Mavic Mini prop has unstable shape ?

[new2mavic]

OK, I am bored today so I did a small experiment on my Mini. I have noticed for some time that when hovering in a windless environment, the revolution speed of the motors at the back is significantly higher than those of the front motors. This is not good because it means the motors at the back will reach their speed limit sooner so the overall power of the craft is reduced.

I have been suspecting that the higher revolution speed is caused by the pitch of the props reduced for some reasons. To verify this I swapped the front props with those at the back and checked the motor speeds when hovering indoor.

Original prop installation :


Props swapped :



So what I have suspected turns out to be true ! The props at the back have lower pitch and after they are installed on the front motors, the revolution speed of the front motors becomes higher !

My Mini is very new, less than 10 flights. No crash or hard landing.

This opens up further questions :

1) How is the pitch of the props at the back changed ? can it be due to the fact that they are being sit on by the craft when stored inside the case that came with the drone ?

2) Does this explain the numerous reported crash cases of Minis in which some motors have the power maxed out and the craft failed to tilt to the commanded angle before it fell out of the sky ?

3) How can the problem be solved ? Are there any better props out there ? Hope third-party prop makers are listening.

Any comments ?

 

[Tornestam]

Can you actually see any "damage and or distorsion" on the props? When I look very close I might see a slight little bend on one of the rear props. Or maybe not... I mean it is that small and they should have some tolerance you think since it is resting on them in the flight case.

 

[new2mavic]

Can you actually see any "damage and or distorsion" on the props?

Absolutely none

 

[Meta4]

I have been suspecting that the higher revolution speed is caused by the pitch of the props reduced for some reasons.

So what I have suspected turns out to be true ! The props at the back have lower pitch and after they are installed on the front motors, the revolution speed of the front motors becomes higher !

Have you measured the props or are you making assumptions?
It's quite normal for the motors to have different speeds and the flight controller will adjust all 4 motor's speeds as appropriate.
The flight controller probably could also deal with minor prop differences.

1) How is the pitch of the props at the back changed ? can it be due to the fact that they are being sit on by the craft when stored inside the case that came with the drone ?

That's unlikely.
Lots of others would be complaining if it was.

2) Does this explain the numerous reported crash cases of Minis in which some motors have the power maxed out and the craft failed to tilt to the commanded angle before it fell out of the sky ?

All the sinking Mini data I've seen has a Mini flying quite normally for some time before it just gives up tilting properly.
If it was due to a problem with props, they wouldn't fly properly at all.

3) How can the problem be solved ? Are there any better props out there ? Hope third-party prop makers are listening.

I've not heard of any problem with DJI props previously.
Make certain there is a problem with the props before trying to "solve"it.

 

[old man mavic]

when you did your test were you indoors hovering
if there was absolutely no external wind force on the drone, which includes propwash from the walls or object close to the drone
then swapping the props front to rear would make no difference at all, in still air theoretically all the props should be spinning at the same speed to keep the drone in one spot

 

[Tornestam]

I took the back props and compared with a magnifier glass and I could not see any difference at all. Tried to fly it a couple of more times today, better light and less wind inside my inner yard. It could not take off with auto-app nor the manual forced (left up) that worked yesterday. I tried forced up AND forward. got it to lift but it hovered badly like a lost chicken and I did not get it into stable flight and land properly. I lowered with the manual sticks until it reach the ground and flipped backwards. I am taking it back to the store.
Thank you all for engaging and giving tips. Also translating the data to graphs. Thank you!

 

[sar104]

OK, I am bored today so I did a small experiment on my Mini. I have noticed for some time that when hovering in a windless environment, the revolution speed of the motors at the back is significantly higher than those of the front motors. This is not good because it means the motors at the back will reach their speed limit sooner so the overall power of the craft is reduced.

I have been suspecting that the higher revolution speed is caused by the pitch of the props reduced for some reasons. To verify this I swapped the front props with those at the back and checked the motor speeds when hovering indoor.

