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rapid decent
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cmmettler
lvl.2

United States
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Got my P3P Friday. after a few low altitued shake down flights, I took it up to 400' this morning. The question is....
If I pull the left stick all the way back for a rapid decent, will it shut the motors down, like when its on the ground ?

So far she flies great !
2015-6-7
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Total
First Officer
Flight distance : 336480 ft
Canada
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I have done the left stick down  for rapid decent , a few times . The phantom never shut off ...
2015-6-7
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dbeck
Second Officer

United States
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What is the reason for rapid decent?  Are you experimenting?  Possibly of MAJOR disruption of air air and unstable flying conditions! (Vortex Ring State) So the question is WHY do it?  And no it will not shut the motors down
2015-6-7
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cmmettler
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dbeck@promobox. Posted at 2015-6-8 07:52
What is the reason for rapid decent?  Are you experimenting?  Possibly of MAJOR disruption of air ai ...

Just experimenting. Good to know about the disruption of air. I wont try it.
Thanks
2015-6-7
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dbeck
Second Officer

United States
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If you do, start WAY high up, so if you do loose it, you have airspace to recover.  Nasty crash if you don't! VRS (Vortex Ring State) affects ALL real (and toy) helicoptrers/drones. It has only happened to me once, andf its scary. Total loss of control!
2015-6-7
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Victor7k
lvl.2

Canada
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So if I push the left stick down, it stops the motors only when the phantom is on the ground... If I push both control sticks down then the motors will stop.
2015-6-7
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dbeck
Second Officer

United States
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Yes on the first one. No on the second.  IF, you need to stop the motors while in flight (emergency ) then BOTH sticks to the center and down (CSC, like when starting the motors) that will the kill the motors in flight.  Built in safety  bailiout
2015-6-7
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Total
First Officer
Flight distance : 336480 ft
Canada
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One time I had a flock of geese sneak up on me  , until it was almost to late ....
2015-6-7
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Abe
Second Officer
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It will not shut off with full stick down unless it's on or very near the ground. The speed of descent is limited by the firmware to minimize the likelihood of vortex effect. I do full stick descents all the time and have never had a problem with P2V+, P3P and Inspire. No reason for concern.
2015-6-7
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dbeck
Second Officer

United States
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Well you go right ahead with what Abe says and pay no attention to what others here have said..in effect.."full throttle descents' are a recipe for disaster, sooner or later. But please by all means, let your own experience dictate your decisions
2015-6-7
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PhantomHelp.com
Captain
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Holding the left stick down will only shut the motors off when the Phantom stops descending. It does not matter how far you are from the ground.





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2015-6-7
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lightpanther
lvl.4

United States
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PhantomHelp.com Posted at 2015-6-8 09:55
Holding the left stick down will only shut the motors off when the Phantom stops descending. It does ...

How exactly is the P3 detecting that it is not on the ground, so as not to shut down if the left stick is pulled back all the way? Is it using VPS or is it using GPS?
2015-6-7
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dbeck
Second Officer

United States
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PhantomHelp.com Posted at 2015-6-8 09:55
Holding the left stick down will only shut the motors off when the Phantom stops descending. It does ...

Sorry, I have never, ever heard about this.  Do you have evidence? Ed Tahoe what say you?  This is news to me
2015-6-7
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Abe
Second Officer
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lightpanther Posted at 2015-6-8 10:09
How exactly is the P3 detecting that it is not on the ground, so as not to shut down if the left s ...

Without looking at the source code of the firmware, only DJI knows for sure. But from everything I've read, it uses a barometer and VPS to measure height. GPS is used to maintain forward/backward/sideways position. That's why in ATTi mode the Phantom will maintain altitude but will drift with the wind due to lack of GPS.
2015-6-7
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myhondas
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United States
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dbeck@promobox. Posted at 2015-6-8 08:13
If you do, start WAY high up, so if you do loose it, you have airspace to recover.  Nasty crash if y ...

From what I have gathered, it is really hard to put the P3P into a VRS state. They purposely tilted the motors  to help avoid it. Now the P1, P2, P2v+ can all enter and with prop guards on it is even easier to do. I have put guards on mine and did a number of rapid descents without any sign of it entering vrs state.
2015-6-7
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dbeck
Second Officer

United States
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Not my experience at all. I have a Inspire, and a PT2V 3.0 and have a P3.  On the second flight, I was not paying attention, to what I was doing and the batt fall to below 30%, I cranked the left stick down to hasten a quick landing and totally forgot about VRS, well I almost dumped it, I lived to tell about it!
2015-6-7
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Victor7k
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Canada
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dbeck@promobox. Posted at 2015-6-8 10:36
Not my experience at all. I have a Inspire, and a PT2V 3.0 and have a P3.  On the second flight, I w ...

