Too fast descent whilst using return to home

[Finitiative]

My 1st day flying with the Mavic Pro and crashed badly whilst descending to land (using the return to home function).

Would like to learn what I did wrong so that I don't make the same mistake again, i hope the repairs aren't too costly.

Log file:

DJI Flight Log Viewer | Phantom Help

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Problem? Pressed return to home and watched it return. Above the home point it descended much much faster than it is supposed to and crashed straight onto paving.

Was unit in a crash? Yes.

What have you tried so far? I checked if drone can still fly, seems okay it can fly but gimbal broken (can't move up/down). Submitted request for repair.

What device are you using ( iphone , ipad, Samsung , etc)? iphone for video feed and remote control for flying.

What firmware are you running ( aircraft, remote controller)? Not sure.

What Go app version are you using? Dji Go 4

Any modification? (if so what) propeller guards and carbon fibre gimbal guard plate is fitted.

Did you change anything or install any apps? (if so what) None.

Do you have a video or pictures of the problem? (if so post link)
Log file: DJI Flight Log Viewer - PhantomHelp.com

 

[RadioFlyerMan]

Don't know if this is the reason, but did you have the Downward Vision Positioning system on?

 

[Finitiative]

The setting, "Enable Vision Positioning" is enabled and "Landing Protection" is also enabled.

 

[sar104]

Why did you keep full down throttle while it was autolanding? It appears to me that you flew it into the ground:

 

[Meta4]

My 1st day flying with the Mavic Pro and crashed badly whilst descending to land (using the return to home function).

Would like to learn what I did wrong so that I don't make the same mistake again, i hope the repairs aren't too costly.

The setting, "Enable Vision Positioning" is enabled and "Landing Protection" is also enabled.

The settings show VPS was on and Obstacle avoidance was off.
But there is no VPS data at any point in the flight so I'm not sure what was going on there.
Was the flight in well lit conditions?

The auto-descent started normally at 5:38.3 but at 5:48.2 there's some crazy joystick input with full stick input going full up and full down on both sticks till 5:57.
That's what sent the descent off.

 

[Finitiative]

Why did you keep full down throttle while it was autolanding? It appears to me that you flew it into the ground:

It looks like I did. Very disappointing.

 

[Finitiative]

I tested today, even with full throttle downwards it descends and lands softly when it gets to about a meter from the ground, it doesn't crash land like what happened on the return to home automatic landing.

Whilst flying this afternoon I also noticed I got the same error as in these posts: Downward sensor error (Downward sensor failure, land as soon as possible.) This is the same error message I got in previous flights before the drone crash landed. I also noticed this error message doesn't show up in the log files, same as what is mentioned in the other post and next time I'll try to take a screenshot.

I sent the supplier a copy of the log files, awaiting their response on the analysis.

My Mavic Pro is a refurbished unit from DJI, is it possible to check why the previous owner sent it back to them?

 

[Finitiative]

I've checked the video footage of the crash (see below for link) and noticed the following:

- At 5m 45s into the flight the drone finished RTH turn in preparation of landing. In the video that is around 7seconds. 5 seconds later the drone crash landed on the paving, that is about 12 seconds on the video.
- At 5m 48.4s - 5m 49.3s I was pressing full throttle up to slow down the drone but there was no slowing down . The IMU altitude indicated 62.7ft. The drone continue descending at a very fast speed ignoring the throttle up command.
- At around 5m 49s - 5m 50s the drone crashed (about 5 seconds after turning as per the video)
- At 5m 49.7s I was full throttle down to stop the motors since the drone was on the ground, but to no avail it kept fluttering about on the ground for about 15 seconds (as per the video) until it finally stopped the motors I guess with the cross shift command on the controller and I then picked it up.

Video:

Conclusions:
- I did not press full throttle down whilst it was auto landing. there was no inputs when it started auto landing, when I noticed it was coming down to fast I was throttle up for about a second to prevent the crash but it didn't slow down.
- after the crash I used full throttle down to get it to stop the motors, but the motors didn't stop I had to do cross shift to get it to stop. I assume this is because the drone was still thinking it is about 50ft in the air.
- There was no VPS data.
- Malfunction of some kind during the auto land.