Original prop installation :
View attachment 93302

Props swapped :

View attachment 93303

So what I have suspected turns out to be true ! The props at the back have lower pitch and after they are installed on the front motors, the revolution speed of the front motors becomes higher !

My Mini is very new, less than 10 flights. No crash or hard landing.

This opens up further questions :

1) How is the pitch of the props at the back changed ? can it be due to the fact that they are being sit on by the craft when stored inside the case that came with the drone ?

2) Does this explain the numerous reported crash cases of Minis in which some motors have the power maxed out and the craft failed to tilt to the commanded angle before it fell out of the sky ?

3) How can the problem be solved ? Are there any better props out there ? Hope third-party prop makers are listening.

Any comments ?

Just to clarify - are the four props nominally identical - i.e. not identified as front and rear?

 

[new2mavic]

when you did your test were you indoors hovering
if there was absolutely no external wind force on the drone, which includes propwash from the walls or object close to the drone
then swapping the props front to rear would make no difference at all, in still air theoretically all the props should be spinning at the same speed to keep the drone in one spot

Yes, it's indoor and windless.

"....theoretically all the props should be spinning at the same speed to keep the drone in one spot...." is true only if all the props are identical. The experiments proves that they are not and the difference is not insignificant at least for my Mini.

 

[new2mavic]

Just to clarify - are the four props nominally identical - i.e. not identified as front and rear?

Yes, there is no difference between front and rear props.

 

[sar104]

Yes, it's indoor and windless.

"....theoretically all the props should be spinning at the same speed to keep the drone in one spot...." is true only if all the props are identical. The experiments proves that they are not and the difference is not insignificant at least for my Mini.

Actually you wouldn't expect all the props to be spinning at the same rate unless (1) they are all equally spaced around the center of mass and (2) the aircraft is completely symmetric so that the airflow from each prop is the same.

 

[sar104]

Yes, there is no difference between front and rear props.

So the hypothesis is that the rear ones are becoming deformed when the aircraft is folded and stored? If so then it would be nice to see the results of that experiment with all new props.

 

[Mavic_Mini_Pilot]

I took the back props and compared with a magnifier glass and I could not see any difference at all. Tried to fly it a couple of more times today, better light and less wind inside my inner yard. It could not take off with auto-app nor the manual forced (left up) that worked yesterday. I tried forced up AND forward. got it to lift but it hovered badly like a lost chicken and I did not get it into stable flight and land properly. I lowered with the manual sticks until it reach the ground and flipped backwards. I am taking it back to the store.
Thank you all for engaging and giving tips. Also translating the data to graphs. Thank you!

That is very strange hey! I've never had even one problem with my Mavic Mini! I really do like this drone lots and lots! About the propellers being/having an unstable shape, that is likely not true. I spoke with DJI Support about the material of the props and if it matters that the drone rests on the props sometimes and also I specifically asked about my Propeller Holder! See my Propeller holder, the exact same one that is in my profile pic, the one the drone rests in - has a leather strap on the top which straps the front(folded-in) legs propellers. So basically this Strap is a bit tight, as it should be! I was worried that its so tight that the way its pressing down on the front props, pressing them against the top body shell, would change their shape permanently as the drone stays all the time in its lil holder with the strap. actually it has that 100% of the time its not flying! So I could see and feel, by moving the blades a bit while strapped-in, that the props have some pressure excreted on them by the actual strap itself! The way the blades stack one on top of the other, in order, just below the strap holding them have some pressure constantly excreted on them.

DJI Support (and I spoke to 2 different support agents & both said the same thing), told me that the propellers are made out of a new composite extremely flexible material which cannot easily take another shape to keep! They are made very thin, with a very flexible overall structure! I was assured that no matter how I strap my blades, as long as I use the Propeller Strap correctly(as intended) that the props will take the required shape when I unstrap them out of the holder!

You know it does make sense that your findings have something to do with the Minis losing altitude without being commanded to! If what you are saying is true and some props (back ones) have to spin faster than others (front ones) - then that means that there may come a point in time during the flight where the drone has to fight normal, natural winds! These winds may be very strong and the Mini may be able to fight them and fly through them say in Sports mode - BUT, but, but - the drone may reach a point in time during this wind fighting where it needs to pitch forward but cannot because of not enough pitch or RPM on the back motors, I think this is when the Not Enough Force/ ESC Error comes up - or similar situations!