What's VRS ???
2015-6-7
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dbeck
Second Officer

United States
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Vortex Ring State...in essence...dirty air.  Go google it, real helicopters can experience the same thing
2015-6-7
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Abe
Second Officer
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dbeck@promobox. Posted at 2015-6-8 10:36
Not my experience at all. I have a Inspire, and a PT2V 3.0 and have a P3.  On the second flight, I w ...

I don't doubt your experience, Dbeck. But if you fly enough something unexplainable can happen to virtually any movement you make at some point. It's the nature of complex systems. That doesn't make it the norm. I had a flyaway after losing signal once, but I don't expect that to happen every time, or maybe ever again. And I've lost signal many times since without a flyaway.
2015-6-7
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Mark97564
Second Officer
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United States
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The p3 is limited to 3 meter per second decent rate to avoid the vortex issue and it uses its barometer, vision positioning system and gps to know its not on the ground..  Now if you do csc like you do to start the motors they will stop no matter how high you are
2015-6-7
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labroides
Captain
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Australia
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dbeck@promobox. Posted at 2015-6-8 09:45
Well you go right ahead with what Abe says and pay no attention to what others here have said..in ef ...

And you go ahead and pay no attention to those who speak from experience with full throttle descents.
They are quite safe to execute.
For someone that didn't realise that the left stick down only stops the motors when the Phantom has stopped descending, you speak with great authority.
2015-6-7
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giant
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labroides@yahoo Posted at 2015-6-8 14:21
And you go ahead and pay no attention to those who speak from experience with full throttle descen ...

Well spoken :-)
2015-6-8
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aburkefl
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lightpanther Posted at 2015-6-8 10:09
How exactly is the P3 detecting that it is not on the ground, so as not to shut down if the left s ...

In many of its modes (even when not using GPS) it's still using barometric pressure to identify it's further off the ground than when you started.

I think it's been confirmed several times already by DJI "spokes-people" that pulling the throttle all the way back will not shut motors off if it's still in the air.
2015-6-8
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aburkefl
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labroides@yahoo Posted at 2015-6-8 14:21
And you go ahead and pay no attention to those who speak from experience with full throttle descen ...

"And in this corner, weighing in at...."

Some of this has actually become funny. Personally, I like the comment from one poster - "...just because something *could* happen doesn't mean it will. I'm not the most experienced quad pilot here, but I own four quads (including a new P3P) and I've never experienced anything remotely akin to VRS. That said, I don't think I've had much in the way of emergency landings either. I'm apparently much more conservative in both my battery usage and flying height/distance. I figure it's hard to crash a car at 150 mph if you never go that fast!

Despite the once-in-a-while jerks who show up here and the plethora of complainers (I think it's the same people over and over again) I still enjoy the dialog I see here. I know I've learned a lot.

The first little flying thingie I saw was some kind of miniature helicopter that was designed to fly indoors. It was far too tiny and light to fly in any but the lightest breeze - the A/C vents probably provide a hurricane-scale wind! It was one of those Billy Mays-type ads "...call now and we'll throw in another copter..." Boy am I glad I never bought one of those things.

Can you imagine Ronco selling a drone on TV? LOL
2015-6-8
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labroides
Captain
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Back in the early P2 days when they could descend at 6 metres/sec, the potential for VRS was real and it was necessary to descend with some forward motion if coming down fast.
To make things safer for newbies, DJI limited the descent speed back to a snail's pace 2 m/sec which prevented VRS being an issue.
The P3 has offset motors as another anti-VRS feature and descent has been bumped up to 3 m/sec.
Full speed descents in the P2 and P3 are quite safe - (at least without prop guards that is).
2015-6-8
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lightpanther
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labroides@yahoo Posted at 2015-6-8 22:15
Back in the early P2 days when they could descend at 6 metres/sec, the potential for VRS was real an ...

But seriously, how sophisticated is the barometer in a Phantom, if it has one? And what would be its level of accuracy? It's not a weather station. It would make more sense to me that the Phantom uses GPS for the fact that the left stick is right down but the Phantom hasn't descended at all for 3 seconds, to cut the motor.
2015-6-8
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col.lloyd
lvl.4
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United Kingdom
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Barometers are more accurate than GPS for altitude.
2015-6-8
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labroides
Captain
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"But seriously, how sophisticated is the barometer in a Phantom, if it has one? And what would be its level of accuracy?"