 

[sar104]

I've checked the video footage of the crash (see below for link) and noticed the following:

- At 5m 45s into the flight the drone finished RTH turn in preparation of landing. In the video that is around 7seconds. 5 seconds later the drone crash landed on the paving, that is about 12 seconds on the video.
- At 5m 48.4s - 5m 49.3s I was pressing full throttle up to slow down the drone but there was no slowing down . The IMU altitude indicated 62.7ft. The drone continue descending at a very fast speed ignoring the throttle up command.
- At around 5m 49s - 5m 50s the drone crashed (about 5 seconds after turning as per the video)
- At 5m 49.7s I was full throttle down to stop the motors since the drone was on the ground, but to no avail it kept fluttering about on the ground for about 15 seconds (as per the video) until it finally stopped the motors I guess with the cross shift command on the controller and I then picked it up.

Video:

Conclusions:
- I did not press full throttle down whilst it was auto landing. there was no inputs when it started auto landing, when I noticed it was coming down to fast I was throttle up for about a second to prevent the crash but it didn't slow down.
- after the crash I used full throttle down to get it to stop the motors, but the motors didn't stop I had to do cross shift to get it to stop. I assume this is because the drone was still thinking it is about 50ft in the air.
- There was no VPS data.
- Malfunction of some kind during the auto land.

According to the log file - as shown in the graph above - you applied full down throttle when the aircraft was descending through 20 m. The lack of VPS data is strange, and since it uses VPS to detect the ground and slow down before landing, that could be a contributory factor.

 

[Finitiative]

According to the log file - as shown in the graph above - you applied full down throttle when the aircraft was descending through 20 m. The lack of VPS data is strange, and since it uses VPS to detect the ground and slow down before landing, that could be a contributory factor.

Indeed the VPS data is odd and today I got a downward sensor failure, same error i got during first flights after unboxing.

Where it says 20m (measured by IMU) it was already on the ground and not a correct reading, this is evident from the video footage which indicates after turning in preparation for landing, at about 5m 40s it started descending (96.5ft) and 5 seconds later at 5m45s the drone was still at 94.5ft and at 5m46.4 at 90ft. This does not match the video which indicates it took about 5 seconds until crashing on the paving. The graph indicates the descent was about 10 seconds which is 5 seconds longer than what the video shows.

Since it was already on the ground I applied full down throttle at 5m 48.4s to get it to stop the motors but it didn't since it was still thinking it is in the air. The IMU is definitely not indicating the correct height and without VPS like you mentioned it is not able to detect the ground and slow down. In addition, the GPS readings were way off, it crashed about 4 - 5 meters from where the GPS indicated it crashed.

I'm looking forward to a response from the supplier, hopefully the repairs is not too expensive and/or repaired on warranty if the sensors are indeed having issues.

 

[old man mavic]

i notice you say you have a carbon fibre gimbal guard fitted is this the type that fits to the bottom heat tray on the mav ,i only ask because there have been issues with the guard interfering with the down wards sensors

 

[Finitiative]

i notice you say you have a carbon fibre gimbal guard fitted is this the type that fits to the bottom heat tray on the mav ,i only ask because there have been issues with the guard interfering with the down wards sensors

Yes it is those that fit to the bottom - I will remove it and see if the downward sensor error stops appearing.

 

[old man mavic]

Yes it is those that fit to the bottom - I will remove it and see if the downward sensor error stops appearing.

View attachment 67537

they have caused the sensors to not operate correctly have seen videos about it on youtube

 

[Simmo]

they have caused the sensors to not operate correctly have seen videos about it on youtube

Absolutely! In my early Mavic days, I saw the gimbal as the weak point and wanted to protect it, so looked at these 'gizmo's' to help, I hadn't actually purchased one yet when the bad news stories started coming out... never bought one....