Mavic Mini random noise in flight - Props?

[Johnnydxxx]

I noticed lately some worrying clicking sound coming From my Mavic Mini while in descent or hovering. It's not a constant sound but a sudden whack as if the props had hit something even though in clear air. The 1st time it happended I immediately landed to inspect the Mini and couldn't see any damage to props or drone. I put it down to the Mini props hitting a Bee or large insect.

Since then it's happended again on a few occasions and on close inspection I found a very small nick at the very end of one of the props. Strange because this Mini has never landed on anything other than a pad and there are absolutely no impact marks on the drone body or arms where the prop could have come into contact with. So I have another theory? The propellers on the same arm have almost 'folded' it flight and one has 'kicked' the other. After all is's only centrifugal force that keeps them fully extended. The 2nd part of my theory comes from my experience flying a Hubsan drone that didn't have stabalised gimbal. The Hubsan along with my paragliding experience made me very aware of prop-wash and wind turbulance and what it can do to an aircraft. With the Hubsan if you descended straight down in calm conditions the drone would wobble and shake due to descending through it's own down-wash and the footage would be useless. However, if you left the wake turbulance behind by coming in at a glide angle the drone was stable and so was the footage. So if you are in a hover or descending the downwash mixed with a gusty wind could 'stall or accelerate' one of the Mini props causing it to lag and be kicked by it's partner on the same arm. It's not something that coud happen with the Hubsan's non folding props. I see there's a couple of older posts regarding Mavic Mini random 'clicking' in flight where changing props didn't solve it, but my theory has not been put forward before. What do you think?

As a side note regarding props if you've ever seen a slow mo of a Mini Starting up with props not fully extended you will always tease out your props to be sitting fully extended before start up as I do now. (providing it's not windy enough for it to blow them around 1st

 

[old man mavic]

@Johnnydxxx this is a phenomenon that has been present since the first release of the original MM
and it has been attributed to various reasons since then ,a big issue with the first incarnation of the MM was to do with the actual storage bag that came with the fly-more package
its design meant that when the drone was in the case it could apply pressure to the props folded under the drone and cause them to loose some of the aerofoil shape ,this would lead to a loss of lift and motor overload warnings during flight especially in fairly windy conditions
and it also caused the props to make contact with the body of the craft if it was windy
when this happened to me ,i started to investigate why and i found that the front arms were very flexible compared to the rear ones
i felt that this could be a contributing factor to the prop strike issue ,so using an old credit card i made some pieces that i stuck to the rear of the arms
this made the front arms as stiff as the rear ones ,and for me totally stopped the prop strike problem from happening
i left the soft foam insert in the arms and carefully stuck the shaped pieces of card to the rear edge of the front arms ,which basically turned them into a box girder section
i have hundreds of flights with my MM since then with out any problems,a few people started printing inserts for the front arms to replace the foam, the whole process adds a miniscule amount of weight and does not take the drone over the 250g limit
i do not claim to be the inventor of this fix ,but all i do know is it works,to eliminate the props being distorted in the case i purchased a hard case to carry the drone and also the DJI cover that goes over the props and clips on the drone and the hard case also eliminates the need to keep removing the control sticks per the original case

 

[Deleted member 103366]

I think the theory of the props swing on their pivots enough to collide with one another is highly unlikely. If I understand your suggestion correctly that would require one blade to be stuck and the other to swing through almost 180deg about its pivot, what could cause that?

Sudden accelerations of the motor may indeed cause a blade to swing about its pivot but the swing would happen to both blades and the movements would, I suspect, be limited except during motor start and stop.

Just look at and think about the position of the blade when you stop the motors, with mine they are always thrown forwards with respect to (wrt) their normal direction of movement/rotation and the shoulder of the leading edge of one blade is against the hub of the other.
I.e. the motors hubs are braked, either by their inherent magnetism or by actively applied energisation of the motor poles, either way they slow more rapidly than the blades and the blades therefore move forward wrt their pivots.

Aside from that would not your theory would have the leading edge of one blade hitting the trailing edge of the other, of so are not the trailing edges weaker than the leading edges?
The damage to your blade seems to be to the leading edge.