Look it up.  GPS is great for horizontal position but woeful for altitude.
It can easily be out by 100 feet or more.
The Phantom uses a barometric sensor for relative altitude and it's accurate to within a couple of inches - that's how your Phantom maintains altitude in hover.
2015-6-9
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Fulgerite
First Officer

United States
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So... descending vertically on a rotor craft means you are flying into your own turbulence.  This happens to ALL rotorcraft.  Many people have been killed in helicopters by descending to fast into their own turbulent air causing a stall condition that is not recoverable.   (Known as Vortex Ring State)



This type of stall happens to DJI Phantom quads as well.  The vortex ring state can be avoided by maintaining forward flight while descending.  In other words... Don't sit still and descend... Fly forward or sideways while descending and you will not experience a vortex ring state.

Many people have complained that the Phantom 3 has a more limited rate of descent vs previous Phantoms...  The reason DJI has slowed the maximum vertical descent rate is to avoid vortex ring state stalls & crashes.  Just avoid sitting still while descending rapidly and you can avoid the problem.
2015-6-9
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isaache
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Spain
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col.lloyd@mac.c Posted at 2015-6-9 02:43
Barometers are more accurate than GPS for altitude.

Not correct, barometers are more precise than GNSS but GNSS is more accurate than barometers as does not suffer drift caused by the variation of the environmental pressure. From navigation point of view an Extended Kalman filter would be ideal to merge the data from both "sensors" and provide the best of both worlds.

Isaac
2015-6-9
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col.lloyd
lvl.4
Flight distance : 286637 ft
United Kingdom
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That depends. The Phantom knows it's on the ground at startup, surely it can use that pressure as a datum. (QFE) In that case, baro will be more accurate than gps.
2015-6-9
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jbrazda
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dbeck@promobox. Posted at 2015-6-8 09:45
Well you go right ahead with what Abe says and pay no attention to what others here have said..in ef ...

I do it every time I fly.  And Will continue to do it.
2015-6-9
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labroides
Captain
Flight distance : 9991457 ft
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Prop guards catch the wind like sails.
They slow your Phantom and give you less time per battery.
They get in the frame when you're filming.
They give some people a sense of security.
By reducing the power and effectiveness of the propulsion system they made it easier to get into VRS in the older Phantoms.
2015-6-10
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clkilljoy1
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labroides@yahoo Posted at 2015-6-10 21:36
Prop guards catch the wind like sails.
They slow your Phantom and give you less time per battery.
Th ...

My P2 crashed from VRS (dirty prop wash).  Classic total los of control.  With my P3 I am still cautious when descending.  Simple terms you push all the air out from under the copter and have no air to push against to give you lift.
2015-6-10
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buzzcbr
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lightpanther Posted at 2015-6-8 10:09
How exactly is the P3 detecting that it is not on the ground, so as not to shut down if the left s ...

With the left stick down ,when the P3 detects its not descending for more than 3 seconds it shuts the motors off
2015-6-10
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lightpanther
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buzzcbr@gmail.c Posted at 2015-6-11 00:44
With the left stick down ,when the P3 detects its not descending for more than 3 seconds it shuts  ...

Yes, but how does it "detect that it is not descending" - that is my question?
2015-6-11
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labroides
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lightpanther Posted at 2015-6-12 08:57
Yes, but how does it "detect that it is not descending" - that is my question?

With the barometric altimeter.
When the flight controller senses that the altitude hasn't changed despite throttle down.
2015-6-11
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chas3
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So the question is, if you took off from a rooftop deck, and wanted to descent quickly to a location lower than that rooftop deck, would the motors shut off if you held the throttle all the way down for more than 3 seconds?

And in the reverse direction - would the copter be smart enough to shut off if you took off from the ground and landed on a rooftop deck?
2016-6-10
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Kneepuck
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chas3 Posted at 2016-6-10 15:14
So the question is, if you took off from a rooftop deck, and wanted to descent quickly to a location ...

I usually land by hand catching my Phantom in the air.  It does not care. The barometric altimeter is sensitive enough to know that it is no longer descending,  and after 3 seconds of left stick down it shuts off.  I have also taken off and landed at altitudes a lot lower and a lot higher than take off point.  It still shuts down fine with full left stick down for 3 seconds.
2016-6-10
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labroides
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chas3 Posted at 2016-6-11 08:14
So the question is, if you took off from a rooftop deck, and wanted to descent quickly to a location ...

Higher or lower than takeoff point makes no difference, your Phantom can land anywhere ... just like a real plane.
Left stick down will never shut down your motors in flight .. only after the Phantom has landed.
2016-6-10
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