Hi all,
New pilot here looking for some clarification. I learned a valuable lesson today - not to fly the Mavic unless it has excellent GPS signal. I've flown some various RC devices and toy drones and am a fixed wing Private Pilot, but I'm not prepared to fly without assistance from the cpu's. Before someone tells me off for not knowing how to fly in ATTI, the forums are clear you cannot turn off GPS and I have no way to practice. I am in Greece on holiday and late last night came across a beautiful 1000 year old church in the middle of a city square. Flying in an open space where there were no cars or people I was hoping to get a nice vertical pan (straight up then straight back down to land) showing it situated in the heart of a congested city block but the Mavic was picking up only a few satellites (fluctuating between 3 and 7). I tentatively lifted off to test its stability in a hover just above the ground. It was drifting and behaved like it was on ice, responding to my control inputs but continuing as if with substantial momentum in any direction. I've experienced this with other RC drones but not with the Mavic. It took me about fifteen seconds to be convinced it was not going to stabilize and that I was not going to take any risks (to the drone or to any property around me). Unfortunately, the decision to land is where the difficulty began. I held the left stick down 100% (stick mode 2) and the Mavic descended until it made contact with the ground. The rotors continued turning and the Mavic skittered sideways turning slightly then without any change in throttle position (I was still holding the throttle 100% down) it lifted off and accelerated sideways and backwards colliding with a low wall. I was lucky, the crash only damaged three of the propellers and I brought spares. In the flight log on the DJI 4 app there is a moment where I held the right stick down and left 100% which must be related to its sudden acceleration but I havent pieced together exactly why I made that motion and don't want to spend too much time speculating without correlating it to the actual hight above ground. It's likely I began to start the CSC (controlled stick command) emergency shut off but Mavic lifted off unexpectedly and I stopped, but the whole thing happened so fast I don't remember my exact thought. Retrospectively, I am not surprised at the Mavic's skittish behaviour as I have read about numerous incidents with people crashing indoors in ATTI mode. I am, however, surprised that the full downwards throttle did not cut the power the way it does when I hand catch or land under normal circumstances. Looking at the flight log in the DJI app I can see the Mavic's altitude readings started at 0ft and decreases to -3 ft and then again to -6 ft. I have not yet dug into the data to see what the sonar sensors hight above surface reading was.
My thoughts are these:
--> Don't fly without good GPS signal.
--> Don't fly ATTI in lower light conditions or without substantial practice (a whole other discussion).
--> Incorrect GPS and/or downward visual sensor readings caused it to think it was not on the ground despite the sonar sensors so the fully closed throttle did not stop the rotors.
--> These incorrect signals, or a sudden response to the sonar readings contributed to its sudden upwards movement, lifting off again.
--> I should have jumped to the combined control stick emergency shut off (holding both control sticks in and down) the moment it didn't land according to my expectations but was on the ground (did I start this and not follow through?).
I looked briefly at the flight log on the app but have not delved into the data and don't think I can get the txt log file on my phone.
The link to the video is below, any insights on rotor shut off commands would be greatly appreciated.
Some specific questions I have:
--> How does the landing sequence work when the throttle is held 100% closed? Obviously at altitude holding the throttle all the way down doesn't shut the rotors. During my incident the Mavic was physically touching the ground, the two sonar sensors should have told it this. If I decided to land on the roof of a building, the drone would think it was above take off altitude but still be able to land.
--> I'm curious why holding the throttle all the way down shuts the rotors off when hand catching if the Mavic knows it is not close to the ground (I have hand caught the Mavic from the front grabbing just behind the gimbal without putting my hand under the sensors and it doesn't pull away from me).
--> Does the combined stick command work faster than the throttle down command to stop the rotors? How long does it take? I've tested this with the rotors turning while the Mavic is sitting on the ground, but I don't know if it takes any longer while flying and I'm not willing to test it while hovering and let it drop out of the air.
Looking forward to your responses!
