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Mavic Mini Crash Water
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HedgeTrimmer
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JJB* Posted at 2-19 08:11
To make it more clear to all,

GPS count from 5 to 9 but reception only 2 on range 0 - 5,  level 2 is too low to get good hover accurancy.

Problem I keep seeing is: DJI needs to Kill Off - Auto-Take Off!  

Auto-Take Off is misleading, in a person would expect drone to wait till GPS Lock has been established.


At very least, Auto-Take Off should require a Pilot Over-ride anytime GPS Lock has not been established.
Over-ride could be Pop-Up warning, requiring Pilot to slide a button to confirm:  Yes, I really want to Fly without GPS...

2-19 23:55
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HedgeTrimmer
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Appears you were pretty close to fence when drone took off from your hand.
If drone was within 1-meter of fence, it is possible compass was effected.
If drone was within 15-centimeters of fence, it is very likely compass was effected.

If drone's compass was having problems on previous flights, possibly in need of calibration, then likely hood of compass being effected by metal fencing increases.  A compounding of errors.
2-20 00:08
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JJB*
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Guorium Posted at 2-19 19:34
Good GPS reception at 9 sat can be steady enough. Not a problem here.

You did not calibrate the compass and you stood too close to the metal fence. I moved the slider on phantomhelp to track the flight, and it really did not match up with the stick input (some roll must be used but none shown) in FRAP. I think the compass was not working for the whole flight. If you show us a screen record of the flight in DJI app, go to your flight record and tap on the flight and hit play, I believe we will see the compass was disabled as shown by the indicator at the bottom of your screen.

Hi Guoriom,

But what if...

I have search my database of error flights and found few similar cases.

To explain some basics (ofcourse you know this) ; for a steering-correcting loop you need values, actual value and a reference value.

With a IMU calibration you set 2 references for the pitch and roll. (calibration done on a level plane surface).  Yaw reference signal is not set. (we all put randomly are craft on a surface)

So when is the reference signal set for Yaw and GPS?
AFAIK at powering up and initialisation of the IMU.
Yaw reference signal is derived from the compass signal and altered by gyro data ; i.e. with manual input the compass 10 degrees left both yaw signals are changed, so no delta yaw and no corection needed by sw. If yaw is disturbed by wind etc the compass yaw signal is changed, delta this value and ref value ; thus correction.
MM shows more deviation between those 2 signals, but as long as there is no delta, no steering is done by sw. That is why not always direct after takeoff a faulty compass signal dictates a fly away. The moment yaw is disturbed (above treshold) thing can go wrong depending of the amount of deviation.
With a compass interference at the ground after takeoff compass yaw changes, as long as there is no need to steer to correct no probs. It gets a real problem if heading changes and sw start to correct this because craft is at other heading than the sw think it is ; fly away in progress.
This to be seen in data where those 2 values are diverting each other.

But what about GPS? in this flight the flight started in ATTI/OPTI mode, and was moved away from takeoff position.
GPS signal getting there, so when is the reference GPS position set ?  if set at one point and quickly after the LatLon position is changed, this due to low sat count and bad reception there is suddenly a delta between signals. in that case a drone wants to fly to the reference position! Now we have a GPS based fly away....
This is the same as hovering in steady GPS lock, push the craft away (by hand) and it will come back to its original position (ref pos).

As said, more flights wich started this way (ATTI>OPTI>RC fwd/roll input>GPS signals available with bad reception> a fly away.
See data for this flight, see the LatLon values.

AFAIK a GPS reception value of 2 is not enough for a stabilized hover. Number of sats is important as well where they are in the sky (9 close to each other is worse than 8 widely spread)



cheers
JJB

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2-20 01:55
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JJB*
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HedgeTrimmer Posted at 2-19 23:55
Problem I keep seeing is: DJI needs to Kill Off - Auto-Take Off!  

Auto-Take Off is misleading, in a person would expect drone to wait till GPS Lock has been established.

Guess its good to inform more newbies by an extra warning, why not.

But if all users check before take off their compass and wait for GPS lock; no problem at all.

If only....



cheers
JJB

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2-20 01:58
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m80116
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If I can I have my say you failed to comply with the basic rules of drone flying.