So all-in-all the props are extremely flexible, and we should not worry about the drone resting on them, or propeller straps pressing them down hard, propeller tips one against the other, all 4 stacked over one point where their folded tips meet under the actual strap! DJI assured me not to worry, and so I will listen to them and just be cool. Although if I could somehow get other propellers to try, ones with more pitch, so that the Mini can save up on RPM and use them if needed.

cool cool

 

[Mavic_Mini_Pilot]

So the hypothesis is that the rear ones are becoming deformed when the aircraft is folded and stored? If so then it would be nice to see the results of that experiment with all new props.

I really don't believe this hey, like I said in my previous post, I have asked DJI Support twice about this. I noticed when using the Drone Holder - same color as the drone itself, which has a leather strap for the 2 front folded-in arm's 4 propellers - that this leather strap was actually pressing down so hard on the stacked props' tips that it could actually deform them propellers!

I asked DJI Support for help on this and as you've read in my previous post, they say that the propellers are made of some extremely flexible, composite material, which has the ability to change its shape as it is very flexible, but in the end (when you take off the strap) when no pressure is excreted on the blades - they should take their normal, usual form again very quickly! In fact DJI Support told me to look for chips and dents on the props as unbalanced propellers will cause Flight Stability issues and make it difficult for the FC to work!

So I'm like super scared and afraid that I might have bent them, deformed them - but apparently not!

cool cool

 

[Saigondroner]

OK, I am bored today so I did a small experiment on my Mini. I have noticed for some time that when hovering in a windless environment, the revolution speed of the motors at the back is significantly higher than those of the front motors. This is not good because it means the motors at the back will reach their speed limit sooner so the overall power of the craft is reduced.

I have been suspecting that the higher revolution speed is caused by the pitch of the props reduced for some reasons. To verify this I swapped the front props with those at the back and checked the motor speeds when hovering indoor.

Original prop installation :
View attachment 93302

Props swapped :

View attachment 93303

So what I have suspected turns out to be true ! The props at the back have lower pitch and after they are installed on the front motors, the revolution speed of the front motors becomes higher !

My Mini is very new, less than 10 flights. No crash or hard landing.

This opens up further questions :

1) How is the pitch of the props at the back changed ? can it be due to the fact that they are being sit on by the craft when stored inside the case that came with the drone ?

2) Does this explain the numerous reported crash cases of Minis in which some motors have the power maxed out and the craft failed to tilt to the commanded angle before it fell out of the sky ?

3) How can the problem be solved ? Are there any better props out there ? Hope third-party prop makers are listening.

Any comments ?

The props seem to be made of jelly. And the front arms are very flimsy, compared to the back. I have ordered some carbon fiber props, that will be stiff as a board. My guess is they will affect the MM's airframe.

I may try DJI props in front, CF's in the back, 10m max. I'm bored as well.

 

[sar104]

I really don't believe this hey, like I said in my previous post, I have asked DJI Support twice about this. I noticed when using the Drone Holder - same color as the drone itself, which has a leather strap for the 2 front folded-in arm's 4 propellers - that this leather strap was actually pressing down so hard on the stacked props' tips that it could actually deform them propellers!

I asked DJI Support for help on this and as you've read in my previous post, they say that the propellers are made of some extremely flexible, composite material, which has the ability to change its shape as it is very flexible, but in the end (when you take off the strap) when no pressure is excreted on the blades - they should take their normal, usual form again very quickly! In fact DJI Support told me to look for chips and dents on the props as unbalanced propellers will cause Flight Stability issues and make it difficult for the FC to work!

So I'm like super scared and afraid that I might have bent them, deformed them - but apparently not!

cool cool

If your belief is based purely on DJI's assurance to you that it won't happen, then that is completely outweighed by the data presented above which conclusively showed that the props are now different. Either they were made that way, and for some reason always end up on the rear motors, or they are deformed in use/storage.

