Hello everybody,

I was flying my MM yesterday when i suddently lost control as i was manually coming back to the home point.
Here's the flight log : https://www.phantomhelp.com/LogViewer/BB9Z85HL6N3P6U2CSKQ3/#

As you can see, everything seems to be ok until 9m50s, i went far (2176ft) from the home point the connection became bad then i decided to come back to home point. It works until i reach the distance of 1100feet from home point. the connection with RC became really really bad and i could not control the drone anymore. it almost touch the water at 13min10 and but it gain altitude again, i had a message about propellers rotating too fast, and at the end the auto RTH starts but the drone keeps flying away from home point (the connection was still bad and i still can't control the drone). and I never get back the connection even walking around the lake. drone lost ....


What do you think about that ? is there a dysfunction of the drone ? or was it my fault at some point ?


Thanks
Clément

Hi Clement,

Sorry for your loss.

But too many " Alerte vent fort. L'appareil ne peut retourner au point de dpart automatiquement. Rduisez l'altitude immdiatement et retournez au point de dpart manuellement(Code: 30149)" in the log.

At 4m39 the first loss of contact, into RTH mode and it did not flew back home, too much wind to win that battle. Distance first 818 meters, at cancelling RTH distance out 827 meters. (this in 20 seconds)
So you was warned about MM not able to fly back to home in RTH mode at that time and flying height.
At 5m20 MM in RTH mode, due to loss of contact. Distance out 836 meters. 4 secs later CX RTH at distance 850.
warning: ( 6Radiocommande dconnecte de l'appareil(Code: 30029)Alerte vent fort. L'appareil ne peut retourner au point de dpart automatiquement. Rduisez l'altitude immdiatement et retournez au point de dpart manuellement(Code: 30149). #Perte du signal de la radiocommande. 30029#Perte du signal de la radiocommande)

In the log now many "NotEnoughPower" messages, In Sport mode MM not able to pitch down enough to get speed so only doing 2.7 m/s to get to home.
At 6m58 again loss of contact, MM in RTH at 712 meters out. Full stick forward and speed to hope now 4 - 6 m/s.
RTH cx, into Sport at 5m22, fluing toward ahome.
At approx 7m wind increased (i guess) as the speed to home decreased. Now 318 meters away from home.

At 13m "Les hlices tournent trop rapidement. Retournez au point de dcollage et atterri. 30246Les hlices tournent trop rapidement. Rsistance au vent impact. Retournez au point de dcollage et atterrissez rapidement. Vrifiez si l'hlice sur l'ESC sonore est de ou endommag"

In the last RTH heading was oke but MM moved further away.....see chart.
PS first part of the flight mot in the log.

So too much wind to get the MM back home, in Sport mode manual flying it was possible but in a OutOfControl RTM mode (so you could not increase speed) it was not possible to fly back to you. AND because the MM did not pitch down enough to make speed because of the NotEnoughPower messages, in the FW .5 this was 'repaired'.

cheers
JJB

Thanks for your feedback!

I could post the log of the beginning of the flight if it can help but the app makes two different log files

What does "NotEnoughPower" messages mean ? i know there was some gusts especially when the MM was far away on the lake but then they did not last and then the drone could continue to fly or come home. i also think it is normal i lost the signal in the middle of the lake as i was far from home point.

Is there some explanation on why the signal get really weak at a point when the drone come back ? because if not, i could have made an emergency landing at another point around the lake and then collect the drone (and i have the refresh & care insurance...). And there was really less wind from 13m30s as this area is more protected from the wind (i do windsurfing and we could never to this part of the lake because of the lack of wind).
And with this lack of signal I couldn't locate the drone and where it could have potentially gone ... we were 3 and searched it for almost 2 hours ...
What do you also mean that in FW .5 it was corrected ? i did not had the last firmware ? I made a firmware update last week.

Thanks again !

cpetit Posted at 6-7 02:26
Thanks for your feedback!

I could post the log of the beginning of the flight if it can help but the app makes two different log files

Hi,

Sorry, my mistake. You have indeed the latest FW.  

The internal message NotEnoughPower is there when the craft is using all its power to fullfill your RC demands or when its flying in an auto mode and needs all the power.

