Mavic Crash - Battery issues, refuses to land.

[DroneForceOne]

It’s ok. That’s why we are all here, to support each other. VPS means Visual Positioning System. It’s that little camera type object / sensor in between your landing extenders on the bottom. That system helps keep the drone stable hover / landing / etc. I found a video for that calibration I was talking about here is the link:

Thank you VERY much, ill see it!

 

[DroneForceOne]

VPS = the downwards looking caneras and ultrasonic sensors that sense height above ground and horizontal movement at low altitudes. They were visibly disturbed and always thinking you were already on the ground preventing futher descent becaue you likely had the "landing protection" setting on. Most likely due to that landing gear that several have previously warned not to use, if you put one (unnecesary in most cases) you want one that extends out the back and leaves all the sensors perfectly clear.

The swollen battery is due to the severe overdistcharge that resulted, and it's good for the trash.

Never heard about this, Do not use...

Ill avoid using it, for sure...

Maybe the sunset shadow on the landing gear extensor blocked the VPS?

 

[sar104]

That's a strange one. It went into "Forced Landing" with 20% battery at 286 seconds but then really struggled to descend, as you mentioned, even though you also had full down throttle applied, which it ignored. It managed a few periods of nearly 3 m/s descent, interspersed with periods of barely descending. That continued until around 419 s when the battery voltage dropped too low and it entered uncontrolled descent from around 35 ft up, impacting at around 422.5 s.

VPS and barometric altitude were both functioning normally. VPS altitude was not reporting (as expected) until 421.5 s and 21.3 ft above the ground.

I cannot see any obvious cause in the flight log for that behavior.

 

[DroneForceOne]

That's a strange one. It went into "Forced Landing" with 20% battery at 286 seconds but then really struggled to descend, as you mentioned, even though you also had full down throttle applied, which it ignored. It managed a few periods of nearly 3 m/s descent, interspersed with periods of barely descending. That continued until around 419 s when the battery voltage dropped too low and it entered uncontrolled descent from around 35 ft up, impacting at around 422.5 s.

VPS and barometric altitude were both functioning normally. VPS altitude was not reporting (as expected) until 421.5 s and 21.3 ft above the ground.

I cannot see any obvious cause in the flight log for that behavior.

View attachment 22130

Thats correct, after a few moments commanding it in a descent, i realized it was not responding by checking the vertical speed. The moments with 3m/s descending was me, struggling it in a spiral descent.

What i am more confused is about the battery behavior, drained too fast, and was not accurate.

The VPS issue is not related with the non responsive descent?

 

[sar104]

Thats correct, after a few moments commanding it in a descent, i realized it was not responding by checking the vertical speed. The moments with 3m/s descending was me, struggling it in a spiral descent.

What i am more confused is about the battery behavior, drained too fast, and was not accurate.

The VPS issue is not related with the non responsive descent?

I'm not seeing anything unusual with the battery - it appears that you took off with only around 40% charge. It dropped as expected from there.



In terms of VPS I don't see any problems - for most of the flight you were far too high for it to register. It worked fine on take off up to around 50 ft, and then started reporting on the final descent at around 20 ft. There was a brief period early in the flight when it produced some spurious readings, but not towards the end.

 

[msinger]

@DroneForceOne, during many points in your flight, the downward sensors (VPS) were detecting the ground was near (even though it wasn't). That's normally caused by one of the following:

• Something is dangling beneath the Mavic (e.g. a GPS tracker antenna)
• A 3rd party accessory is installed beneath the Mavic (e.g. your extended landing gear)
  
• The downward sensors needs to be calibrated like this
• The downward sensors are dirty and need to be cleaned
• The downward sensors are damaged and need to be replaced (not a common problem)

When not in an auto landing mode (e.g. Forced Landing mode) and the throttle is not in the downward position, that would normally cause the Mavic to slowly ascend until it stops detecting the ground is near. The combination of the Mavic trying to auto ascend and Forced Landing mode trying to auto descend (or you manually holding the throttle in the down position) caused your Mavic to descend at a slower rate than usual.