- Took off ignoring compass calibration and adjacent to railings.
- Took off without a GPS lock.
- Took off in these conditions almost above the water (so VPS sensors could not work reliably)

This is totally self inflicted. You haven't been lucky I admit... but you also did nothing to increase the AC to ground distance for a safe clearance before everything went awry.

The GPS was not locked until 20.5 seconds into the flight. You really sough it I am afraid.

If it was my Mavic Mini I would already be at work for the recovery plan.
2-20 03:57
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InspektorGadjet
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Man, I´m sure in the future, all drones will have things built in like OA sensors, and god  knows what sort of tech... one thing I see clearly is that Drones must have some sort of "floating" capability either by air chambers withing the drone, or some airbag thingy that deploys after soaked or in contact with water.

Not just to save the craft, and money of the user, but to stop batteries from contaminating lakes, ponds, the sea...
Nature and pilots will benefit from this...
2-20 11:31
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Eragorn87
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InspektorGadjet Posted at 2-20 11:31
Man, I´m sure in the future, all drones will have things built in like OA sensors, and god  knows what sort of tech... one thing I see clearly is that Drones must have some sort of "floating" capability either by air chambers withing the drone, or some airbag thingy that deploys after soaked or in contact with water.

Not just to save the craft, and money of the user, but to stop batteries from contaminating lakes, ponds, the sea...

Holy words! But they will end up weighing more. Anyway I found the drone inside the lake after a morning of research and I brought it to the assistance.I paid for the replacement but I am very happy. Thanks to everyone for the support and let's hear what the support will answer me after checking the logs
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2-20 12:52
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hallmark007
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Eragorn87 Posted at 2-20 12:52
Holy words! But they will end up weighing more. Anyway I found the drone inside the lake after a morning of research and I brought it to the assistance.I paid for the replacement but I am very happy. Thanks to everyone for the support and let's hear what the support will answer me after checking the logs

Great job best of luck .
2-20 12:58
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HedgeTrimmer
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Eragorn87 Posted at 2-20 12:52
Holy words! But they will end up weighing more. Anyway I found the drone inside the lake after a morning of research and I brought it to the assistance.I paid for the replacement but I am very happy. Thanks to everyone for the support and let's hear what the support will answer me after checking the logs

Glad to see  you found your baby Mavic.  
2-20 14:03
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m80116
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For me that drone is 100% functional with a new battery.

I know this by experience... certainly that wasn't clear stream water, but murky water doesn't necessarily mean it would damage the electronics.

Should you need to rehabilitate it I suggest you take off every shield in the FC board, displace the water with isopropyl alcohol spray and subsequently wash it with de-oxid and a soft brush.
Glad to see your drone being recovered.
2-20 15:44
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InspektorGadjet
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Eragorn87 Posted at 2-20 12:52
Holy words! But they will end up weighing more. Anyway I found the drone inside the lake after a morning of research and I brought it to the assistance.I paid for the replacement but I am very happy. Thanks to everyone for the support and let's hear what the support will answer me after checking the logs

Oh man that is awesome! so glad you got it!
2-21 00:26
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Eragorn87
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m80116 Posted at 2-20 15:44
For me that drone is 100% functional with a new battery.

I know this by experience... certainly that wasn't clear stream water, but murky water doesn't necessarily mean it would damage the electronics.

I preferred to use the DJI Care Refresh guarantee and pay for the replacement of the vehicle, unfortunately the battery is not a guarantee! Patience!

Even DJI Support replied:
The unfortunate incident that occurred to your aircraft has been confirmed as a warranty case according to our data analysis.

If the aircraft cannot be recovered, we would like to offer you a replacement, Mavic Mini (without the remote controller and battery charger).
2-21 00:35
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m80116
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Yep...the good about DJI Care Refresh is that for a small fee they provide a spare drone regardless of what happened, as long as you bring back the old one.

As for the old battery I suggest you do not throw it away: there's an INCREDIBLE WORLDWIDE SHORTAGE and original batteries can go as high as 120 EUR or more (from 3rd party sellers), if still available at all. Beyond that the cells are still good... the Interweb just needs to find a way to bring back to life the little bms chip.