The FlyApp did warn you, showing many times (> 40 or so) " Alerte vent fort...ect", and " Les hlices tournent trop rapidement..ect"
I was not there so i cannot discuss about yes / no too much wind for a MM. But in your first RTH it was clear that your MM did not had the power to return to home just in RTH mode.And yes....  if you did not loose contact than in Sport mode it could have made home....well, at the end the with < 35% batt level your MM slowed down.
So i am not sure if you had made it home.

No need for the first part of this flight, normally a flightrecords covers the whole flight. Did you had to restart your mobile device this flight ?

My guess where it mayby landed is the orange marker.

cheers
JJB

Concerning the fact i have 2 flight records, i do not have any explanations. but i am sure i did not restart my phone or the RC. I think i maybe just lost connection at this time.

Just to mention that I made the same flight a few minutes before, same weather conditions, and no problems at all... including no connection problem. And i believe that if i did not have this connection problem I could have saved the drone and made an emergency landing. You mean that if the craft is using all his power, it could explain that less power is used to communicate with the RC and reduce the range i could get the signal ?

Howeve , how did you get that orange marker ? is it something on the log ? do you have exact gps coordinates ? i can go and check if it is there
Thanks a lot.

cpetit Posted at 6-7 04:22
Concerning the fact i have 2 flight records, i do not have any explanations. but i am sure i did not restart my phone or the RC. I think i maybe just lost connection at this time.

Just to mention that I made the same flight a few minutes before, same weather conditions, and no problems at all... including no connection problem. And i believe that if i did not have this connection problem I could have saved the drone and made an emergency landing. You mean that if the craft is using all his power, it could explain that less power is used to communicate with the RC and reduce the range i could get the signal ?

Hi,

Oke, just curious why the app made 2 flightlogs.

Guess there is always power left to stay in contact with the RC, i fly sometimes to 3 % batt for test and no problems.

Th orange marker * [ 49.30630000, 1.23501000 ] is just a calculation i made, taken into account drift speed, heading, height ect.
So i believe it landed on ground and not in the water.

* search in the line > last postion to marker, mayby just bit left of that line.
Hope you will find it. (and if you find it, hope you had and if not mayby an idea to put your phone number etc on the SD card )

cheers
JJB

JJB* Posted at 6-7 04:34
Hi,

Oke, just curious why the app made 2 flightlogs.

... just curious why the app made 2 flightlogs.
i fly sometimes to 3 % batt for test and no problems.

There's a new log in case of loosing connection and RTH, it happened to me a few times.
Today I tested low batt behaviour and my Mini performed auto landing exactly at 3% (after very long flight), it was possible to control the AC (stop the descent with up stick and move sideways but as soon as I was not pushing up it landed).

virtual Posted at 6-7 08:26
... just curious why the app made 2 flightlogs.
i fly sometimes to 3 % batt for test and no problems.

thanks for your info, never experienced this myself  (yet...)  ;-)

JJB* Posted at 6-7 08:49
thanks for your info, never experienced this myself  (yet...)  ;-)

It's better to have no experience with it!
The second log started in air (after regaining connection and canceling RTH) so I had 2 logs for1 flight (one take-off and one landing).

virtual Posted at 6-7 09:19
It's better to have no experience with it!
The second log started in air (after regaining connection and canceling RTH) so I had 2 logs for1 flight (one take-off and one landing).

Still strange, as in this flight (post #1) i see 2 more full disconnects and the data is still in one log...

So do not understand when yes and when no logs are split in more than one

JJB* Posted at 6-7 10:58
Still strange, as in this flight (post #1) i see 2 more full disconnects and the data is still in one log...

So do not understand when yes and when no logs are split in more than one

I think if the connection RC to the drone is interrupted for a longer period of time, so much longer than 11 seconds. I've had it before and the first log showed a flight time of 0:00 to 2:54 and the second one didn't start with a flight time of 0:00 but 3:50. It was also interesting that at the beginning of the second log the info "Setting new Return-To-Home altitude to 55m (180 ft). Data Recorder File Index is 10 ...." was generated. When I viewed both tracks in Google Earth, 300 meters were missing, which corresponds to the time between the end of the 1st log and the start of the 2nd log.

