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So my Mavic just dropped from the sky... What the ...
2189 20 2017-1-13
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stratosHD
lvl.4
Flight distance : 1231280 ft
Australia
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Well, yes just as the title reads. I am very worried and confused at what just happened now.
As I type this im exporting the logs form my Mavic, it just dropped from the sky.  

I was taking a safe and even a bit boring flight around 7pm today. There was good visibility and decided to fly in a nearby Golf course.
I was just flying on around the area and decided to just land as normal. I took off from a 'Green' of one of the holes.
As I was returning to land everything looked normal, open area , flat non obstructed, I had about 80% batttery left.  I was about to land hovering about 1 metter from the ground, I pull the joystick down to land and it suddently dropped to the ground just like that.
It hit the grass violently, I reacted when I saw it falling and push the stick up to prevent the fall but it just regain altituted after it bounced from the ground.  I heared the props hitting the body of the mavic when it hit the ground, then I hover it for a couple of seconds in disbelief on what just happened!

Then again I tried landing, exactly on the same spot without issues. After the crash I inspected the props and both the rear ones got damaged.
The blades also left some scars on the back of the Mavic's body, just above the exhaust vents.

Im really really dissapointed on what just happend and trashed my confidence on my Mavic. Tomorrow I was supposed to get some shots and yes I do have some spare props but Im worried of this happening again.

Mindy and Ken, can you please help me look after this case please? and help me understand what happened??

Details:

Iphone 6,
DJI Go 4 app, latest update.
Firmware : 1.03.0200 (Mavic and Batteries)
Controller as well updated with latest firmware.

As soon as the logs and flight record are downloaded will upload.

Crash Pics:

https://files.mycloud.com/home.php?brand=webfiles&seuuid=bf30218402334f4abf809bdfa7b8ad74&name=Pics

Notice the one that shows the "two holes" that the front arms did on the green. :/

Healthy Drones upload:

http://healthydrones.com/main?flight=7ccbfd791d54e36dbdcae83a72bc9199&page_id=GENERALNotifications


2017-1-13
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Nomadic
lvl.4
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Flight control log is needed, you need to use the DJI ASSISTANT to export it.
2017-1-13
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stratosHD
lvl.4
Flight distance : 1231280 ft
Australia
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Nomadic Posted at 2017-1-13 04:11
Flight control log is needed, you need to use the DJI ASSISTANT to export it.

Thanks buddy I have extracted the full logs, ready to provide.
Care to take a look?
2017-1-13
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Wandering Cloud
lvl.4
Flight distance : 839633 ft
United Kingdom
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7PM good visibility at this time of the year in Switzerland?
2017-1-13
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Angelo26
Second Officer
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Austria
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Wandering Cloud Posted at 2017-1-13 05:13
7PM good visibility at this time of the year in Switzerland?

well commented
2017-1-13
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DJI-Ken
DJI team
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I got your PM, thank you.
I've forwarded it on.
Add your email to the PM so I can review the last flight.
2017-1-13
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SPARKFLASH
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Did you push both controller joysticks down and to the bottom?  If so thats an emergency ability to make the drone suddenly stop and fall.  That would make sense if thats what happened?
2017-1-13
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Mir
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Wandering Cloud Posted at 2017-1-13 05:13
7PM good visibility at this time of the year in Switzerland?

He's flying the mavic in Australia, not Switzerland
2017-1-13
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Wandering Cloud
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Mir Posted at 2017-1-13 09:29
He's flying the mavic in Australia, not Switzerland

In that case it is down to the monochrome surface of the green that cause VPS to stop functioning.  
I have similar issue when landing on a super white sandy beach under midday sun.  Sometime the Mavic will land really fast without stoping few feet above the ground first. Had I not react quickly, the drone will smash onto the ground while I try to land the craft.
2017-1-13
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Jason Lane
Second Officer
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Philippines
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Wandering Cloud Posted at 2017-1-13 10:01
In that case it is down to the monochrome surface of the green that cause VPS to stop functioning.  
I have similar issue when landing on a super white sandy beach under midday sun.  Sometime the Mavic will land really fast without stoping few feet above the ground first. Had I not react quickly, the drone will smash onto the ground while I try to land the craft.

I would have thought the Mavic relies more on the ultrasonic sensors for distance measurement, rather than the optical sensors.
2017-1-13
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stratosHD
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DJI-Ken Posted at 2017-1-13 07:57
I got your PM, thank you.
I've forwarded it on.
Add your email to the PM so I can review the last flight.

