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What happens if a motor is blocked mid air?
837 29 8-21 01:32
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fgange57
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For some days ago my Mini 4 pro was attacked three consecutive time by a bird of prey. Each of the time at least one of the motors stopped, but for some reason, each time when the bird let go, the motors luckily started up again and the drone levelled up, and I finally got it back (without any visible damages - perhaps apart from emotional ones :-)). Looking at the footage on how the drone was manhandled, I was surprized that the engine restarted.

Can this be expected or was I only lucky this time?

I have created a video where I have included the flight recorder from a screen recording on the RC 2. You can really see the drone moving in a strange way.  I also picked pictures out of some of the frames showing the bird that attacked the drone.




8-21 01:32
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DowntownRDB
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Fortunately, the motors restarted.  If one fails it will no longer be controllable and the drone will undoubtedly crash.  

If you see birds approaching your drone the fastest way to avoid them is to ascend rapidly.  Birds can descend fast but not ascend as fast.  If you have time switch into sport's mode to give you more speed in the ascent.  

I do my best to avoid areas where birds are prevalent on a daily basis.
8-21 14:02
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Labroides
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I was surprized that the engine restarted.
It just detected resistance but your motors never stopped.
8-21 14:28
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Burt37
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It has nothing to do with luck..

As the motors are in the open and encapsulate in aluminium, it will take some severe heat before they could fail... Depending on the temperature of the day, it would take several minutes for a motor to burn one of its filament...

But that should not really happen on a DJI drone as they have a built in protection mode for the rotors and the ESC...

When one of the motor is stuck, the ESC will reduce the voltage to a minimum level to prevent overheating. If the motor does not freely moves under the reduce voltage, after a specific amount of time (in seconds), the voltage is cut off completely, as the motor has now become a huge resistor and it could easily burn the ESC...

You can test this by hovering the drone in very tall grass. The radio will also give you a visual warning or the motors not being able to rotate freely...

Back in the old days, it was a lot easier to fry the ESC than the actual motor...  With DJI choosing the correct combo of ESC, motor size and blades, this should be a non issue on their drones...

8-21 14:36
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Sean-bumble-bee
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Burt37 Posted at 8-21 14:36
It has nothing to do with luck..

As the motors are in the open and encapsulate in aluminium, it will take some severe heat before they could fail... Depending on the temperature of the day, it would take several minutes for a motor to burn one of its filament...

All probably correct except for
" now become a huge resistor..",
a stopped motor is a short circuit, near zero resistance, meaning huge currents would flow through it, it is probably these currents that can cook an ESC.
This is why big motors sometimes have/had special starting ciruits..
8-21 16:33
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Burt37
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Sean-bumble-bee Posted at 8-21 16:33
All probably correct except for
" now become a huge resistor..",
a stopped motor is a short circuit, near zero resistance, meaning huge currents would flow through it, it is probably these currents that can cook an ESC.

I really don't see the word stopped anywhere in my post...

If the motor had stopped the drone would have crashed. Even Labrodies mentioned that...

Perhaps the word stuck, got you to think that I meant stopped,but no... I meant when the bird was preventing the motor from spinning freely, in relation to the OP...

While the rotor is preventing from spinning freely, being a brushless motor, it does act as a huge resistor (overloaded) until it completely stop at which point the ESC removes the power to prevent the filaments from burning, melting and creating a short...

With most new Drones, when the motor has stopped either by command or by accident there is no short circuit possible, as there is no voltage coming out of the ESC...

8-21 19:55
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Sean-bumble-bee
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Maybe it is American vs British but to me a "resistor", large or small, is part of an electrical circuit that opposes the passage of an electrical current via "resistance", measured in Ohms. Motor windings, by design, have very little resistance, small fractions of an Ohm.
Most of a running motor's opposition to the passage of current through its windings comes from a "back emf" induced in the windings by the rotating magnetic field that surrounds those windings.
When the motor is running well below its desgined speed, which includes stalled/stopped, the back emf is greatly reduced and the current 'soars'.

With regards the action of a bird on a motor, unless the bird is actually grasping the motor's rotor or is pressing down on the propeller blades etc. then it opposes the rotation of the motor by blocking the rotation of its prop.
Try this with a not powered on drone, put your finger inside the area swept by the prop blades and then turn the motor by hand. I bet you find that your finger at some point stops the rotation of one blade by blocking the rotation of it and that blade will come up against a stop of some sort,  with my mini 1 & 2 the impeded blade comes up against the hub of the other blade, At that point the motor can no longer turn.
Something similar happens with mavic 2 style props. In fact with an in flight Mavic 2 the stopping of the motor causes the not blocked blade to whip around and smack into the trailing edge of the blocked blade and the not blocked blade takes a chunk out of the trailing edge if the blocked blade.