Hello there Clément. I am sorry to read and to know that your DJI Mavic Mini was lost. Since this unfortunate event happened I would recommend you to contact our DJI support team at https://www.dji.com/support?site=brandsite&from=nav for further assistance.  We have a professional team that will do there best to check what happened to the said drone and will give out the best resolution for this issue. Again I am sorry for the trouble and please stay safe always.

jonny007 Posted at 6-7 12:28
I think if the connection RC to the drone is interrupted for a longer period of time, so much longer than 11 seconds. I've had it before and the first log showed a flight time of 0:00 to 2:54 and the second one didn't start with a flight time of 0:00 but 3:50. It was also interesting that at the beginning of the second log the info "Setting new Return-To-Home altitude to 55m (180 ft). Data Recorder File Index is 10 ...." was generated. When I viewed both tracks in Google Earth, 300 meters were missing, which corresponds to the time between the end of the 1st log and the start of the 2nd log.

Mayby, in this log 3x een disconnect, first 15.4 secs, second 17.6 secs, third 29 seconds.  

So perhaps a value > 30 seconds?

cheers
JJB

cpetit Posted at 6-7 04:22
Concerning the fact i have 2 flight records, i do not have any explanations. but i am sure i did not restart my phone or the RC. I think i maybe just lost connection at this time.

Just to mention that I made the same flight a few minutes before, same weather conditions, and no problems at all... including no connection problem. And i believe that if i did not have this connection problem I could have saved the drone and made an emergency landing. You mean that if the craft is using all his power, it could explain that less power is used to communicate with the RC and reduce the range i could get the signal ?

Second thought, can you upload your first part of this flight ?

cheers
JJB

Just to be clear to all mavic Mini owners.

Batteries drop their voltage and their ability to deliver current as they deplete.

Taking off in the wind you may be able to fly reasonably well when the batteries are full. At 50% battery they lose 50% of their ability to deliver current to spin the motors.

At a certain battery percentage the wind will be too powerful for the mini to make forward progress. It will blow away in the wind.

You need to take this into account in your flight planning.

On a windy day do not run your batteries down. Keep plenty in reserve, don't fly below 50% battery usage.

Cheers
  

JJB* Posted at 6-7 22:50
Second thought, can you upload your first part of this flight ?

cheers

Hello,

https://www.phantomhelp.com/logviewer/4S831LGPZ31T0A0GL0P8/

Here is the first log. As you can also see, there is no wind warning until I reach the distance of 330m from the home point (approx 1000ft). That's is also where problems began when i came back.

I have not been successful in my research but I left a message in peoples letterbox who lives around your estimated landing point ! Hope I'll get some news today or tomorrow.

Thanks

bjr981s Posted at 6-7 23:32
Just to be clear to all mavic Mini owners.

Batteries drop their voltage and their ability to deliver current as they deplete.

Hiya,

i have tested my MM in windy conditions, and no difference in a 100% battery or 30% battery.
Speed and Motor RPM the same, so loosing 50% of power at 50% batt level; don`t think you are correct.

But at the end of the battery level range DJI will reduce power output.

Agree with you that a MM is a bit "underpowered", so take the wind warning serious and don`t fly if wind speed > 8 m/s. (but i my test it can handle much more...)  just be cautious and don`t take the risk, ecspecially if you fly over water....

cheers
JJB

bjr981s Posted at 6-7 23:32
Just to be clear to all mavic Mini owners.

Batteries drop their voltage and their ability to deliver current as they deplete.

Is it something specific to mavic mini or other mavic drones ? Has DJI communicated about it ?

In my case, you are right, things became to go wrong at around 50% of the battery capacity. But it seems to also have an impact on wifi as at this point I have experienced a lot of disconnections and almost no video feedback (or really laggy) which would have enable me to land anywhere.

JJB* Posted at 6-8 00:04
Hiya,

i have tested my MM in windy conditions, and no difference in a 100% battery or 30% battery.

OK Battery lesson required.

Batteries have a C rating. The C rating defines the maximum amount of Current the battery can deliver per maH of the battery.

E.g With a C rating of 10 a 5,000mah battery can deliver a max current of 20 x 5 = 100A without the battery suffering a brownout. ( Brownout is a sudden loss of voltage)

A 10C 2500mah battery can deliver a max current of 20 x 2.5 = 50 Amps.