2-21 02:31
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hallmark007
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Eragorn87 Posted at 2-21 00:35
I preferred to use the DJI Care Refresh guarantee and pay for the replacement of the vehicle, unfortunately the battery is not a guarantee! Patience!

Even DJI Support replied:

Great news , I had a good feeling that this case was very similar to others I’ve seen and that warranty would be offered, I’m sure dji gave little details as they usually, but the case was so close to others that working out what happened wasn’t difficult .

Enjoy your new craft and be a little more cautious a good exercise for pre flying I’ll leave below.


1/ Never calibrate Compass unless prompted to.

2/ start AC leave until you receive enough gps lock ,

3/ if you get Compass interference turn off AC and move to another location,
without interference.

4/ In bottom left hand corner on your map you will see small red triangle, check to make sure that this triangle is pointing in the same direction (heading) as your AC, this will show good compass on the ground.

Raise AC to height of 8ft
Hover for 20 seconds
Fly forward 2ft
Backward 2ft
Left 2ft
Right 2ft
Up 2ft
Down 2ft
Yaw left
Yaw right
Each time returning to hover position
If you have a good horizontal each time, you will then know you have good GPS good IMU and good Compass, and your ready to fly.

This exercise takes less than 2 minutes and is worthwhile doing before every flight,
2-21 02:54
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Eragorn87
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hallmark007 Posted at 2-21 02:54
Great news , I had a good feeling that this case was very similar to others I’ve seen and that warranty would be offered, I’m sure dji gave little details as they usually, but the case was so close to others that working out what happened wasn’t difficult .

Enjoy your new craft and be a little more cautious a good exercise for pre flying I’ll leave below.

The support did not give me an explanation on the logs, I hope they will let me know anyway. I will do as you suggested to me on each flight.
Thank you
2-21 03:08
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virtual
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Eragorn87 Posted at 2-21 03:08
The support did not give me an explanation on the logs, I hope they will let me know anyway. I will do as you suggested to me on each flight.
Thank you

What a rescue mission! Enoy your new Mini and be patient with preflight check like hallmark007 suggested.
2-21 03:57
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JJB*
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Eragorn87 Posted at 2-20 12:52
Holy words! But they will end up weighing more. Anyway I found the drone inside the lake after a morning of research and I brought it to the assistance.I paid for the replacement but I am very happy. Thanks to everyone for the support and let's hear what the support will answer me after checking the logs

Good luck and many happy dry landings with your replacement MM !!

cheers
JJB
2-21 04:04
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Eragorn87
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Support's reply email: (Do you think they will repair or replace it? I hope they will replace it)

Dear Customer,

Thanks for getting back to us.

According to the data analysis, the flight accident was due to a possible compass interference, which caused that the aircraft drifted and crashed finally. There was no pilot's error and we determine to cover it under warranty. For safety concerns, it is suggested for the pilot to avoid flying near any tall buildings, steel structures, mountains, rocks or even trees which may affect the accuracy of the on-board compass and block the GPS signal. Also, calibrating the compass over or near any of these objects or material can cause issues in flight.

We are glad to hear that the aircraft is retrieved. We are unable to offer you the replacement service directly since it is only applied for the flyaway cases. We will offer you free warranty service instead. It's advised for you to send back the aircraft for diagnostic, then the related department will offer solutions based on the damage assessment result to see whether to have it repaired or get it replaced. And we will keep you updated.

In regards to the inquiry about to send back the aircraft, we will transfer it to the designated department that deals with issues as such for further assistance.

They will for sure handle your concerns accordingly at the earliest.

Thanks for your patience and understanding. Have a nice day.


Best Regards,

Dora
2-25 01:10
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InspektorGadjet
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Glad support has decided to help you!
What I find a bit extreme is the suggested limitations "For safety concerns, it is suggested for the pilot to avoid flying near any tall buildings, steel structures, mountains, rocks or even trees which may affect the accuracy of the on-board compass and block the GPS signal."... basically only open fields then?

Also even though they have agreed is covered by warranty they say "We are unable to offer you the replacement service directly since it is only applied for the flyaway cases."
A bit confusing and contradictory, I really hope the process doesnt take too log and you will be flying soon!