Unfortunately we probably can not check the motor rpms of a Mini 4 pro as their DATs are, from memory, encrypted but I am reasonably confident that the bird would have stopped the 'offending' motor rather  than significantly slowed it but left it turning at avery much reduced rate.


8-21 22:38
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fgange57
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DowntownRDB Posted at 8-21 14:02
Fortunately, the motors restarted.  If one fails it will no longer be controllable and the drone will undoubtedly crash.  

If you see birds approaching your drone the fastest way to avoid them is to ascend rapidly.  Birds can descend fast but not ascend as fast.  If you have time switch into sport's mode to give you more speed in the ascent.  

Thank you for your input, I have seen this comment of others having been attacked by birds and also done this successfully recently. With this bird, that can have a speed more that 300kmh, I never had a chance to see it. The drone suddenly wasn't there any more and the camera was all over. :-)
I also was unaware of birds in the area, and actually when I reported what I had seen, the responsible for the nature reserve were happy, because he did not know that these kind of birds were there.
8-22 00:09
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fgange57
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Labroides Posted at 8-21 14:28
I was surprized that the engine restarted.
It just detected resistance but your motors never stopped.

I have had the same message when hitting grass when landing, and then the propeller on that side definitely stopped, but if I understand you correctly, it is really just saying that the motors never stops, but will keep rotating when the resistance has gone?
8-22 00:14
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DJI Diana
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Hi there,
thank you for sharing this footage with us.

We're glad that nothing happened on your unit and that you manage to land the drone safely. Should you have any inquiries, please don't hesitate to reach us and we are more than happy to help. Happy flying always!
8-22 00:51
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Burt37
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Sean-bumble-bee Posted at 8-21 22:38
Maybe it is American vs British but to me a "resistor", large or small, is part of an electrical circuit that opposes the passage of an electrical current via "resistance", measured in Ohms. Motor windings, by design, have very little resistance, small fractions of an Ohm.
Most of a running motor's opposition to the passage of current through its windings comes from a "back emf" induced in the windings by the rotating magnetic field that surrounds those windings.
When the motor is running well below its desgined speed, which includes stalled/stopped, the back emf is greatly reduced and the current 'soars'.

A resistor does not oppose the passage of current... That's a diode

A resistor is designed to achieve a series of other jobs..

Probably the best way is to think of a resistor as a funnel (going form large to small) or a bottleneck when pouring water out


Have a look on wiki for a better explanation...

https://en.wikipedia.org/wiki/Resistor

8-22 01:26
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harweyko
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had similar encounter few months ago with different bird species, in my case drone was attacked from the side, not from above, bird was bit slower so obstacle sensors were able to detect him and brake the drone a bit, so the impact was not so serious as the drone was not hit to the place the bird planned to attack. I have had red reflective sticker on top and sides of the drone as proposed by some pilots, but it did not scared the bird away..
8-22 02:17
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Burt37
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harweyko Posted at 8-22 02:17
had similar encounter few months ago with different bird species, in my case drone was attacked from the side, not from above, bird was bit slower so obstacle sensors were able to detect him and brake the drone a bit, so the impact was not so serious as the drone was not hit to the place the bird planned to attack. I have had red reflective sticker on top and sides of the drone as proposed by some pilots, but it did not scared the bird away..

I found myself using the red reflective sticker as well after reading someone post here, but in my case, so far it has worked once. The bird came very quickly and very close, but then turned away without attacking... It seems to work with some birds but not with others...

I have also landed by mistake near a couple of ducks, and to my surprise they just looked at the drone about half a metre away, but then did nothing. They didn't move an inch... So I started the motors again and took off...
8-22 02:45
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Serg SSA
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Very beautiful views! Fantastic!
I will repeat what has already been said here, because I have experience with bird attacks and accidents. The motors did not turn off, they were overloaded and can work for a short time with such an overload until they turn off. If the motors turn off, they will not start again, the drone will fall. I repeat, the motors continued to be under load, it was not critical for switching off.
8-22 02:49
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fgange57
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harweyko Posted at 8-22 02:17
had similar encounter few months ago with different bird species, in my case drone was attacked from the side, not from above, bird was bit slower so obstacle sensors were able to detect him and brake the drone a bit, so the impact was not so serious as the drone was not hit to the place the bird planned to attack. I have had red reflective sticker on top and sides of the drone as proposed by some pilots, but it did not scared the bird away..

I have both yellow and red propellers and bright yellow tape (now also red reflective tape), but at least big birds don't care, they will attack anyway :-).
8-22 02:59
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Serg SSA
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fgange57 Posted at 8-22 02:59
I have both yellow and red propellers and bright yellow tape (now also red reflective tape), but at least big birds don't care, they will attack anyway :-).