There is plenty of tutorials on YouTube on this.

So a 5000mah battery discharged to half 50% is a 2500mah battery and can deliver 50 Amps max. And so forth.

At 10% it can deliver 10 Amps.

Now depending on the actual load on the motors that defines how much current it will draw based on the KV of the motor. KV is the number of revs it will try and achieve per volt supplied. This then needs to be distributed for each of the 4 motors.

So At 10% charge it will deliver 2.5 Amps to each motor.

The design of the craft needs to take discharging batteries into account. The craft will be designed to only require a C rating to perform all the way down to a low %.

Not a big Issue you just design and put in larger batteries to cover it.

But when you design a craft to a weight limit 249g you have to sacrifice something.

The Mini does not have big enough batteries to fight the wind at lower discharge levels.

QED.

   

cpetit Posted at 6-8 00:08
Is it something specific to mavic mini or other mavic drones ? Has DJI communicated about it ?

In my case, you are right, things became to go wrong at around 50% of the battery capacity. But it seems to also have an impact on wifi as at this point I have experienced a lot of disconnections and almost no video feedback (or really laggy) which would have enable me to land anywhere.

This is a factor for all RC models that are Battery powered. I also fly Fixed wing and Helicopter electric models. It's well known in the hobby world in flying clubs. Drones have introduced a complete "Do it Yourself" model that allows a novice to buy a drone and fly. You don't have to join a club, learn about RC models, and fly with supervision and exams (Club) to get your solo wings.

I see a lot of learners advising learners on anecdotal evidence that is not correct. I try to point things out when I see them.

Batteries are the most misunderstood technology in the drone world. Manufacturers try and build to this, but not all. DJI do pretty well with AutoDischarge on LiPos in storage.

But still people get confused with the Battery Level indicator on the APP and what it really means.

Here is a quick set of facts on DJI batteries and the App % Meter.

• 0% on the indicator does not mean the battery is at 0% charge. It is above fully discharged. (DJI) leave a real % in reserve but not much.
• The indicator is only accurate if you have discharged your batteries completely and then recharged. (As per the DJI manuals requiring you to do this every 3 months)
• Following the DJI recharge every 3 months damages your batteries.
• The longer you leave the full discharge and then charge the more inaccurate the indicator will be. You will see the indicator showing 50% batteyr and then suddley go down by a 1% or more per second until it gets to zero. Hopefully it will autoland and not be above water. .
• The majority of DJI batteries are LIHVs high voltage LiPos. Do not use 3rd party LiPo chargers they will damage your batteries. Use only the OEM charger.
• DJI batteries will self discharge over time, down to damaging levels. (this is one reason that they ask you to recharge every 3 months.) The monitoring action on the batteries continually discharge the batteries slowly over time, and will drop to damage levels.
• If you check your batteries regularly do not trust the % lights on the battery. Turn the battery on to get a real % level.
• Activating the new DJI batteries, does not actully do anything other than set the monitoring service to on. They do this becasue of the reasons above. Its so the batteries do not drain while in the DJI stores warehouses.
• If you want to get an indication of your real battery status, check the batterty cell voltages in the app. At 100% charge they will be at 4.4 Volts per cell (LiHV) at flat they will be at 3.4 Volts per cell. So 10% for each .1 of a volt. roughly. Its not 100% linear. Also as the battery discharges it will subtley discharge faster for the same flight performance.
• None of this applies directly to the Mavic Mini. It uses Lion batteries that have differeent voltage levels and chargactaristics. It is to be nothed that LiHVs, LiPos, have a greater power storage capacity per gram than Lions. But Lions do not require the same management disciples and can be treated much more roughly.
  

Cheers

bjr981s Posted at 6-8 00:28
OK Battery lesson required.

Batteries have a C rating. The C rating defines the maximum amount of Current the battery can deliver per maH of the battery.

Thanks, but it all depends how much draw a MM needs for its performance.

if DJI designed this drone to fly within specs from 100% batt to 10% batt than there is no problem.

