeing the same Motor Speed Error warnings...

It would appear that DJI ships these with the paper sleeve that holds the blades in alignment without
applying pressure for this exact reason. Perhaps a reusable designed prop alignment sleeve would be the best answer. Very informative discussions and thanks for the tips and ideas. I think I will forgo
the aftermarket products at this time!

 

[Zbip57]

It would appear that DJI ships these with the paper sleeve that holds the blades in alignment without
applying pressure for this exact reason.

But holding the blades nested laterally in the crossed position is what's applying the pressure, regardless of whether it's DJI's original paper sleeve or any one of the various aftermarket propeller holder products used to hold the props in that position.

See this post and the one immediately following it:
mavicpilots.com/threads/mavic-mini-uncommanded-descent-tests.86237/page-13#post-1123386

 

[Pawpaw Woody]

Any reason not to use the DJI-manufactured prop guards?

My bad- I was referring to the propeller storage guards/holder that keep prop aligned while folded up and stored in the DJI case

 

[Pawpaw Woody]

But holding the blades nested laterally in the crossed position is what's applying the pressure, regardless of whether it's DJI's original paper sleeve or any one of the various aftermarket propeller holder products used to hold the props in that position.

See this post and the one immediately following it:
mavicpilots.com/threads/mavic-mini-uncommanded-descent-tests.86237/page-13#post-1123386

Would that not mean that any MM's stored on a shelf or inventory before sale would have prop deformation even before the first flight? After reading the tips and comments I did a closer observation of the props and how they are seated
and found that 2 mounting screws were loose and needed retightening (yes original factory installation) and also that 3 props had a significant amount of play (up and down )at the hub... The remaining all were closely fitted to the mount
points. Are the hub tolerances different on some blades due to manufacturing or possibly mounting screw length tolerances. I am now thinking about the centrifugal forces applied on the props while spun up? Are they so thin and flexible that they flatten out slightly during flight? Very interesting discussions from what I thought would be a simple answer to my original question!

 

[Zbip57]

Would that not mean that any MM's stored on a shelf or inventory before sale would have prop deformation even before the first flight?

Yes! Search the forums. There are many reports of people receiving Motor Speed Error or Propeller Speed Error warning messages, with instructions to replace propeller blades, even on their brand new Minis straight out of the box.

There are many more posts from people (like myself) who've been flying theirs with no apparent problem only to receive those error messages on the first flight after upgrading to the latest firmware v01.00.0500. Previous firmware versions had only "Max Power Reached" warnings. DJI now made the warnings more explicit.

Look at these photos (not mine). This is how standard Minis are boxed and shipped (similar to the Fly More Combo Minis). The Mini sits in a plastic tray with arms folded and props crossed laterally across the Mini's body. There is a trough below for the rear blades to hang into. Like all Minis, there is a paper band around the prop blades to ensure they remain "properly" positioned and don't flop around.









The guy who originally posted these photos was more concerned about the gimbal cover being loose, and he was asking if this was normal? But look at the condition of the prop blades. The right-rear blades are free to hang down into the trough designed for this purpose in the shipping box. But the tips of the left-rear blades are not free. They're bent down.

Here's an even more extreme example. This guy hadn't even removed the shipping labels off his Mini yet. This is straight out of the box. Check the left-rear!


Back to the photo I posted previously... It's important to realize that the blades are not only being bent curved down. You can see in this photo that, as the tip is bent down, the trailing edge near the root of the blade contacts the body of the Mini. Tip pushed down, trailing edge pushed up, this forces a torsional rotational in the blade. The blade is not only being curved, it is also being twisted. This twist flattens and reduces the blade's angle of attack, reducing its ability to generate lift.



Sure, the blades are springy and might bounce back. But if stored for some length of time with the blades forced into this position, the deformation eventually becomes permanent.

Every one of the aftermarket "blade holders", as well as DJI's original paper bands, are intended to retain the blades securely in the crossed position so they don't flop around and remain sitting "properly" in the trough designed for them in the carrying case.

But this crossed position is what is causing the blades to bend. And, since they're always shipped with the left-rear blades folded under the right-rear blades (per the diagram in the bottom of the Fly More Case), this is why it is almost always the left-rear motor that first triggers a Motor Speed Error.

 

[Carlos56]

I saw the left rear motor speed warning after a few weeks of owning the MM. I had been storing it in the DJI Flymore case. I hadn't been particularly careful about placing the props underneath the drone when placing it in the case. Not sure if it was from overlapping them, or pinching them between the body and the case.

I now store the drone on a shelf, and only place it in the case for transportation to the launch location, and I am careful about not crossing the props. I have one side point SLIGHTLY forwards, just enough so they don't overlap, but are still in the open area of the case. I've had no problems since doing this.

I think the issue is made more likely if you store for a long period, or if you store in warm conditions where the blades will be softer and more easily deformed. If they are crossed or pinched for a long time they will take on that deformation. If they are crossed or pinched and then warmed up and cooled in that position, they will deform and set in the flattened shape.

So my recommendation is to minimize time stored in the case, and try to avoid any time in the case when ambient temperatures are high.

Interesting note: When I had the motor speed warning on the left rear rotor, my MM would take off crooked. It rolled to the left immediately on leaving the ground before self correcting. Obviously on take off, both left and right rear motors are running at the same speed, and the control software corrects when the MM rolls to the left by speeding up the left rear motor to compensate.