I also said this, no reflective stickers scare away birds. I put a special bright strobe light on the drone, but it was useless too.
8-22 03:06
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fgange57
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Serg SSA Posted at 8-22 02:49
Very beautiful views! Fantastic!
I will repeat what has already been said here, because I have experience with bird attacks and accidents. The motors did not turn off, they were overloaded and can work for a short time with such an overload until they turn off. If the motors turn off, they will not start again, the drone will fall. I repeat, the motors continued to be under load, it was not critical for switching off.

What i did hear (bot not see, because the drone were moved far away) is that the other propellers seem to be working at full speed to stabilise the drone (as it was turned all around and apparently trying to get correct baring. Perhaps that is what let the bird to loose it.
8-22 03:07
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fgange57
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Burt37 Posted at 8-22 02:45
I found myself using the red reflective sticker as well after reading someone post here, but in my case, so far it has worked once. The bird came very quickly and very close, but then turned away without attacking... It seems to work with some birds but not with others...

I have also landed by mistake near a couple of ducks, and to my surprise they just looked at the drone about half a metre away, but then did nothing. They didn't move an inch... So I started the motors again and took off...

Currently I have both yellow and red propellers (fram Master Airscrew), bright yellow tape and also red reflective tape.  For a couple of days ago, I had a lot of swallows flying around the drone (but not attacking), but I chose to ascend and then they lost interest.
8-22 03:10
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fgange57
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Serg SSA Posted at 8-22 03:06
I also said this, no reflective stickers scare away birds. I put a special bright strobe light on the drone, but it was useless too.

I guess the best way is to keep a close eye out for birds and do evasive manoeuvring :-)
8-22 03:13
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Serg SSA
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fgange57 Posted at 8-22 03:10
Currently I have both yellow and red propellers (fram Master Airscrew), bright yellow tape and also red reflective tape.  For a couple of days ago, I had a lot of swallows flying around the drone (but not attacking), but I chose to ascend and then they lost interest.

Swallows never attack the drone, they fly around but do not attack or collide, they are good FPV pilots)
8-22 04:04
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Serg SSA
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fgange57 Posted at 8-22 03:13
I guess the best way is to keep a close eye out for birds and do evasive manoeuvring :-)

Unless it's a flock of pigeons)
8-22 04:46
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Labroides
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fgange57 Posted at 8-22 00:14
I have had the same message when hitting grass when landing, and then the propeller on that side definitely stopped, but if I understand you correctly, it is really just saying that the motors never stops, but will keep rotating when the resistance has gone?

That's correct ... we're not talking about a petrol engine here.
8-22 05:13
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fgange57
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Serg SSA Posted at 8-22 04:46
Unless it's a flock of pigeons)
https://youtu.be/8JWv_YWKOrc?si=Oklzy-sOEkpexlLP

Did your drone survive?
8-22 05:40
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fgange57
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Serg SSA Posted at 8-22 04:04
Swallows never attack the drone, they fly around but do not attack or collide, they are good FPV pilots)

They were anyway frying around the drone as I was flying slowly forward, but let go as soon as I went up, but I agree, the swallows are excellent aviators.
8-22 05:52
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Serg SSA
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fgange57 Posted at 8-22 05:40
Did your drone survive?

It was my friend's drone, it was slightly damaged.
At this point my drone managed to land.
8-22 06:34
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Serg SSA Posted at 8-22 06:34
It was my friend's drone, it was slightly damaged.
At this point my drone managed to land.
https://youtu.be/XPJ2pGrVCBI?si=rttFT3V6eqXaOoR2

Hi there, we're sorry to hear about what happened however we're glad that there's no any damages to your drone. Also, we appreciate you for sharing your experience and the remarkable footage with our DJI Forum community. Your contribution is highly valued and appreciated.

Safe flight always!
8-23 00:12
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VictorS
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You were flying too close to the birds nest. Two things we must respect when flying a drone: privacy and nature
8-24 07:14
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VictorS
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Serg SSA Posted at 8-22 04:46
Unless it's a flock of pigeons)
https://youtu.be/8JWv_YWKOrc?si=Oklzy-sOEkpexlLP

Facing the birds the best tactic is to go up. Going up or staying above the bird shows superiority. Eagles fly hight !
8-24 07:19
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fgange57
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VictorS Posted at 8-24 07:14
You were flying too close to the birds nest. Two things we must respect when flying a drone: privacy and nature

You are right, but then you also have to know if there is a nest there (even the responsible for the nature reserve didn't know, and was happy I informed them).

I will of course not fly there again.
8-24 07:32
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fgange57
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VictorS Posted at 8-24 07:19
Facing the birds the best tactic is to go up. Going up or staying above the bird shows superiority. Eagles fly hight !

It is just one thing: You have to see the bird coming first (and be able to react fast enough).
8-24 07:33
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