DJI will infor the user with a low output message not at 50% batt level but much later.

cheers
JJB

I have a question, just out of curiousity and since I am very very newbie reading flight logs etc
Between 13:12 and 13:15 the Mini goes in negative altitude up to -3ft, which I assume means it flew below the RTH level. From a quick look in google maps I cannot see any elevation around the lake, so how is it possible?

The flight ended tragically because basic safety rules were ignored.

Among which:

- Flying in a too high wind, even before the flight started the wind conditions of about 12 m/s (and 14 m/s gusts at ground) were a big NO
https://www.ventusky.com/?p=49.277;1.364;10&l=wind-100m&t=20200606/1500
- Flying beyond vLoS and too far away in especially demanding conditions.
- Failing to set a minimal RTH (it's unlikely it would have helped but 30m over water means that even more energy was spent to climb into higher winds) for the above water surface flight.-
- Failing to set CH and frequency appropriate to the environment, random disconnections in plain view of the homepoint and getting closer suggest that probably 2.4 GHz was auto-selected. 2.4 GHz you should consider can have random busy patterns depanding on Wi-Fi usage of those using it. Meanwhile, despite having less throw the 5.8 GHz (CE) is far less susceptible of being affected by random frequency usage and is usually outside home routers Wi-Fi range.
I think it's importat to underline these facts so that other users don't repeat the same mistakes.

For my understanding the flight could have been savable until very late, selecting HOVER for loss of connection option and piloting the Mavic Mini along the wind direction as much possible to shore (at an altitude of about 20m max, to clear the trees), getting closer by running along the perimetral lake trail in case of disconnection before the MM entered land. I think one could have recovered the Mavic Mini doing a normal landing (I usually palm land mine) or after an auto-lading for battery depletion.

ThalisGr Posted at 6-8 02:33
I have a question, just out of curiousity and since I am very very newbie reading flight logs etc
Between 13:12 and 13:15 the Mini goes in negative altitude up to -3ft, which I assume means it flew below the RTH level. From a quick look in google maps I cannot see any elevation around the lake, so how is it possible?

Barometric sensor is not that accurate, it can vary during flight.
Minus 3 feet and VPS height that moment plus 1 feet, so it was flying real close to the water.

Guess the take-off postion was bit higher than the water level too.

cheers
JJB

bjr981s Posted at 6-8 00:28
OK Battery lesson required.

Batteries have a C rating. The C rating defines the maximum amount of Current the battery can deliver per maH of the battery.

There are misleading information here. Mavic Mini uses SAMSUNG 18650 25R 2500mAh Lion cells with 20A max load (C) rating, If it was true that at 10% batt left there's 1/10 of ability to handle the load, all Minis had to fall from the sky at 10%, as the battery wouln't handle the load needed to spin all motors, run reciever, operate gimbal ect. It is the safety feature that battery must handle rated load for the whole discharge cycle, otherwise battery is overloaded and demaged soon.
Cell voltage is droping down through the discharge cycle so the rev range is partly limited* with low battery (MM can fight the wind worse) and becase of this the current drawed by motors is lower at low batt level.
* It should be well calculated and EMU probably never or rarely uses full throttle (all the revs available) so it's different to one motor AC where can be perfomance drop significant.

JJB* Posted at 6-8 03:05
Barometric sensor is not that accurate, it can vary during flight.
Minus 3 feet and VPS height that moment plus 1 feet, so it was flying real close to the water.

Yes sure the take off position was above the water let's say 50 cm to 1 m approx.

here is the last video i get from the drone where it went really close to water
https://drive.google.com/file/d/1N1HeFx-Y1RJ0R1PePdY3DrAKl3kiSnLr/view?usp=sharing

@m80116
I did not see the drone at the end of the flight so it was difficult to save it, with all the trees you can see on the video  around the lake on this part (I tried to run along the trail around  the lake but never get a signal but sure i could have anticipate a bit the problem if i had known)
Concerning the signal, i did not try to change the frequency but i do think that there is really few wifi networks around the lake

m80116 Posted at 6-8 02:54
The flight ended tragically because basic safety rules were ignored.

Among which:

Concerning wind, I think your website is just forecast and is not based on real observation. Real observation (closest airport) shows approx 15 knots of regular wind (8,3m/s) with some gusts.

