Ground clearance question - avoiding smash landing?

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Hi all,

This question has probably been asked but I cannot find it specifically to my question in a search.

Let's say I take off to 15ft (so the DJI app shows take off at 0 ft, and I climb to 15 ft). I am aware this drone does not a have a ground-proximity warning, like an aircraft. That said, let's say at 15 ft I fly a horizontally, but up a gradual slope. If I understand correctly, let's say at some point I will be only 8 ft above the ground, but my heigth reading will remain at 15ft. Is that correct?

Next, at that point when I'm really only 8 ft above the ground, I tap the "down" button for an automatic landing (not the RTH). Will the drone smash into the ground since it thought it was 15 ft above ground, but was really only 8? I use those numbers as examples only, more concerned if I take off to a height of 30 ft, and go up a slope where the actual height above round is less. I know I can do a manual landing, but if I want the drone to land in a nearby empty field and I don't know it's altitude relative to the 0 ft at take off, I don't want it to hit the ground hard when landing automatically if it thinks it's higher above ground than it really is.

Or is it's rate of descent such that when it touches down at whatever altitude above starting point 0 ft, the descent speed is slow enough that it won't land too hard regardless? Thanks for responses and suggestions!
 
The drones knows when it has touched down by using the IMU and the barometric sensor so it wont thump into the ground.

They are quite 'smart' in that respect

:)
 
I don't want it to hit the ground hard when landing automatically if it thinks it's higher above ground than it really is.
Just like a real plane, the Phantom doesn't have to land at the same place and elevation as where it took off.
If you choose to auto land, when it's descending to land, it will descend until it can descend no further.
 
Does that mean it will descend at a rate that won't hit the ground too hard, regardless of where I try to land and at whatever altitude it starts the descent?
 
yes, its decent speed is slow enough to land from when you autoland but if you descend manually with full stick down you will hit the ground with a thump
 
my first rth landing yesterday stopped 2-3 inches and then settled to ground. I'm with your thinking, if it thinks ground is 40 ft down, it is not going to be creeping up on it.
 
The drones knows when it has touched down by using the IMU and the barometric sensor so it wont thump into the ground.

They are quite 'smart' in that respect

:)

so it is using the ground effect prop wash to detect ground is close? Becasue that is the only thing that would change barometric pressure. Air density at ground level at 40 ft above you, would be same as air density 40 ft above the ground. Otherwise you could breath on top of Mt Everest..
 
so it is using the ground effect prop wash to detect ground is close? Becasue that is the only thing that would change barometric pressure. Air density at ground level at 40 ft above you, would be same as air density 40 ft above the ground. Otherwise you could breath on top of Mt Everest..


you would have to delve into the P3s operating system to find that out. I think it is more the IMU and the autoland descent speed
 
you would have to delve into the P3s operating system to find that out. I think it is more the IMU and the autoland descent speed
I would LOVE to do that. But DJI is making it very difficult. With access to it, you could add second camera for 3D pictures. Let proximity sensors stop RTH(suicide) flights. Even add a parachute deployment.
 
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I would LOVE to do that. But DJI is making it very difficult. With access to it, you could add second camera for 3D pictures. Let proximity sensors stop RTH(suicide) flights. Even add a parachute deployment.


we have root access so just about anything is possible for a skilled Unix system engineer :)


And I believe they do have a Software Developers Kit available
 
we have root access so just about anything is possible for a skilled Unix system engineer :)


And I believe they do have a Software Developers Kit available
They do? I will have to get it I guess. Been learning sysV file systems since I ordered the drone. From the hacks I read they changed the root password in 1.6 update so you couldn't enable shell anymore.
I would think the sdk would be for writing the app, but maybe it requires NDA, and $$$ for it is why the hackers don't.
 
They do? I will have to get it I guess. Been learning sysV file systems since I ordered the drone. From the hacks I read they changed the root password in 1.6 update so you couldn't enable shell anymore.
I would think the sdk would be for writing the app, but maybe it requires NDA, and $$$ for it is why the hackers don't.

They didn't change the password , I am on 1.70.90 and still have ftp and telnet access
 
so it is using the ground effect prop wash to detect ground is close? Becasue that is the only thing that would change barometric pressure. Air density at ground level at 40 ft above you, would be same as air density 40 ft above the ground. Otherwise you could breath on top of Mt Everest..
Not so, the barometric pressure sensor is much more sensitive than that. A few feet at most.
 
Part of the OP made me wonder. I live at sea level, some areas near here are below sea level and having never flown from a much heigher relative height I hadn't noticed about the takeoff point being 0 ft.
The destructions do say max service ceiling is 6000m, so assume that's for the barometer side of things.
 
so it is using the ground effect prop wash to detect ground is close? Becasue that is the only thing that would change barometric pressure. Air density at ground level at 40 ft above you, would be same as air density 40 ft above the ground. Otherwise you could breath on top of Mt Everest..
I have thought this for some time. My Standard teds to "bounce" just a bit before it reaches the ground, I always attributed that to the increase in air pressure from the props getting close to the ground.
 
The destructions do say max service ceiling is 6000m, so assume that's for the barometer side of things.

The dynamic range of the baro has never been published or determined AFAIK.

The operating ceiling is more likely due to air-density.
 

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