1. is there a way to tell if propellers are damaged or unsafe?
2. anyone experienced a propeller blade breakdown in mid-flight?
3. anyone experienced a motor breakdown in mid-flight?
4. DJI: would the drone be able to detect a malfunction at one rotor (motor or propeller) and eventually shut it down (automatically)?
5. would the drone be able to land on three propellers?
6. would she be able to RTH?
7. would the pilot be able to retain minimal control, as in avoiding water splash or landing over people?
I appreciate your answers and if answered before, I thank you for pointing to it.
DJI: I wonder if five rotors wouldn't be safer in case one fails, in terms of RTH and minimal flight control.

These would be my replies

1) A visual inspection before and after flight for any chips or cracks, but if you've not hit anything then they should be okay.
2) No, never lost a prop' in flight.
3)No, no motor failure.
4) It probably could, but maybe not much point (see 5 below).
5) No, any prop, motor, or ESC (Electronic Speed Controller) failure while flying means the aircraft will drop from the sky in an uncontrolled manner until it hits something below.
6) No RTH (See 5).
7)No (See 5).

The 'Industrial' platforms (6/8 motors) that DJI produce I believe have redundancy built in for one motor/prop failure.

I have had a motor go on a different quad (Gaui) and it went down. Fast.
I have had a bird strike on a hexacopter with half a prop gone, and the copter was flyable, albeit vibrating a lot, and it needed almost full power to stay in the sky.

simply put, a quad motor aircraft cannot sustain flight on three motors.

Cedric Pieterse Posted at 2017-1-17 12:21
I have had a motor go on a different quad (Gaui) and it went down. Fast.
I have had a bird strike on a hexacopter with half a prop gone, and the copter was flyable, albeit vibrating a lot, and it needed almost full power to stay in the sky.

so a hexa would at least have controlled descent. i guess thats the best setup for such occurrence. let's hope someone will come up with a real story, although p4 is fairly new.

WindSoul Posted at 2017-1-17 17:46
so a hexa would at least have controlled descent. i guess thats the best setup for such occurrence. let's hope someone will come up with a real story, although p4 is fairly new.

What do you mean by a real story, the answer has already been given that a quad motor aircraft will not decend under any sort of control with one motor failed or one prop missing. That means a P4. The minimum number of motors for a failsafe situation is 6.

AlecW Posted at 2017-1-17 11:12
A bird strike is enough to take out a prop and as Ardvark mentioned the flight path after losing a prop for any reason is pretty much vertical until something (like the ground) stops the drone.

i fail to see a bird strike because this thing doesnt move that fast and is pretty noisy. i did catch a gull veering away from the drone pretty sharply, also birds on the lake move off but kind of lazy, as they're getting used to the toy. i did fly like 1m above the water surface, but i wont recommend it cause of...bird strike. that was reckless though.
and my dog tried to lick the propellers while was hovering. it was like in a bad dream, happened so unexpected (steered the dog away several times and seemed to get the message), didnt even get time to yell or lift off. obviously she learned and i hope she wont forget, but for anyone with pets or kids around, i recommend be twice proactive rather than sorry once.

I've just had a Déjà vu moment

Geebax Posted at 2017-1-17 17:48
What do you mean by a real story, the answer has already been given that a quad motor aircraft will not decend under any sort of control with one motor failed or one prop missing. That means a P4. The minimum number of motors for a failsafe situation is 6.

yeah ok, got that part. i meant to hear from someone who got into such a thing. more details, like what happened and obviously what took to put the drone back in the air. since we're at it, wouldn't hurt to hear a real story.and forgive me but i believe the minimum number would be 5.

Aardvark Posted at 2017-1-17 18:02
I've just had a Déjà vu moment

you look pale. having flashbacks is a bit worrisome. may i recommend some real, fresh air? unless youre born and bred in the virtual world, case in which a bucket of bits never hurt.

