I'm concerned about rapidly descending from high altitude.  If I hold the left stick down for more than 3 seconds while in flight, will the motors turn off?  I don't want that to happen while in flight.  The manual is unclear as it says after the aircraft has landed hold the stick down for 3 seconds to shut off the motor.

Do you think that people clever enough to create the Phantom would make the normal method of descending kill the motors .... and not mention that in the manual?
DJI design engineers are very clever.
You can hold the left stick had down for as long as you like in flight and all that happens will be the drone descends.
The Phantom has to know that it has landed before left stick down will kill the motors.

Labroides Posted at 2018-5-10 21:53
Do you think that people clever enough to create the Phantom would make the normal method of descending kill the motors .... and not mention that in the manual?
DJI design engineers are very clever.
You can hold the left stick had down for as long as you like in flight and all that happens will be the drone descends.

The engineers are good.  There are several items in the manual that could be improved.

If the drone senses the resistance of the ground then the downward stick will kill the engine. If you grab the drone out of the sky and press the left stick down it will shut off also.

I always lock the left stick down when I hear aircraft even coming close to where I am.  Can drop 100 ft in a hurry.  Trick is to know how low you can go and stay above everything.

The DJI drone will not quit until the VPS kicks in at 3' AGL and then only once it is at ground level. You can descend as fast as you want. It will not fall from the sky.

I believe it relies on a combination of VPS, sonar, and stoppage in vertical movement to decide if 3 seconds of full sticks down needs to shut down the motor. So like everyone said, you should be safe.

I, however, almost always leave myself a bit of room before reaching full left stick down. Mostly habit.

All good information.  Thanks!!

Last but not least, if you want the fastest descent (and maybe because of running out of battery), you can do a CSC to enter a free fall, then restart motor before it reaches the ground. Disclaimer: not tried this myself.

rent Posted at 2018-5-12 18:44
Last but not least, if you want the fastest descent (and maybe because of running out of battery), you can do a CSC to enter a free fall, then restart motor before it reaches the ground. Disclaimer: not tried this myself.

No, but others have tried it and it does not work. Please don't suggest such drastic actions you have not tested.

Works on the Mavic ;) and the Phantom 4 Pro

Bashy Posted at 2018-5-12 19:25
Works on the Mavic ;) and the Phantom 4 Pro

More accurate to say that it sometimes works!
You need 400ft or more to restart a Phantom and even then it may not arrive back down the right way up.

However sports mode will give you some extra descent speed if you want to come down fast, just remember that there is no obstacle detection so you have to stop before it hits the ground.

Geebax Posted at 2018-5-12 19:08
No, but others have tried it and it does not work. Please don't suggest such drastic actions you have not tested.

Nigel_ Posted at 2018-5-12 23:14
More accurate to say that it sometimes works!
You need 400ft or more to restart a Phantom and even then it may not arrive back down the right way up.

OP did say high altitude

Why would it only sometimes work? it should work all the time if they are high enough and your reaction time is fast enough, a lot of cafuffle and panic would reduce said height, but, if at high altitude then you have time to spare, as to the reasons of being at high altitude is beyond me though, unless of course one is classing 120m (400 feet in mickey mouse money) then a) thats not high alt and b) i would be surprised if it had time to do the CSC then restart motors in time before terra firma took hold. having said this....

In the video below, they took it to 300m, did CSC, they let it drop 100m and restarted motors, it dropped a further 66m est. before it stabilised so, being realistic, it can be done with a Phantom from 400ft as long as its not done below 400ft, need a wee saftey margin ;) no chance i would be testing this, YT testing is good enough for me lol

Skip to 1:14

Bashy Posted at 2018-5-13 20:10
OP did say high altitude

Why would it only sometimes work? it should work all the time if they are high enough and your reaction time is fast enough, a lot of cafuffle and panic would reduce said height, but, if at high altitude then you have time to spare, as to the reasons of being at high altitude is beyond me though, unless of course one is classing 120m (400 feet in mickey mouse money) then a) thats not high alt and b) i would be surprised if it had time to do the CSC then restart motors in time before terra firma took hold. having said this....

It only takes one small issue to extend the start up and initialisation time and you just made a divot in the ground. And any delay on the part of the operator, indecision or panic and it is history. You guys can do it all you like, but I guarantee I will never use the procedure.

BTW, those guys in your video did not appear to care what happend to their P4, whereas I would be more cautious.

Geebax Posted at 2018-5-13 20:41
It only takes one small issue to extend the start up and initialisation time and you just made a divot in the ground. And any delay on the part of the operator, indecision or panic and it is history. You guys can do it all you like, but I guarantee I will never use the procedure.

BTW, those guys in your video did not appear to care what happend to their P4, whereas I would be more cautious.

I only replied because you said it does not work, yet i had seen these videos prior so i knew that it can be done and I did state that, by saying "a lot of cafuffle and panic would reduce said height"

I am only showing that it can be done, i wont be doing it thats for sure, i struggled with going under a bridge for gods sake no chance will i try this lol

Bashy Posted at 2018-5-13 20:58
I only replied because you said it does not work, yet i had seen these videos prior so i knew that it can be done and I did state that, by saying "a lot of cafuffle and panic would reduce said height"

I am only showing that it can be done, i wont be doing it thats for sure, i struggled with going under a bridge for gods sake no chance will i try this lol

Yeah, I noted that.

Bashy Posted at 2018-5-13 20:10
In the video below, they took it to 300m, did CSC, they let it drop 100m and restarted motors, it dropped a further 66m est. before it stabilised so, being realistic, it can be done with a Phantom from 400ft as long as its not done below 400ft, need a wee saftey margin ;)

Your maths doesn't quite work, the 100m + 66m = 166m which is more than 400ft.

The 100m drop gives time for the props to spin up backwards and the aircraft itself to start spinning, the gyroscopic forces and drag from the spinning props then stabilises the drop and ensures that the aircraft is vertical, which then means restarting the motors is likely to be successful.  If you start them earlier, before the aircraft is stabilised then it may end up tumbling to the ground, or even flying into the ground upside down.  

Based on doing it in the simulator, 400ft is the absolute minimum and requires an immediate restart before the aircraft starts to tumble.

In real life an upside down P4 with the props already turning can correct itself in 10ft, so it is a bit puzzling why we see some videos where a rapidly dropping P4 takes 66m, there are clearly some problems with stability when rapidly dropping, maybe due to flying in it's own prop wash, add a bit of wind and the results are random.

Given that most of us fly with a 400ft limit, it is not something to recommend.

Nigel_ Posted at 2018-5-13 23:37
Your maths doesn't quite work, the 100m + 66m = 166m which is more than 400ft.

The 100m drop gives time for the props to spin up backwards and the aircraft itself to start spinning, the gyroscopic forces and drag from the spinning props then stabilises the drop and ensures that the aircraft is vertical, which then means restarting the motors is likely to be successful.  If you start them earlier, before the aircraft is stabilised then it may end up tumbling to the ground, or even flying into the ground upside down.  

From the description, didn't watch the video, the motors get shut at 300m, started again at 200m and AC was stable again at 134m.
From that numbers it should be safe to do an shut/restart from 100m as it won't have accelerated 100m before restarting the motors.

Not gonna test this either, but in a matter of emergency it should be done.