Anyway this roll on take off is a good way to check if you have deformation of the props (at least when one side is much worse than the other). It is easier than digging into DAT files for prop speed data.

 

[TruGreen]

i use these that i got off ebay from china. they fit within the fly more case but are a bit snug for the bottom one, but it does fit the case

Mavic Mini Prop Holders and Protectors

I found these on the good ole' Ebay. Shipping from Hong Kong took a few weeks. Must say I'm impressed though. They are 3D printed, but fully cover the motors and props. Perfect for pocket carry so they blades don't snag. Mini does fit inside the Fly More case, but it a tad snug. So when removing...

mavicpilots.com

 

[Zbip57]

i use these that i got off ebay from china. they fit within the fly more case but are a bit snug for the bottom one, but it does fit the case

Over all I'm happy with these and they deff will protect the blades better than them flopping around.

You've entirely missed the point.

Pros & Cons of these prop holders:

Pro:

1. They stop the blades from flopping around when carrying the Mini around loose. Okay, I get that.

Cons:

1. They force the rear blades into the worst position most likely to bend the blades.
2. Bending is now even worse because you've reduced the available space in the Fly More Case's trough.
3. You spent money on this.

 

[Pawpaw Woody]

You've entirely missed the point.

Pros & Cons of these prop holders:

Pro:

1. They stop the blades from flopping around when carrying the Mini around loose. Okay, I get that.

Cons:

1. They force the rear blades into the worst position most likely to bend the blades.
2. Bending is now even worse because you've reduced the available space in the Fly More Case's trough.
3. You spent money on this.

In all fairness I did ask if there were prop holders/guards that people can recommend. Thanks for all responses to this post!

 

[Zbip57]

In all fairness I did ask if there were prop holders/guards that people can recommend. Thanks for all responses to this post!

Fair enough.

But if you feel the need for prop holders, find some that do not bend the blades crossed over/under each other.

 

[Pawpaw Woody]

Fair enough.

But if you feel the need for prop holders, find some that do not bend the blades crossed over/under each other.

I agree! I guess the law of unintended consequence is at work here as I had no idea this was
even a concern until posting the question... I’m glad that I have been educated on the subject now and can make an informed decision! “If Any"

 

[TruGreen]

You've entirely missed the point.

Pros & Cons of these prop holders:

Pro:

1. They stop the blades from flopping around when carrying the Mini around loose. Okay, I get that.

Cons:

1. They force the rear blades into the worst position most likely to bend the blades.
2. Bending is now even worse because you've reduced the available space in the Fly More Case's trough.
3. You spent money on this.

My blades don't push down. They simply cross cross. Have had no negative effects as of yet. Since owned and been using

 

[LotusFan]

My blades don't push down. They simply cross cross. Have had no negative effects as of yet. Since owned and been using

Please have a look at the pictures in post 29
Even when following DJI's instructions to the letter, the lower blades have to be deflected slightly to fit underneath the other pair

 

[TruGreen]

Please have a look at the pictures in post 29
Even when following DJI's instructions to the letter, the lower blades have to be deflected slightly to fit underneath the other pair

i saw the pics. im telling you my drone new from box was not like that. my blades both sides top and bottom when folded are parallel with the body and not pointing upwards like the images posted

 

[LotusFan]

i saw the pics. im telling you my drone new from box was not like that. my blades both sides top and bottom when folded are parallel with the body and not pointing upwards like the images posted

I don't get that, the rear motors are canted outwards slightly when the arms are folded - unless they've subtly modified the arms, this is why the motor speed error is almost always on the rear and on the side that folds underneath the other

 

[Zbip57]

My blades don't push down. They simply cross cross.

My props folded together easily as well, and I never gave it a thought. It didn't matter if I slid them together right over left, or left over right. They meshed together easily. My Mini was always carefully stored in its Fly More case since I bought it in December 2019.

However, on my very first flight after upgrading to the latest firmware (v01.00.0500) that came out in April 2020, I received the Motor Speed Error warning message, telling me to replace the propeller blades on the left-rear motor. There was nothing visibly wrong with any of the prop blades. No knicks, scratches, cracks or anything that I could see. But I had spare prop blades, so I replaced them as instructed.

The difference was only evident when comparing the new blades to the old when mounted on the MIni. I wish I had taken a photo before replacing the left-rear blades, but this is what it looked like comparing the original right-rear versus brand new left-rear blades.

Note how the new left-rear blades are standing straight and high, whereas the old right-rear blades touch the body of the Mini. That's even before wedging the right-rear blades under the left-rear for "proper" storage in the Fly More case.

If your blades slide easily together, they're almost certainly already bent.



The problem is that the motors are mounted at angle. The rear motors are tilted approx 5° outboard, whereas the front motors are tilted rearward.



Have a close look at yours. The outward tilt of the rear motors is quite evident.



With new prop blades installed on BOTH rear motors, you can see how high the tips of the blades are. The blades cross. They don't slide easily under the opposite side unless the tips are bent down.



Forcing the blade tips down on the rear motors to fit under the opposite side bends the blades and twists them.



It's not an issue on the front motors because those motors are not tilted to the side.



The front blades therefor mesh together easily without bending when positioned laterally across the body.