2-25 01:31
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hallmark007
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Eragorn87 Posted at 2-25 01:10
Support's reply email: (Do you think they will repair or replace it? I hope they will replace it)

Dear Customer,

Great to get the explanation , it should also help others understand, thanks for posting .
2-25 09:42
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Guorium
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JJB* Posted at 2-20 01:55
Hi Guoriom,

But what if...

I find the response a bit hard to interpret. Let me make sense of it.

I suppose you say when GPS registers a bad location (not true) when reception is not good, then it registers a good signal. The difference in coordinate makes MM want to fly to the wrong location thus fly away? I suppose that could happen. I did an opti takeoff with poor GPS reception and 5 sat over water. VPS kept it steady til I gathered a solid reception higher up, the flight was very safe.

No sure about how delta in yaw can cause fly away. I find the idea of wind causing change in yaw dubious. If the mini has the wrong yaw ref set due to interference, it should still have a direction to refer to. At most I think it would give use an compass error on the screen and unreliable RTH, not a flyaway.
2-25 16:50
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JJB*
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Guorium Posted at 2-25 16:50
I find the response a bit hard to interpret. Let me make sense of it.

I suppose you say when GPS registers a bad location (not true) when reception is not good, then it registers a good signal. The difference in coordinate makes MM want to fly to the wrong location thus fly away? I suppose that could happen. I did an opti takeoff with poor GPS reception and 5 sat over water. VPS kept it steady til I gathered a solid reception higher up, the flight was very safe.

Hi Guorium,

On this forum it is promoted to do before take off checks, especially check the compass heading at the ground. Why? to prevent a fly away due to compass/yaw error.

Situation1 : all OKE ;

Craft on the ground is actual facing N and compass is showing N,Into hover and than no stick input,

Wind breeze wich moves craft backwards,
SW calculates (using GPS + compass data) needed input to steer to the old postion > forward input = all OKE

Situation2 : N-OKE ;
Craft on the ground is actual facing N and compass is showing W, (but not checked by pilot)Into hover and than no stick input,
Wind breeze wich moves craft backwards,
SW calculates needed input to steer to the old postion > right input = craft moves to the right (back already) of the old position, thus further away  and more correction needed etc ect

A great example of this type of flyaway to see at >  https://forum.phantomhelp.com/t/mavic-mini-flew-away-on-me/4477
Craft heading on the ground South and takeoff South (told by the pilot and can be checked by the video, drone compass 055), see the result.

Compass indicated heading is not changed after take-off, during takeoff and gaining height, as long as the position is not really changed no correction is needed, same when flying forward, no problem yet. Once there is a change in position with some heading changes too (not done by RC input as yaw signals are both changing) the fly-away starts.

On few flights on this forum this was the problem, checking logs is hard as in the log it is not seen at wich heading the craft actual was heading at takeoff.
Only asking the pilot to inform the forum this heading makes the analysis to be done correct.

What we do not see in logs is that the compass heading is changed after takeoff at few meters above the ground, so compass interference/wrong heading is not see by a moving compass back to the real actual heading after takeoff. (well i have not seen any of this in my large database of error flights). Apparantly in this situation the app does not give a warning.

In some flights suddenly during flight (after 1 minute, or 2 or 14 minutes) compass heading is changed, not few degrees but large changing values.
I have no clue how that is possible. A hardware fail, power peak to this part of the system??. During flight at height hardly possible to 'eat' an interference to the compass/yaw system. But the effect on the drone is the same, SW steering into to wrong direction, a fly away.
Some cases seen on this forum when the flight was screen recorded, you will see a rapid change on the compass indicator where the drone does not yaw ofcourse.
Cannot explain really but sometimes entering  a RTH mode does bring yaw signals back to each other.

So is it important to check your compass indication in the app before takeoff? Ofcourse a 100% YES, as this is a simple way to prevent a fly-away right after take-off!!
For other fly-aways wich occur during a normal started flight, wish i had the knowledge to pin point the cause of this!

For the GPS part, when starting a flight in OPTI due to low sat  and/or reception ; guess it depends how the GPS signals (quality) getting in the system and how fast from 0 to normal number and reception. So not all in OPTI started flight goes wrong, but is it a coincidence that few fly-aways started their fligt in OPTI? guess yes...a coincidence but not sure about that.
cheers
JJB










2-26 01:48
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