The combination of the downward sensors detecting the ground and the throttle stick being in the full down position auto triggered Forced Landing mode at the following points in your flight:

• 2m 7.5s
• 2m 37s
• 3m 2.6s
• 4m 45.9s

If you ever see that happening mid-flight in the future, you should disable the Landing Protection setting. That will prevent the auto ascent/descent when the downward sensors incorrectly detect the ground is near. You'll find that setting in the following section of DJI GO:

 

[DroneForceOne]

@DroneForceOne, during many points in your flight, the downward sensors (VPS) were detecting the ground was near (even though it wasn't). That's normally caused by one of the following:

• Something is dangling beneath the Mavic (e.g. a GPS tracker antenna)
• A 3rd party accessory is installed beneath the Mavic (e.g. your extended landing gear)
  
• The downward sensors needs to be calibrated like this
• The downward sensors are dirty and need to be cleaned
• The downward sensors are damaged and need to be replaced (not a common problem)

When not in an auto landing mode (e.g. Forced Landing mode) and the throttle is not in the downward position, that would normally cause the Mavic to slowly ascend until it stops detecting the ground is near. The combination of the Mavic trying to auto ascend and Forced Landing mode trying to auto descend (or you manually holding the throttle in the down position) caused your Mavic to descend at a slower rate than usual.

The combination of the downward sensors detecting the ground and the throttle stick being in the full down position auto triggered Forced Landing mode at the following points in your flight:

• 2m 7.5s
• 2m 37s
• 3m 2.6s
• 4m 45.9s

If you ever see that happening mid-flight in the future, you should disable the Landing Protection setting. That will prevent the auto ascent/descent when the downward sensors incorrectly detect the ground is near. You'll find that setting in the following section of DJI GO:

View attachment 22134

Absolutely awesome @msinger. Well explained. Thanks for everything. So, in mid flight i should have gone in the menu and disabled it? ill keep this in mind...

Any thoughts about the battery swollen?

Do you know where can i buy this broken foot? I only found the entire arm with the engine.

 

[DroneForceOne]

I'm not seeing anything unusual with the battery - it appears that you took off with only around 40% charge. It dropped as expected from there.

View attachment 22133

In terms of VPS I don't see any problems - for most of the flight you were far too high for it to register. It worked fine on take off up to around 50 ft, and then started reporting on the final descent at around 20 ft. There was a brief period early in the flight when it produced some spurious readings, but not towards the end.

Thanks bro, u rock

 

[msinger]

So, in mid flight i should have gone in the menu and disabled it? ill keep this in mind...

In this case -- yes. Now that your Mavic is back on the ground, you can take some time to figure out what's causing it to auto ascend/descend. If you find the landing gear is the problem, then you'll need to disable the Landing Protection setting before taking off whenever using the landing gear (or find landing gear that does not cause that issue). I have a list of some other landing gear styles that might work for you here.

Any thoughts about the battery swollen?

Batteries can become swollen from doing things like:

• Using a poor quality battery charger (a non DJI battery charger)
• Storing the battery in a hot location (e.g. a hot car)
• Flying in very hot locations
• Keeping the battery fully charged for long periods of time

It's best to dispose of damaged batteries. They could potentially catch fire during charging and/or normal use.

Do you know where can i buy this broken foot?

If you're sure the arm is not damaged, you could ask @Thunderdrones if he'll sell you just part of an arm. If not, you can buy a new left front arm here on Amazon or here on eBay.

 

[sar104]

@DroneForceOne, during many points in your flight, the downward sensors (VPS) were detecting the ground was near (even though it wasn't). That's normally caused by one of the following:

• Something is dangling beneath the Mavic (e.g. a GPS tracker antenna)
• A 3rd party accessory is installed beneath the Mavic (e.g. your extended landing gear)
  
• The downward sensors needs to be calibrated like this
• The downward sensors are dirty and need to be cleaned
• The downward sensors are damaged and need to be replaced (not a common problem)

When not in an auto landing mode (e.g. Forced Landing mode) and the throttle is not in the downward position, that would normally cause the Mavic to slowly ascend until it stops detecting the ground is near. The combination of the Mavic trying to auto ascend and Forced Landing mode trying to auto descend (or you manually holding the throttle in the down position) caused your Mavic to descend at a slower rate than usual.

The combination of the downward sensors detecting the ground and the throttle stick being in the full down position auto triggered Forced Landing mode at the following points in your flight:

• 2m 7.5s
• 2m 37s
• 3m 2.6s
• 4m 45.9s

If you ever see that happening mid-flight in the future, you should disable the Landing Protection setting. That will prevent the auto ascent/descent when the downward sensors incorrectly detect the ground is near. You'll find that setting in the following section of DJI GO:

View attachment 22134

That's an interesting explanation and I think you are clearly correct. The earlier non-zero VPS readings do not seem to correlate in any obvious way with the onset of forced landing mode, but the final one, at 286 seconds, certainly does. I didn't pay enough attention to those VPS numbers. Furthermore, the intervals of normal descent rate during that final forced landing period occurred at exactly the same times that the VPS was not incorrectly detecting the ground.