 

[Johnnydxxx]

Aside from that would not your theory would have the leading edge of one blade hitting the trailing edge of the other, of so are not the trailing edges weaker than the leading edges?
The damage to your blade seems to be to the leading edge.

@PhiliusFoggg That's interesting but Im sticking to my theory at moment. 2nd photo shows a position props could be in with abrasion where silver paint rubbed off on lower prop caused by underside of other prop. A leading edge wouldn't hit a trailing edge as the prop is tilted. Both leading edges are higher so lower trailing edge on one would drag over leading edge of other. Bottom prop had a tiny sliver of plastic missing. Heat friction on one shaft making it stick or lag momentarily?

 

[Deleted member 103366]

Ahhh well good luck then.
Just as matter of interest are there any scuff marks or paint transfers on the underside of the relevant blade.
Friction and heat in the pivot, I think unlikely, I would be surprised if the props move about enough to generate any heat from friction. Besides which the props of all my minis are remarkable frictionless on their pivots, to the extent that the move under their own weight when the drone is tilted. I'd be more inclined to check for loose screws.

 

[Johnnydxxx]

Ahhh well good luck then.
Just as matter of interest are there any scuff marks or paint transfers on the underside of the relevant blade.
Friction and heat in the pivot, I think unlikely, I would be surprised if the props move about enough to generate any heat from friction. Besides which the props of all my minis are remarkable frictionless on their pivots, to the extent that the move under their own weight when the drone is tilted.

You're right there would be no friction or heat build up as the props are not rotating on their screw shafts. Anyone ever thougt about lubricating them? Have some prop shaft lubicant from Hubsan days

 

[Johnnydxxx]

@Johnnydxxx this is a phenomenon that has been present since the first release of the original MM
and it has been attributed to various reasons since then ,a big issue with the first incarnation of the MM was to do with the actual storage bag that came with the fly-more package
its design meant that when the drone was in the case it could apply pressure to the props folded under the drone and cause them to loose some of the aerofoil shape ,this would lead to a loss of lift and motor overload warnings during flight especially in fairly windy conditions
and it also caused the props to make contact with the body of the craft if it was windy
when this happened to me ,i started to investigate why and i found that the front arms were very flexible compared to the rear ones
i felt that this could be a contributing factor to the prop strike issue ,so using an old credit card i made some pieces that i stuck to the rear of the arms
this made the front arms as stiff as the rear ones ,and for me totally stopped the prop strike problem from happening
i left the soft foam insert in the arms and carefully stuck the shaped pieces of card to the rear edge of the front arms ,which basically turned them into a box girder section
i have hundreds of flights with my MM since then with out any problems,a few people started printing inserts for the front arms to replace the foam, the whole process adds a miniscule amount of weight and does not take the drone over the 250g limit
i do not claim to be the inventor of this fix ,but all i do know is it works,to eliminate the props being distorted in the case i purchased a hard case to carry the drone and also the DJI cover that goes over the props and clips on the drone and the hard case also eliminates the need to keep removing the control sticks per the original case

Amazing will check out. I always install the lower props correctly in the DJI FLY combo case so they hang and notice the top props are under no pressure from top cover. I also find I can leave sticks on and strore a VIFLY strobe under battery pack and a landyard under controller in the Fly More Combo case. Happy days!

 

[old man mavic]

@Johnnydxxx ,yes it is possible to leave the sticks on in the original case ,but just remember that the case is then applying some pressure to the stick gimbals especially if you put something on top of the case
with regards to you question about lubricant best advise i can give you is dont
two things could happen it could affect the plastic the props are made of and if it gets in to the motors then it will a cause dust etc to stick to the inside of them
i have a bottle of special motor lube from back in the day when it was part of the maintenance routine to lube up the motor bearings in my early drones ,but i would never use it in any of my Mavics ,or indeed my new Hubsan Zino Mini SE

 

[Capt KO]

Agree with OMM that the props hit the body on the MM1 after storage in the case. Changing props stops the problem temporarily. I used plastic caps over the props in the case and stopped the problem. Stiffening the front arms was used by many also. Sold mine and upgraded to a used A2. It’s awesome but still miss that fun little bird.