Grizz 1 Posted at 2017-1-17 15:45
simply put, a quad motor aircraft cannot sustain flight on three motors.

a quad would have no reason to fall if balanced and with two opposing rotors running. is statically unstable ill give you that, but thats where the third rotor may play its role.
now dont be surprised if even with two opposed rotors, dynamic stability could be achieved while drone would enter auto-rotation. not same thing as a helicopter, but dynamically possible.

AlecW Posted at 2017-1-17 18:15
It's happened before.  And I just used it as an example, a quad copter will fly vertically downwards if for any reason one of the props stops.  It's basic physics.  

I have an idea for your 5th prop idea.  Put one of these on when you fly and you'll be just fine, I promise, nothing bad will happen.

nice cap. i guess that counts somehow as a contribution too. good job!

WindSoul Posted at 2017-1-17 18:37
a quad would have no reason to fall if balanced and with two opposing rotors running. is statically unstable ill give you that, but thats where the third rotor may play its role.
now dont be surprised if even with two opposed rotors, dynamic stability could be achieved while drone would enter auto-rotation. not same thing as a helicopter, but dynamically possible.

Drones do not do auto-rotation. You had better look up autorotation to get an insight on how it happens, because it requires variable pitch rotors in order to work. You are way out of your depth on this, just accept that a quad cannot recover from a single rotor loss.

Geebax Posted at 2017-1-17 18:40
Drones do not do auto-rotation. You had better look up autorotation to get an insight on how it happens, because it requires variable pitch rotors in order to work. You are way out of your depth on this, just accept that a quad cannot recover from a single rotor loss.

it s ok if you dont want to think it off. i only hoped you will try. what else? ah, good job!

I think what is being looked for is

Aardvark Posted at 2017-1-17 19:13
I think what is being looked for is This

amazing thank you.

Geebax Posted at 2017-1-17 18:40
Drones do not do auto-rotation. You had better look up autorotation to get an insight on how it happens, because it requires variable pitch rotors in order to work. You are way out of your depth on this, just accept that a quad cannot recover from a single rotor loss.

This is what I meant. Check the time 07:30 on the link.

Sorry I couldn't find it myself and fast enough to avoid the nonsense of your message

AlecW Posted at 2017-1-17 19:05
Much better idea than any of your "ideas".   Seriously, you think a 5th prop would help a quad stabilize in the event of a prop failure?

The right thing for you would be to accept your misdemeanour. There's a first in everything.
I didn't wear that hat because it didn't look new. You can have it back now. Enjoy!

WindSoul Posted at 2017-1-18 22:04
This is what I meant. Check the time 07:30 on the link.
It's a ted talk about quads
Sorry I couldn't find it myself and fast enough to avoid the nonsense of your message

Nonsense? That TED clip is as old as Moses, the aircraft was specifically programmed to fly like that, it was not a spontaneous action, and you may notice he trimmed two propellers diagonally oposite each other. Not anything like losing a single prop in flight, which is more like the scenario that would occur in the wild.

BTW, we would appreciate it if you replaced the 'Wind' in your username with an 'R'.....

The bottom line is that if any of the drive systems fails on a Phantom 4 then the aircraft will drop in an uncontrollable manner.

Geebax Posted at 2017-1-18 23:50
Nonsense? That TED clip is as old as Moses, the aircraft was specifically programmed to fly like that, it was not a spontaneous action, and you may notice he trimmed two propellers diagonally oposite each other. Not anything like losing a single prop in flight, which is more like the scenario that would occur in the wild.

BTW, we would appreciate it if you replaced the 'Wind' in your username with an 'R'.....

Geebax:

Not trying to rile the honeycomb, but:

Could the quad be programmed to compensate for the sudden loss of a single prop by "losing" the opposing prop, and thus losing yaw, but maintaining stability long enough for an emergency landing? After all, it would just be another failsafe "algorhythm..."