With the wind you mention, my girlfriend I was trying to film would not have been able to sail with the sail size she had

https://fr.windfinder.com/report/rouen/2020-06-06

Let's also note that this airport is at an altitude of 157m and the lake not far from sea level.

cpetit Posted at 6-8 03:56
Concerning wind, I think your website is just forecast and is not based on real observation. Real observation (closest airport) shows approx 15 knots of regular wind (8,3m/s) with some gusts.

With the wind you mention, my girlfriend I was trying to film would not have been able to sail with the sail size she had

I think it is about as much as the website reported for ground speed, where airport observations are done. And although 100m is some 70odd meters in excess of what the actual final flight height was, better safe than sorry right ? It's far more likely the wind at that altitude over a lake wasn't too much different than that at 100 meters (land even empty one still has many more features to slow air down).

virtual Posted at 6-8 03:42
There are misleading information here. Mavic Mini uses SAMSUNG 18650 25R 2500mAh Lion cells with 20A max load (C) rating, If it was true that at 10% batt left there's 1/10 of ability to handle the load, all Minis had to fall from the sky at 10%, as the battery wouln't handle the load needed to spin all motors, run reciever, operate gimbal ect. It is the safety feature that battery must handle rated load for the whole discharge cycle, otherwise battery is overloaded and demaged soon.
Cell voltage is droping down through the discharge cycle so the rev range is partly limited* with low battery (MM can fight the wind worse) and becase of this the current drawed by motors is lower at low batt level.
* It should be well calculated and EMU probably never or rarely uses full throttle (all the revs available) so it's different to one motor AC where can be perfomance drop significant.

You need to read my post in detail and not skim.

Yes I identified that the Mini was Lion and behaves subtly differently.

But then explain why in the wind on low battery warning you get the Drone advising it does not have enough power for the props?

I pointed out in my verbose post that the motors have a KV. That is the revs the motor can spin per volt. (Actually it’s the revs the motor wants to spin at per volt [with no load] but dependant on the supply of current to get there).

The actual current drawn from the battery, is dependant on the resistance the motor is experiencing pulling air through the props.

As you may know max torque of an electric motor is at 0 revs. ( And max current draw if stalled) Why if a motor stalled it goes up in flames.

This torque action is why Electric Vehicles have significant acceleration.

When the voltage starts to drop as the battery depletes, the revs of the motor / props drop so the FC pushes the motor harder by raising it throttle request.

This is what we call in the Electronics Industry a Positive Feed back Loop. They never end well.

To address your comments individually.

SAMSUNG 18650 25R 2500mAh Lion cells with 20A max load (C) rating

20A is not the C rating of this battery. It is the max current you can draw before thermal runaway, and the battery is destroyed.

If it was true that at 10% batt left there's 1/10 of ability to handle the load,

Yes that is correct, you are confusing my description of the actual batteries ability and characteristics with DJI Battery level %. As I pointed out in the post This is an arbitrary scale defined by DJI. It does not actually represent the real state of the battery.

It is the safety feature that battery must handle rated load for the whole discharge cycle, otherwise battery is overloaded and demaged soon.

I don’t understand what you are saying here? It is non sequitur. Do you think your battery example can output 20A at .1% of charge. Do some research on Batteries on the net. I can assure you that discharging a Lithium battery past its threshold will destroy the battery.   

It should be well calculated and EMU probably never or rarely uses full throttle (all the revs available) so it's different to one motor AC where can be perfomance drop significant.

I do not know what you are trying to say here. As I explain above about motor KV all the revs are not available as soon as the battery starts to discharge.

Anyhow, as I was trying to explain to everyone, flying the Mini in high wind on low battery levels is outside of the performance envelope of the mini design. i.e it has a departure.

Cheers

cpetit Posted at 6-8 03:56
Concerning wind, I think your website is just forecast and is not based on real observation. Real observation (closest airport) shows approx 15 knots of regular wind (8,3m/s) with some gusts.

With the wind you mention, my girlfriend I was trying to film would not have been able to sail with the sail size she had

Real observation (closest airport) shows approx 15 knots of regular wind (8,3m/s) with some gusts.

