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The problem with the propellers
1709 22 2022-2-19
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djiuser_nO2RdSW5BSUg
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I would like to point out a certain danger that occurs when starting engines, especially at low temperatures, when the plastic of the propellers becomes brittle. Rapid engine take-off combined with propeller inertia may result in later failure in flight.
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2022-2-19
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Sean-bumble-bee
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Good catch.
How many blades are damaged? If only 1 it may be a fluke, or could the damage have another source? Have you checked the hub of the other blade to see if there is a protrusion that could be responsible?
When starting the Motors in the cold you could position the blades so that the trailing edge of one blade is against the hub of the other blade, that would probably lessen the 'smack' on motor start.
2022-2-19
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djiuser_nO2RdSW5BSUg
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This is the third one that I am replacing with new ones. There is no rule, this applies to all engines. Now, I am starting to straighten the propellers before takeoff the drone. Before, I had heard the click of a propeller hitting the attachment point.
2022-2-19
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DAFlys
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Always straighten the props before take off.
2022-2-20
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No Original Thought
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DAFlys Posted at 2-20 01:20
Always straighten the props before take off.

I think I even read that in the manual somewhere...
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DAFlys
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No Original Thought Posted at 2-20 01:35
I think I even read that in the manual somewhere...

Someone made a slow mo that showed the stress difference and it was quite remarkable the extra wobble the closed props caused.
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No Original Thought
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DAFlys Posted at 2-20 01:38
Someone made a slow mo that showed the stress difference and it was quite remarkable the extra wobble the closed props caused.

I'm going to add it to my checklist.
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DAFlys
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No Original Thought Posted at 2-20 01:42
I'm going to add it to my checklist.

That's a good idea N.O.T.
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Sean-bumble-bee
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If "straighten" means put them in the flying positions, then the Minis are something of an oddity and straightening will not work.

Mini propellor blades are so free to rotate about their pivots that when the motor is started I would bet that the blades are 'left behind' and end up in the position shown in these photos, once there the blades will start to move with the motor but in getting "there" they will hit the the shoulder of their partner blade with a smack each time. As proof take note of the position the blades end up in each and every time the motors stop, (the motors are actively braked) it is the reverse of the photos, i.e the leading edge of each blade is against the shoulder of its partner.


If you wish to reduce the chances of this chipping happening then I think the blades should be positioned AS SHOWN in the photos PRIOR TO motor start. That would mean that as soon as the motors start to turn so do the blades and thus the trailing edge of a blade does not smack into the shoulder of its partner.

The 'stiff' pivots of other Mavics are stiff enough to hold the individual blades in the postion they are set to, look at the position the blades end up in when their motors are stopped, more or less the normal flying position.
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JJB*
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Sean-bumble-bee Posted at 2-20 03:09
If "straighten" means put them in the flying positions, then the Minis are something of an oddity and straightening will not work.

Mini propellor blades are so free to rotate about their pivots that when the motor is started I would bet that the blades are 'left behind' and end up in the position shown in these photos, once there the blades will start to move with the motor but in getting "there" they will hit the the shoulder of their partner blade with a smack each time. As proof take note of the position the blades end up in each and every time the motors stop, (the motors are actively braked) it is the reverse of the photos, i.e the leading edge of each blade is against the shoulder of its partner.

Just had a check on my 8 blades, not a sign of any damage or dents or anything...
This after many many flights, in cold tempersature as well.

Would love to see a slow-slow-motion of how the blades moves at starting the motors.

cheers
JJB
2022-2-20
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Sean-bumble-bee
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JJB* Posted at 2-20 03:18
Just had a check on my 8 blades, not a sign of any damage or dents or anything...
This after many many flights, in cold tempersature as well.

What position do your Mavic Mini blades end up in when the motors are stopped? The opposite of the photos in the opening post? They do with all my minis, every time.
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Sean-bumble-bee
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JJB* Posted at 2-20 03:18
Would love to see a slow-slow-motion of how the blades moves at starting the motors.

I just shot one, 120 fps, the blades were set with their leading edges against the shoulder of their partner, the motors started via a CSC. Before it started proper the motor focused on twitched in reverse (counter clockwise) 1? pole then stopped. This threw the blades out to near enough straight. When the motor then started (clockwise), the blades, orientation wise, stayed more or less where they were in space whilst the shoulder of the other blade came round to 'whack' into the trailing edge. Being honest you could probably do with a faster frame rate.
Start of the twitch to the first whack is 34 frames inclusive.
I am not set up to post video sorry.

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No Original Thought
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Sean-bumble-bee Posted at 2-20 03:09
If "straighten" means put them in the flying positions, then the Minis are something of an oddity and straightening will not work.

Mini propellor blades are so free to rotate about their pivots that when the motor is started I would bet that the blades are 'left behind' and end up in the position shown in these photos, once there the blades will start to move with the motor but in getting "there" they will hit the the shoulder of their partner blade with a smack each time. As proof take note of the position the blades end up in each and every time the motors stop, (the motors are actively braked) it is the reverse of the photos, i.e the leading edge of each blade is against the shoulder of its partner.

I did wonder about exactly that - what the best startup position would actually be.

Thinking about the props not picking up speed quick enough due to their inertia, I wondered if putting them in the 'hit' position to start with might help then it would be a static force rather than a moving force, but that twitch would put paid to that idea.

I'm guessing, then, there's probably not much we can do to prevent it...

Would still be interested in seeing a slo-mo video of the props at startup, though.

My other halfs phone does great super-slo-mo but it's really hard to time it!
2022-2-20
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Sean-bumble-bee
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Yep the twitch was a surprise/disappointment, I might try another motor or drone but not tonight. I used a hand held M2P as a camera and switched the bottom light on. The light might pulse at 60Hz, alternate frames were light and dark. Two tiny bits of rubber (elastic bands) or soft silicon glued to the blade hubs perhaps?
2022-2-20
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JJB*
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Hi,






Action2 cam in 8x slow motion, in post 5x slower....


Cheers
JJB




2022-2-21
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Dale 68
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Interesting. no damage on mine yet
2022-2-21
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Montfrooij
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No Original Thought Posted at 2-20 01:35
I think I even read that in the manual somewhere...

There are video's showing the difference (they were shared on this forum long time ago).
2022-2-21
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Montfrooij
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Dale 68 Posted at 2-21 01:39
Interesting. no damage on mine yet

I think mine are good too (but will check before the next flight)
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Sean-bumble-bee
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Interesting, that looks as if any twitching depends on the position of the motor's rotor.
2022-2-21
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smbishop
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JJB* Posted at 2-21 01:27
Hi,

https://vimeo.com/679927021

Thank you for sharing the videos!
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JJB*
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smbishop Posted at 2-21 08:25
Thank you for sharing the videos!

thanks, its my pleasure   and fun to test the action2 cam
2022-2-21
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blue_canyon21
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I've had the same propellers on mine for 203 flights and they show no signs of damage like above. I've flown in temperatures ranging from -10C to around 42C (28F to ~108F) and in both light rain and snow. I've even flown with them in wind so bad the drone didn't make it home.
2022-2-21
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blue_canyon21
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I remember seeing either on here or the Mini 2 subreddit a guy that 3d printed a set of brackets(?) that would hold the propellers straight during flight. Maybe something like that would help you out. If I find it, I'll post a link here.
2022-2-21
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