Keep Smiling,

Augustus

Geebax Posted at 2017-1-18 23:50
Nonsense? That TED clip is as old as Moses, the aircraft was specifically programmed to fly like that, it was not a spontaneous action, and you may notice he trimmed two propellers diagonally oposite each other. Not anything like losing a single prop in flight, which is more like the scenario that would occur in the wild.

BTW, we would appreciate it if you replaced the 'Wind' in your username with an 'R'.....

auto rotation is there, the clip is there and if you followed the thread someone even posted another clip where one propeller flies off.
for your information, auto-rotation is an inherent effect of a falling object. is a drag effect, meant to slow down the fall.

in case of helicopters, auto-rotation is a parachutal effect induced by the air turning the main rotor. happens only if main rotor shaft disconnects from engine and is released to interact freely with the air, as in the case of a gyrocopter.

in the case of a falling drone, no such gyrocopter effect can be observed. at least not a useful one. the auto-rotation in this case is a degree of freedom induced by cyclic changes in rotors speed. this controlled auto-rotation has no connection to the natural fall, but could greatly overachieve the slowing down effect of natural auto-rotation.
you're welcome.

im not here to fight arguments like "deep over your depth" or "we would appreciate". those combined with your rank reflect poorly on DJI. you only need help on how to behave in  public space, and I apologize if I failed you on that aspect.

Augustus Brian Posted at 2017-1-19 07:01
Geebax:

Not trying to rile the honeycomb, but:

you're asking questions to a guy who proved his worth in denying the evidence. let alone language and accountability. is your choice and i respect it.
i am not trying to substitute myself to your choice of answering. since anyone can contribute to this thread, please allow me to make a public contribution, which you are also wlecome to.

Not sure if a phantom could be controlled in a rotor fault. is too heavy. maybe a mavic. and definitely not by ejecting a prop. but you had my thoughts about whether a failsafe algorithm exists to support a controlled descent.
if you check msg 18. you could see the propeller is flown off axle. they simplified the experiment. if propeller stood there, then shutting down the motor and dealing with possible effects of auto-rotation of the downed rotor would have made the motion more random. hence less controllable.
in the clip i attached, they cut the blades on two propellers. is a different thing. even if motors shutdown, there will still be aerodynamic interference from chopped rotor blades. they even say full control is not possible, but partial control is achieved. what you can see clear as day is that the stability is dynamic (in both clips), the drone auto-rotates in order to retain some semblance of control.
i believe that if the rotors were powerful enough, even with three out of four rotors down, a partially controlled descent should be possible. but given the complex multi-axis auto-rotation induced by the algorithm meant to slow down the descent (makes me think of the movie "oblivion", where when they shot the drone she started spinning crazily before falling. they got the fact right), the high speed rotation of the drone would still make the crash damaging.
therefore the degree of control is achieved at the expense of auto-rotation, and saving the drone by accelerating its rotation becomes a limiting factor

i started the thread because i wanted to know what do i face in case of a rotor failure. in terms repair expenses. looks like there are no algorithms in place to shut down the rotor and slow down the descent of a P4 in this case.

i will leave to the character you addressed the message the honors of answering your questions. Capitaine, amuze us!

It sounds like you are trying to make a silk purse turned into a pigs ear. I fly Heli's and I can tell you that without a tail rotor,  There will be no control at all.
Auto rotation can only work if the AC has directional control.
Without it AC will just spin and fall to earth like a rock.
Negative pitch is what gives rotor it's speed. The spinning rotor acts like a Para shoot and helps produce drag to the fall.  At the last seconds of falling you give positive  pitch to blades and you have 2=4seconds to use the inertia gained in falling to land the craft.
I have seen vids showing a typhoon flying with one prop dead but that example will not fly with 4 props.
A helicopter, real or RC will not fly without tail rotor.  I have had belts break in flight and down comes the AC.   Even with working main rotor.
Rotary wing aircraft work on the same principle as fixed wing AC.  The rotor is a wing not a blower.  The props on Phantoms and all other DJI products are propellers, not wings.
There are para shoots for RC aircrafts  that open from a different signal, an add on to AC.  maybe this is what you need.  
There is nothing in common with either type of AC and never the twain shall meet.
Good luck turning your Phantom into a helicopter  {:4_177:}