Well, max speed at P-mode is 8 m/s (manual sais Max wind speed resistance 8 m/s), so it looks like pushing the limits...

bjr981s Posted at 6-9 06:08
You need to read my post in detail and not skim.
Yes I identified that the Mini was Lion and behaves subtly differently.
But then explain why in the wind on low battery warning you get the Drone advising it does not have enough power for the props?

20A is not the C rating of this battery.
Yes it is, 20A means 8C discharge rating for the 2500mAh cell.



Do you think your battery example can output 20A at .1% of charge
Reliable battery of course can output guaranteed power (that is the meaning of C rating BTW) without damage, it is clear that fresh full battery can output 20 Amps a few minutes long while discharged battery (at 10% for example) only for a few seconds because then there's no power left to supply...

virtual Posted at 6-10 00:52
20A is not the C rating of this battery.
Yes it is, 20A means 8C discharge rating for the 2500mAh cell.

Sorry, you can't work backwards to determine a C rating.

Please also explain in your theory of batteries, why the C rating relates to the mah capacity?

Your description of how a battery works is false. Batteries are not like a container of water. The don’t have a constant flow until they run out.

In that same logic the batteries would have the same voltage from full to empty, then suddenly drop to zero.

You cant get around Ohms law.  

Please do some research on batteries before you comment further. You just confuse those that I am trying to inform.

I also suggest that you do some research on Batteries Internal resistance that will assist your understanding when coupled with Ohms Law.

It will also explain why batteries show different voltages from a Load to no load. i.e. in flight drawing current and after flight no current.

A final question for you. Why do you think that Mavic Minis get errors in their logs saying not enough power and slowly descend in the wind on low battery?

Cheers

By the way, do you know which criteria is used by the MM to trigger a high wind alert ? Does this depend on the battery level ? and does the wind direction vs drone direction has an impact ? (ie is it different if the wind and the drone are going in the same or in the opposite direction?)

You can try to find your drone bu using other drone looking down

bjr981s Posted at 6-10 04:00
Sorry, you can't work backwards to determine a C rating. Please also explain in your theory of batteries, why the C rating relates to the mah capacity?

Your description of how a battery works is false. Batteries are not like a container of water. The don’t have a constant flow until they run out.

Interesting posts. It makes sense. I know people that have said they fly on half used batteries they haven't depleted in one flight try to fly another day with the 50% left battery and have voltage issues and this explains why. I always fly with fully charged batteries so have never had an issue with it.

cpetit Posted at 6-10 12:40
By the way, do you know which criteria is used by the MM to trigger a high wind alert ? Does this depend on the battery level ? and does the wind direction vs drone direction has an impact ? (ie is it different if the wind and the drone are going in the same or in the opposite direction?)

It does matter which direction the drone is flying in relation to the wind.

It's the amount of force required to maintain position and the angle of tilt required to counteract the wind.

The max tilt angle is fixed. If you are flying with the wind, then you are assisted by the wind. In flying as a cross wind (either left or right of the drone direction it will tilt into the wind to hold position or course. In flying into the wind if you have max tilt to hold with the wind then you can't tilt any further and no forward progress will be made.

If you are unsure just hover and check the angle of tilt required to hold position.

Sports mode will allow an increase in max tilt angle. And can save you from a blow away. It's important through to reduce altitude as far as you can safely before engaging sports mode.

If you start to get warning on Max power. Then pick a place to land as safely as possible where the drone is at that time.  Stretching it further in sports mode with minimal forward speed will just flatten the battery and it may land in an inappropriate location.

To exactly answer your question:

High wind warning is purely driven by the tilt angle imposed by the wind to hold course or position.

The Max power warning is that it does not have sufficient resources to maintain stability and or progress required by command.

Cheers

cpetit Posted at 6-10 12:40
By the way, do you know which criteria is used by the MM to trigger a high wind alert ? Does this depend on the battery level ? and does the wind direction vs drone direction has an impact ? (ie is it different if the wind and the drone are going in the same or in the opposite direction?)

It does matter which direction the drone is flying in relation to the wind.

It's the amount of force required to maintain position and the angle of tilt required to counteract the wind.