 

[Mavic_Mini_Pilot]

If your belief is based purely on DJI's assurance to you that it won't happen, then that is completely outweighed by the data presented above which conclusively showed that the props are now different. Either they were made that way, and for some reason always end up on the rear motors, or they are deformed in use/storage.

I honestly think that it just the props on one guy's drone, which other guy or drone is complaining of this same effect here? Even if there are 2 or 3 people complaining of this same issue I'm more likely to believe that its just a coincidence that the back ones are lessening their pitch as a result of storing the drone on its own weight on the back props. When I strap my Mini in its lil holder the drone still lays/rests on its folded-in rear arm's propellers (just like if I didn't have the Holder) and the front propellers get strapped down very securely via the leather strap - so there is pressure on the bottom propellers and the top ones - and I've never had any problems with my Mini..... .....yet!



A good way to check if what you think is true, that the propellers are getting deformed or something, is to just swap them around. Put the front ones at the back and the back ones in the front. Keep it this way for as long as you need to prove to yourself that this does indeed happen(weeks probably). Then do the measures again of the hovering RPM & make a conclusion.

But you area very smart man, so you're probably correct about all this - if it is true then maybe we can carefully give some of that missing pitch back by just modifying the props by hand and gently giving them some more pitch. Not sure, but I'd really like to find out the truth about this.

cool cool

 

[sar104]

I honestly think that it just the props on one guy's drone, which other guy or drone is complaining of this same effect here? Even if there are 2 or 3 people complaining of this same issue I'm more likely to believe that its just a coincidence that the back ones are lessening their pitch as a result of storing the drone on its own weight on the back props. When I strap my Mini in its lil holder the drone still lays/rests on its folded-in rear arm's propellers (just like if I didn't have the Holder) and the front propellers get strapped down very securely via the leather strap - so there is pressure on the bottom propellers and the top ones - and I've never had any problems with my Mini..... .....yet!



A good way to check if what you think is true, that the propellers are getting deformed or something, is to just swap them around. Put the front ones at the back and the back ones in the front. Keep it this way for as long as you need to prove to yourself that this does indeed happen(weeks probably). Then do the measures again of the hovering RPM & make a conclusion.

But you area very smart man, so you're probably correct about all this - if it is true then maybe we can carefully give some of that missing pitch back by just modifying the props by hand and gently giving them some more pitch. Not sure, but I'd really like to find out the truth about this.

cool cool

There have been multiple documented reports of overspeed and lack of lift from MM rear props. I'm currently compiling those data to post a summary. And swapping them around is exactly what @new2mavic did and reported on in post #1 in this thread.

 

[Mavic_Mini_Pilot]

There have been multiple documented reports of overspeed and lack of lift from MM rear props. I'm currently compiling those data to post a summary. And swapping them around is exactly what @new2mavic did and reported on in post #1 in this thread.

Yes but he just swapped them around, he put the back in front and vice versa! I mean that he should keep them swapped like this for long and rest his drone like this all swapped, and measure after a long time of resting on the new back props. You can't just swap them, that doesn't prove that the back ones get deformed over time.

cool cool

 

[sar104]

Yes but he just swapped them around, he put the back in front and vice versa! I mean that he should keep them swapped like this for long and rest his drone like this all swapped, and measure after a long time of resting on the new back props. You can't just swap them, that doesn't prove that the back ones get deformed over time.

cool cool

Well the alternative is that they were deformed originally, which goes back to the observation that it would be rather surprising if the deformed props always end up on the rear motors.

 

[Mavic_Mini_Pilot]

Someone who has scuffed-up or damaged props should try to bend them by hand and see where the threshold is more or less and this way we can try to form a bit of extra pitch where needed and adjust accordingly. I'm just still super happy with my unit and don't wanna mess around with it at all.

The most I've done is just the FCC Hack to my CE version, as I fly in Sofia City and its extremely clustered with Wi-Fi. The FCC Hack on CE models does indeed extend the range of the CE version to about 1.3 km which is amazing and what I want in my city.

cool cool