Heres an addo on to my other post.
Center of gravity.......This is also a very important part of auto rotation.  You can't just stick a rotor anywhere you want. just like on a plane, the wings have to be located at the center of gravity.
If not.....It just won't happen...
I'm not sure what happens to the CG on a Phantom when a prop is lost but I'm pretty sure that it will be too out of balance to fly..

Odan Posted at 2017-1-19 08:57
It sounds like you are trying to make a silk purse turned into a pigs ear.  I fly Heli's and I can tell you that without a tail rotor,  There will be no control at all.
Auto rotation can only work if the AC has directional control.
Without it AC will just spin and fall to earth like a rock.

you yourself said Rotary wing aircraft work on the same principle as fixed wing AC.  The rotor is a wing not a blower
for a wing to create lift, only needs motion through the air. as long as the main rotor turns, there is lift to counter the weight. yes, the body may counter rotate but if the rotor is at speed, then you only need to load it before impact. that way the counter rotation is maintained minimal throughout descent.

heli auto-rotation is not a walk in the park. is the ultimate attempt to save the lives of people onboard. forget the damage to machine.

also blowers dont fly. see you jumping. those flying are ducted, they're called jets. i guess that's not common knowledge among fliers like yourself. the propellers of p4 are rotors, not blowers. and stop hitting yourself in the head in public, is not funny.

AlecW Posted at 2017-1-19 09:14
Bottom line, if a prop stops for any reason the current phantoms will come down like rocks.

i see some common sense at last. far from fixing or even recognizing yourself, but is a good start.

Odan Posted at 2017-1-19 09:15
Heres an addo on to my other post.
Center of gravity.......This is also a very important part of auto rotation.  You can't just stick a rotor anywhere you want. just like on a plane, the wings have to be located at the center of gravity.
If not.....It just won't happen...

just make an effort to at least check the vids posted in this thread, if not the topic in discussion. just  saying things to contradict evidence posted in the thread doesn't do anyone any good. you're smoking in a public space. good thing the space is virtual, that clears the air (not around you)

AlecW Posted at 2017-1-19 09:50
Not sure what you are saying, am I wrong?

you're doing fine for now. just not using the right tense at asking the question. but this is off-topic, so i'll settle at leaving where it is. thread is solved anyway

AlecW Posted at 2017-1-19 10:08
You've lost me.  Are you trying to say with some programming a phantom could be made to land with less than 3 props running?

cant say that. dont have the means to test it but even if, i doubt i would be able to develop the algorithm. ill keep you posted though, im only in the initial phases and working with arduino might prove too slow to get me anywere. time is also an expensive commodity for me.
what i'm saying is you owe some apologies to all readers of this thread for your misdemeanors. doesn't matter to me, but to you it does. it will reflect on the way people will interact with you in the future.

AlecW Posted at 2017-1-19 09:14
Bottom line, if a prop stops for any reason the current phantoms will come down like rocks.

That is incorrect, the aerodynamics are completely different to those of a rock and the density very different to most rocks.

From what I have seen, it appears that a Phantom which has lost power will land at about 18mph vertical speed.  If it only looses 1 motor then I think it still comes down at about the same speed because it cant put much power into the others without making itself unstable.  Not sure what happens when it looses a prop, doesn't seem to happen very often, but I suspect that it will still land at close to 18mph vertical speed.

If you are trying to work out why, remember that the props rotational axis are not vertical so if you loose one then it's partner will put the aircraft into a spin.

Funny thing happened to me this morning, a red tailed hawk was stalking my low flying Phantom. Once it realized the noisy thing wasn't food it flew away without incident.