rapid descent... (is it a recipe for disast...)

[vandemonian]

Hi all,

I'm curious (possibly worried) about making "full-stick control" during descents on my A2S.. (Mode 2)
To make a descent by apply backward input on the left (throttle) stick works as expected, but if I pull back to max position to accelerate the rate of descent, I'm also using the same "stick-input" that is also a "stop motor" command (land) - so, I'm concerned about using full "down" and having the motors just stop because its also the "shutdown" command.. or is it only a "shutdown" once its in "home" or ground proximity and differs from the CSC "shutdown" which pulls the pin and lets it drop?
I don't want to test it with a full stick command and have to run towards a drone that's shut down the motors at 10+M alltitude and try to catch it!

 

[Kilrah]

It only stops motors if you have full down and the aircraft it is not descending anymore, since if that's the case it means it's on the ground.

 

[old man mavic]

@vandemonian @Kilrah beat me to it
the quickest way to descend from height , is to fly forwards ,with full down stick ,rather like an aircraft comes in to land on the glide path if the landing area is surrounded by trees for example then you can turn as you descend as well

 

[vandemonian]

It only stops motors if you have full down and the aircraft it is not descending anymore, since if that's the case it means it's on the ground.

Thanks, that makes sense to me too.. I just didn't know what the IF statement was.
Full stick down = max descent IF descending
Full stick down = land / shutdown IF no longer descending.

 

[vandemonian]

@vandemonian @Kilrah beat me to it
the quickest way to descend from height , is to fly forwards ,with full down stick ,rather like an aircraft comes in to land on the glide path if the landing area is surrounded by trees for example then you can turn as you descend as well

Thanks, I do that - making tight spirals as rapidly down as I dare with the throttle.. I just didn't want a mid air shutdown by over-controlling the down input.

Thanks again..

 

[Deleted member 103366]

If the response to the CSC position is set to "Emergency Only" and the CSC position is used whilst the drone is flying, the drone will only stop the motors in mid air if the drone 'thinks' it has suffered an emergency. page 42 of the manual.
BUT be warned, it would be as well to check that the response is set to "Emergency Only" before deliberately using that position. It should be, it is the default. But if, by any chance, the response is set to "Anytime" the motors are likely to stop in mid air if the CSC position in held for more than 2 seconds, I think the actual 'delay' is around either 0.7 seconds or 1.7 seconds.
If you do a search in here for "fell from the sky" you may find two recent threads were it looks as if the drones did stop their motors in midair because the CSC response was set to "Anytime".
I have tested both settings with a Mavic Mini, in the test of "Emergency Only" I sent the drone up to 100m+. I then put drone in Cine flight mode (the slowest flight speed mode) and put the sticks in the CSC position and held them there. The drone descended under full control in a helix and even slowed its descent as it approached the ground. When I released the sticks the drone hovered.
In the "Anytime" test I started the CSC position with the drone between 6ft and 8ft off the ground, the motors stopped when the drone was about 18" off the ground, it fell onto soft grass.
I would suggest you try your shot with the drone in cine mode, N or S mode may be a bit wild.

I am afraid I would be surprised if lateral movement increases the descent speed BUT, looking at the specs for the Air 2s, if the drone is being commanded to descend at maximum speed in N or S mode it is probably sensible to add lateral movement to the descent. The reason being, with descent speeds of 6m/s a pure vertical descent In windless conditions is likely to have the drone descend into its own prop wash which makes for a rough ride if nothing else, google "vortex ring state", moving laterally means the drone will be descending into 'cleaner' air.

 

[vindibona1]

Don't you need the sticks to be down and together (or apart?) to shut the motors off, not just both straight back?

 

[Deleted member 103366]

Don't you need the sticks to be down and together (or apart?) to shut the motors off, not just both straight back?

Correct but Vandemonian does mention the CSC and doing "tight" (descending) "spirals" which, in the default stick mode, would entail the left stick being down & in/out and the right stick in/out & up/down.

 

[vindibona1]

Correct but Vandemonian does mention the CSC and doing "tight" (descending) "spirals" which, in the default stick mode, would entail the left stick being down & in/out and the right stick in/out & up/down.

Thanks for the clarification. Is there a way to turn off the emergency motor stop function temporarily?

 

[Deleted member 103366]

Strictly speak NO but in effect the default setting, "Emergency Only", does just that.
Conversely a mid air motor stop is all too easy to trigger if the response is set to "anytime ".

 

[vandemonian]

Thanks again for answers and awesome testing of the idea.. It makes sense that a "full control input" should not trigger an unintended result even if that corresponds (in possibly different conditions) to another response without an existing menu safety check and that's what the preset "Emergency" condition provides. PhiliusFoggg chimed in with great understanding and advice. As to Vortex Ring State.. I have read reasonably widely during my time with cyclic-collective control flying and know that its a fast way to meet the ground.. fascinating stuff but really that's "Big State" air conditions but remarkably you can experience relative "air-mass" influences if you fly indoors... try it and notice as soon as you get in relative proximity to a hard ceiling how quickly you get sucked to the ceiling.. like a reverse "ground-effect"

 

[Meta4]

Thanks again for answers and awesome testing of the idea.. It makes sense that a "full control input" should not trigger an unintended result even if that corresponds (in possibly different conditions) to another response without an existing menu safety check and that's what the preset "Emergency" condition provides. PhiliusFoggg chimed in with great understanding and advice.

Some of the replies might have confused you.
You asked about descending by pulling the left stick down, but much of the discussion that followed was about CSC which is completely different (that's the one that emergency/any time applies to.

You can safely descend at full left stick down.
It's completely safe and there's no need to spiral down.
Left stick down won't kill the motors until the drone has come to rest and can't descend any further.
DJI would not have designed the common descent method to kill the motors in flight.
But if they did, there would be a big section about it in the manual

As to Vortex Ring State..

VRS is a thing of the past for DJI drones.
Look at the motors and you'll note that they are not aligned vertically, but are offset a few degrees.
Together with the limited descent speed has eliminated VRS as a concern for DJI flyers.
You can safely descend full left stick down from hundreds of feet up without any worries.

 

[Deleted member 103366]

With regard to rapid, pure vertical descents, it's not an easy thing to check visually (meaning eyes on the drone) with some magics e.g. the Mini's and perhaps Mavic 2 P/Z's as they automatically slow there descent as they get near the ground.
But, from memory, with a Phantom 3 you can descend at full speed until the drone is very near the ground or hits it.
I have watched more than one Phantom 3 "close up" whilst they were in a rapid, vertical descent and they definitely wobble much more than when they in a slow vertical descent.

With your MA2s and on a windless day it might be interesting to do a rapid, vertical descent at height, say from 350ft to just above VPS range and then climb back up to 350ft and do an appreciably slower, vertical descent, then climb back up to 350ft and do a rapid descent whilst also movingthex drone horizontally. Then look at the logs and see how much the drone wobbled during those descents.
I am not flying at the moment otherwise I would test it myself.
Putting the gimbal in FPV mode during the first two descents might be interesting too.

By way of explanation for the FPV suggestion.
When I did the mid air motor stop and restart with the Phantom 3 I was watching the phone's screen during its descent. The drone appeared to be descending in a flat spin, it was only when I looked at the logs that I realised how much the drone had actually wobbled during the free fall and how good a job the gimbal did at smoothing out those wobbles.
Yes I realise a free fall is an entirely different situation from an under control rapid descent, I cite the free fall to demonstrate how much the gimbal can, in the non FPV mode, smooth out the video.