 

[Cslucas34]

Well you have heard from several of us who came to the same conclusion reviewing your data and I hope we were able to get you the information you needed. Hopefully the calibration clues you into wether the landing gear extenders were the issue as we suspect.

 

[msinger]

The earlier non-zero VPS readings do not seem to correlate in any obvious way with the onset of forced landing mode

Forced Landing mode is initiated when the throttle is in the full down position while the downward sensors are detecting the ground is near.

 

[sar104]

Forced Landing mode is initiated when the throttle is in the full down position while the downward sensors are detecting the ground is near.

The graph below shows four instances of forced landing mode during that flight. You are completely correct - full down throttle plus small (non-zero) VPS value triggers it. Are these responses published somewhere or did you simply figure it out?

 

[msinger]

Are these responses published somewhere or did you simply figure it out?

I've learned the Landing Protection feature works this way through my own research and testing.

 

[DroneForceOne]

Well you have heard from several of us who came to the same conclusion reviewing your data and I hope we were able to get you the information you needed. Hopefully the calibration clues you into wether the landing gear extenders were the issue as we suspect.

You rock, thanks a lot!

Its great to have such help

 

[DroneForceOne]

I've learned the Landing Protection feature works this way through my own research and testing.

So, the Forced Landing mode is a protection for the Mavic, avoid it from hitting the ground when flying?

Great findings here. Im sure i am a better pilot now.

Thanks to all of you.

 

[DroneForceOne]

If you're sure the arm is not damaged, you could ask @Thunderdrones if he'll sell you just part of an arm. If not, you can buy a new left front arm here on Amazon or here on eBay.

I flew after the crash, tried a few maneuvers at low alt, it seems ok. Any suggestions of testing or inspectioning it?
Also, the bracket that limits the movement of the gimbal also broke:

I found the replacement of the entire plate.

 

[westonmavicpilot]

I would dispose of that battery immediately, or if keeping it to return to a local DJI retailer for warranty then at least keep it somewhere safe in a LiPo bag. It's amazing the amount of people who have got into the drone hobby who have no idea of the potential for harm LiPo's have - especially those folks who haven't been into the R/C hobby before and haven't experienced bulging soft pack LiPo's (which are much easier to damage). Some people dismiss being overly cautious when handling / charging / storing LiPo's and have the 'it'll never happen to me' attitude - and hopefully it wont! However, overcharge, over discharge and crashes can all cause damage to LiPo's that can lead to the worst happening. A perfectly normal looking LiPo can take out your house if the worst happens and is left unattended! A good rule of thumb is always store in a LiPo bag (not a cheap assed Chinese eBay LiPo bag, get something substantial, rated for more than you need), if possible never leave charging unattended or if thats not possible then charge in a location away from your property (garage?). Over the top, yes, but goes a long way to prevent the worst from happening.

There's loads of video's on youtube showing what happens when you intentionally over charge a LiPo, and lots showing what happens if you intentionally damage a LiPo.... but here's one that highlights why the advice above is best practice.

 

[Testman]

VPS = the downwards looking caneras and ultrasonic sensors that sense height above ground and horizontal movement at low altitudes. They were visibly disturbed and always thinking you were already on the ground preventing futher descent becaue you likely had the "landing protection" setting on. Most likely due to that landing gear that several have previously warned not to use, if you put one (unnecesary in most cases) you want one that extends out the back and leaves all the sensors perfectly clear.

The swollen battery is due to the severe overdistcharge that resulted from the aircraft waiting for an opportunity to land that never came, and is now good for the trash.

People really use too many poorly designed acessories on this poor Mavic.

Yes you are right.
A similar problem was happen to me, the cause was a twine block of my Trakimo that disturbed the sensor with "Landing protection" actived.
Bye

 

[msinger]

So, the Forced Landing mode is a protection for the Mavic, avoid it from hitting the ground when flying?

Forced Landing is a flight mode used by the Landing Protection feature. But, yes, it attempts to prevent an accidental impact with the ground.