The max tilt angle is fixed. If you are flying with the wind, then you are assisted by the wind. In flying as a cross wind (either left or right of the drone direction it will tilt into the wind to hold position or course. In flying into the wind if you have max tilt to hold with the wind then you can't tilt any further and no forward progress will be made.

If you are unsure just hover and check the angle of tilt required to hold position.

Sports mode will allow an increase in max tilt angle. And can save you from a blow away. It's important through to reduce altitude as far as you can safely before engaging sports mode.

If you start to get warning on Max power. Then pick a place to land as safely as possible where the drone is at that time.  Stretching it further in sports mode with minimal forward speed will just flatten the battery and it may land in an inappropriate location.

To exactly answer your question:

High wind warning is purely driven by the tilt angle imposed by the wind to hold course or position.

The Max power warning is that it does not have sufficient resources to maintain stability and or progress required by command.

Cheers

bjr981s Posted at 6-10 04:00
Sorry, you can't work backwards to determine a C rating. Please also explain in your theory of batteries, why the C rating relates to the mah capacity?

Your description of how a battery works is false. Batteries are not like a container of water. The don’t have a constant flow until they run out.

Maybe You should do some research before You "try to inform" others, because the theory that half-charged 5000mA battery is 2500mA battery and can handle (not deliver BTW) only a half of current draw is completely wrong. C rating is related to overall capacity only, so the max current draw (Amps You can draw from battery) is the same for full and discharged battery.
I did quick google search for You: "C Rating is an indicator of the continuous discharge rate of a LiPo. It allows users to easily calculate the maximum constant current you can draw from the LiPo pack safely without harming the battery.
Max Current Draw = Capacity x C-Rating
For example, if you have a 3S 1000mah 20C LiPo pack, your safe max current draw would be 1000ma x 20C = 20A.
You might wonder, can I draw more amperage than the above figure (i.e. higher the 20A given in the example)? You could, but it’s not recommended. Discharging a battery too quickly is bad for the health of the battery."

Here You have the answers.

Then You need to understand that current draw is generated by motors (plus reciever, gimball, recording electronics ect.) and it's about the same with full battery and with discharged battery (in the same flight situation). C rating informs You what power You can safely use, so the overall current draw of all electronics in drone (motors, EMU, reciever, gimball, recording device, lights ect.) has to be significantly lower than C rating of battery. Samsung battery is 20A rated which means that max current draw of the Mini in the air is lower than 20 Amps, that's all.

Not enough power drops were definitely not caused by "not enough C" battery. MM Battery voltage drops during discharge cycle from 8+V to aprox. 6,5V, ESC regulates motors RPMs through voltage change. When the battery is discharged (and voltage is lower), there was probably no voltage left to increase RPMs for angle requested by EMU to fight the wind which made errors with strange reaction as there was no reason to drop suddenly. That's my theory but I'm not a drone builder. It should be sorted now by fw update.

virtual Posted at 6-11 09:37
Maybe You should do some research before You "try to inform" others, because the theory that half-charged 5000mA battery is 2500mA battery and can handle (not deliver BTW) only a half of current draw is completely wrong. C rating is related to overall capacity only, so the max current draw (Amps You can draw from battery) is the same for full and discharged battery.
I did quick google search for You: "C Rating is an indicator of the continuous discharge rate of a LiPo. It allows users to easily calculate the maximum constant current you can draw from the LiPo pack safely without harming the battery.
Max Current Draw = Capacity x C-Rating

You're wrong. The power isn't a constant. Try wearing down a battery to two lights, wait a day then fly again the next day on a half used battery and see what happens. You get multiple voltage warnings etc. This is well documented and there are multiple topics from people asking why they had power errors starting a flight on a partially used battery.

Power is not a constant but not because of the amp which decrease, but because of the voltage which slowly decrease. The "C" rating is a constant over the whole discharge curve, and not linked to the remaining capacity of the battery, and hopefully!
Cells are used (for Lipo) from 4.2 to 3.5 or 3.6. Power being Voltage*Intensity, if the voltage decrease, the power decrease as well.
What increase the problem is the cells internal resistance which will decrease the voltage while the amps increase.
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-25R%202500mAh%20%28Green%29%20UK.html
You can see that the capacity decrease with high current load, but the battery is able to sustain the current until reaching 2.9 V