Cheers,
Alexander
Sent from my iPhone using MavicPilots
New pilot here looking for some clarification. I learned a valuable lesson today - not to fly the Mavic unless it has excellent GPS signal. I've flown some various RC devices and toy drones and am a fixed wing Private Pilot, but I'm not prepared to fly without assistance from the cpu's. Before someone tells me off for not knowing how to fly in ATTI, the forums are clear you cannot turn off GPS and I have no way to practice. I am in Greece on holiday and late last night came across a beautiful 1000 year old church in the middle of a city square. Flying in an open space where there were no cars or people I was hoping to get a nice vertical pan (straight up then straight back down to land) showing it situated in the heart of a congested city block but the Mavic was picking up only a few satellites (fluctuating between 3 and 7). I tentatively lifted off to test its stability in a hover just above the ground. It was drifting and behaved like it was on ice, responding to my control inputs but continuing as if with substantial momentum in any direction. I've experienced this with other RC drones but not with the Mavic. It took me about fifteen seconds to be convinced it was not going to stabilize and that I was not going to take any risks (to the drone or to any property around me). Unfortunately, the decision to land is where the difficulty began. I held the left stick down 100% (stick mode 2) and the Mavic descended until it made contact with the ground. The rotors continued turning and the Mavic skittered sideways turning slightly then without any change in throttle position (I was still holding the throttle 100% down) it lifted off and accelerated sideways and backwards colliding with a low wall. I was lucky, the crash only damaged three of the propellers and I brought spares. In the flight log on the DJI 4 app there is a moment where I held the right stick down and left 100% which must be related to its sudden acceleration but I havent pieced together exactly why I made that motion and don't want to spend too much time speculating without correlating it to the actual hight above ground. It's likely I began to start the CSC (controlled stick command) emergency shut off but Mavic lifted off unexpectedly and I stopped, but the whole thing happened so fast I don't remember my exact thought. Retrospectively, I am not surprised at the Mavic's skittish behaviour as I have read about numerous incidents with people crashing indoors in ATTI mode. I am, however, surprised that the full downwards throttle did not cut the power the way it does when I hand catch or land under normal circumstances. Looking at the flight log in the DJI app I can see the Mavic's altitude readings started at 0ft and decreases to -3 ft and then again to -6 ft. I have not yet dug into the data to see what the sonar sensors hight above surface reading was.
My thoughts are these:
--> Don't fly without good GPS signal.
--> Don't fly ATTI in lower light conditions or without substantial practice (a whole other discussion).
--> Incorrect GPS and/or downward visual sensor readings caused it to think it was not on the ground despite the sonar sensors so the fully closed throttle did not stop the rotors.
--> These incorrect signals, or a sudden response to the sonar readings contributed to its sudden upwards movement, lifting off again.
--> I should have jumped to the combined control stick emergency shut off (holding both control sticks in and down) the moment it didn't land according to my expectations but was on the ground (did I start this and not follow through?).
I looked briefly at the flight log on the app but have not delved into the data and don't think I can get the txt log file on my phone.
The link to the video is below, any insights on rotor shut off commands would be greatly appreciated.
Some specific questions I have:
--> How does the landing sequence work when the throttle is held 100% closed? Obviously at altitude holding the throttle all the way down doesn't shut the rotors. During my incident the Mavic was physically touching the ground, the two sonar sensors should have told it this. If I decided to land on the roof of a building, the drone would think it was above take off altitude but still be able to land.
--> I'm curious why holding the throttle all the way down shuts the rotors off when hand catching if the Mavic knows it is not close to the ground (I have hand caught the Mavic from the front grabbing just behind the gimbal without putting my hand under the sensors and it doesn't pull away from me).
--> Does the combined stick command work faster than the throttle down command to stop the rotors? How long does it take? I've tested this with the rotors turning while the Mavic is sitting on the ground, but I don't know if it takes any longer while flying and I'm not willing to test it while hovering and let it drop out of the air.
Looking forward to your responses!
Cheers,
Alexander
Sent from my iPhone using MavicPilots
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