Thanks ken will do it ASAP
2017-1-13
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DJI-Ken
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stratosHD Posted at 2017-1-13 11:26
Thanks ken will do it ASAP

Sounds good, thanks.
2017-1-13
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Griffith
First Officer
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United States
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Jason Lane Posted at 2017-1-13 10:34
I would have thought the Mavic relies more on the ultrasonic sensors for distance measurement, rather than the optical sensors.

It should use ultrasonic sensors for landing, optical for finding the exact takeoff spot (fine tuning for gps).
If everything was functioning properly, a possible explanation might be a poorly ultrasound - reflective surface, which,  in the case of a Green is improbable.

One question might be how Mavic measures higher altitudes (GPS, barometric pressure ?).  Ultrasound has too short a range - guessing 20-30 ft.
2017-1-13
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MacIak
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Griffith Posted at 2017-1-13 13:30
It should use ultrasonic sensors for landing, optical for finding the exact takeoff spot (fine tuning for gps).
If everything was functioning properly, a possible explanation might be a poorly ultrasound - reflective surface, which,  in the case of a Green is improbable.

GPS and when atti barometric. Need more size for radio altimeter.
2017-1-13
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stratosHD
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I thought the mavic had some built in redundancy bot using optical and sonar to find the ground. Can It be that my sensors stopped working for a sec???
2017-1-13
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Griffith
First Officer
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MacIak Posted at 2017-1-13 13:36
GPS and when atti barometric. Need more size for radio altimeter.

If barometric pressure is involved in relative altitude determination, it can be off if the local barometric pressure changes.

Out of curiosity, did you notice your displayed relative altitude while you were hovering in preparation for landing?
2017-1-13
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Griffith
First Officer
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United States
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Having little knowledge of the actual internals of the Mavik systems, I'm relying on how I might have approached the problem as a design engineer.  

- GPS can be used to measure altitude (but in my experience is much less accurate than its lateral positioning accuracy.  
- Barometric pressure -based altimeters are common in most light aircraft - still not accurate enough to land autonomously, Plus, it's subject to weather conditions.  
- Radio altimetry  is accurate but too costly (and not sufficiently miniaturized).  
- Ultrasound is accurate but has a limited range.
- monoscopic optical CAN yield some altitude information in very  specific circumstances - like unique and distinctive surface patterns.  I think DJI uses the bottom optics to locate help locate the take-off position using a pattern recognition algorithm

I think If I were designing an autonomously landing drone today, I would utilize GPS or barometric altitude to get within a few feet of ground and then switch to US to get  down the last few feet.  Don't know if that's what DJI did here.  I certainly wouldn't leave US turned on for the entire flight.

Would be really interesting to get some DJI engineering comments on the Mavic landing system. Thanks for letting me brainfart.
2017-1-13
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Logger
Second Officer
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Australia
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Almost as if it sensed it was on the ground when you were in the hover and it shut the props down when you went Left Stick down. Odd.
Alternatively VPS may have been deactivated by accident or disabled by the system for some reason. Then you would need to stick down much more gently than normal to land.
DJI Ken should be able to see what was going during the landing in the logs. You can also check yourself to see how much downstick you gave it.
2017-1-13
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stratosHD
lvl.4
Flight distance : 1231280 ft
Australia
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Logger Posted at 2017-1-13 19:02
Almost as if it sensed it was on the ground when you were in the hover and it shut the props down when you went Left Stick down. Odd.
Alternatively VPS may have been deactivated by accident or disabled by the system for some reason. Then you would need to stick down much more gently than normal to land.
DJI Ken should be able to see what was going during the landing in the logs. You can also check yourself to see how much downstick you gave it.

Yes exactly. That when I commanded to land it felt that it completely shut down the engines as if it believed it was already on the ground.  I was lucky that the damage were only 2 props and some damage to the outside of the craft.

But if it would have hit front first my gimbal would have been hit really hard.
Ken do you have any updates?
2017-1-13
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stratosHD
lvl.4
Flight distance : 1231280 ft
Australia
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Wandering Cloud Posted at 2017-1-13 05:13
7PM good visibility at this time of the year in Switzerland?

Mate I am in australia, were are in Summer and its quite bright at 7pm.
2017-1-13
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stratosHD
lvl.4
Flight distance : 1231280 ft
Australia
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SPARKFLASH Posted at 2017-1-13 07:59
Did you push both controller joysticks down and to the bottom?  If so thats an emergency ability to make the drone suddenly stop and fall.  That would make sense if thats what happened?

No, only push them down ,  from hover down to land the craft.
2017-1-13
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