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IMU CCALIBRATION TEMPERATURE QUESTION!.. PLS HELP !
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gerardorejeg
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Hi again,,, this time I have a question about the IMU CALIBRATION TEMPERATURE.   I read that calibration of thr IMU SHOULD BE DONE in a cold environment.  Well  last time ive done mine was about 76 degrees .. The IMU IS TAKING NOW LONG TO WARM UP.  

My question is,  if I do the calibration when it gets colder around here  with the endeavor to get the IMU TO  WARM UP FASTER,,, how will that set the IMU to warm up to a lower temperature to start with,,, if the actual calibration takes bout 5-10 minutes....  even if the environment around me is colder than 76 degrees...  by the time that the calibration is completed the IMU WILL BE ALREADY AT 76 DEGREES!!!!   Do you understand what im getting at?    or is it just me? CAN ANYONE EXPLAIN THIS PLEASE?

THANKS IN ADVANCE
2016-6-2
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RedHotPoker
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You can chill down your drone in front of an air conditioner or do as I just did today, stick it in the fridge without the battery for twenty minutes.
Have the RC on and Go app with the IMU calibration page open, replace the battery and turn on the drone, when the camera stops, tap Calibrate IMU.
I do the Gimbal calibration directly after.
When you do these calibrations while the drone is cold, it reduces the initial warm up period. Often helps eliminate crooked horizon too.
Perhaps "some" new pilots who are prone to panic attacks, also need the Chill Pill as well? hahaha
For these minor emergency outbreaks, "Stick your head in the freezer, while the drone cools off in the refrigerator"... ;-$ doctors order!?! Haha


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2016-6-2
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gerardorejeg
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RedHotPoker Posted at 2016-6-2 13:01
You can chill down your drone in front of an air conditioner or do as I just did today, stick it in  ...

Thank you,,, also.. I live in a second floor...CAN I CALIBRATE it on the floor of my second floor? or it has to be strictly outside at ground level on a flat surface?
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RedHotPoker
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Calibration of your drone's IMU and Gimbal is mostly done indoors, just fine.
But you need to do the Compass out of doors, away from any ferrous (magnetic) metal or electrical interference.

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2016-6-2
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gerardorejeg
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RedHotPoker Posted at 2016-6-2 14:22
Calibration of your drone's IMU and Gimbal is mostly done indoors, just fine.
But you need to do the ...

Thank  you,, so the fact that I will do the IMU calibration on the second floor  about 15 feet from the ground wont have any effect when i fly it outside taking off from the ground ? Like the altitude wont get messed up?  
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RedHotPoker
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No, that is not calibrated each time you turn on the drone.
But the drone will establish the home point, and know where it is, when you power up...
People have flown from well below sea level, and others have taken off from a mountain top.
Even though the IMU and compass were calibrated at a much different altitude, the drone will behave and operate just fine.


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gerardorejeg
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RedHotPoker Posted at 2016-6-2 15:00
No, that is not calibrated each time you turn on the drone.
But the drone will establish the home po ...

Thanks a lot.. I really appreciate it
2016-6-2
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RedHotPoker
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It's good to know, once you do a proper IMU & Compass calibration, you shouldn't need to do another one, unless you move to a new location, a couple of hundred miles away.
Just notice the MOD values, check what those numbers are in the app, and see that they are within a safe-flying parameter.

RedHotPoker
2016-6-2
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dobmatt
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Almost everything related to "cold IMU calibration" was explained here, but you need to understand that the chilled drone must be calibrated in warm environment. Another word the IMU calibration of cold drone in cold environment will not work, resulting in pre-programmed warming time before flight. Remember to keep the battery warm, make sure the calibrating surface is truly level and - most importantly - don't move around during 10 minute calibration. Heavy truck passing by, kids running around table, even your dog can fool sensitive instruments.
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Kneepuck
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gerardorejeg Posted at 2016-6-2 14:05
Thanks a lot.. I really appreciate it

You do absolutely want to make sure the place you do the imu calibration is very level and stable though.  Important.   And you can download a free app for your device that is a level.  Lots of them in fact.
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RedHotPoker
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Yes, or a handy bubble level can be used as well.
It's true that many household floors, counter tops and tables aren't always as flat, as they may appear to be to us, visually.
But as close to 90* as humanly possible, is fine too. This isn't rocket science folks. Ha

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2016-6-2
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dobmatt
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RedHotPoker Posted at 2016-6-3 11:09
Yes, or a handy bubble level can be used as well.
It's true that many household floors, counter top ...

You wouldn't believe how many rocket scientists out there is testing payload with bucket of water on rope attached to a leg just to watch how the bird is desperately trying to maintain balance and overcome increasing pendulum effect before spectacular crash. Surely $1000 worth YouTube footage ...

BTW, I couldn't hold my laugh reading your recommendation to hold the table surface at 90 deg.. Seriously, IMU calibrating process is critically important, therefore I will suggest to employ some tools to set the surface as level as humanly possible indeed. Naturally this must be done on X and Y axis, which will set Z axis perfectly perpendicular to leveled surface. This IS rocket science ! Once done properly is good forever ... or until rough landing ... or until another FW update ...
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endotherm
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RedHotPoker Posted at 2016-6-3 13:09
Yes, or a handy bubble level can be used as well.
It's true that many household floors, counter top ...

I'm sure level surfaces, calibration of guidance systems etc IS very important in rocketry too, so IT IS rocket science!
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rodger
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You can let it come to room temp. and you will be fine. You can do it on any floor in your home. Be sure to have it on a flat level surface and that it does not move at all. The IMU determines hoe level the Phantom is in flight and controls drift. If your Phantom is tilted and drifting while in the air the calibration os off.
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gerardorejeg
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rodger Posted at 2016-6-3 07:38
You can let it come to room temp. and you will be fine. You can do it on any floor in your home. Be  ...

thanks alot brother
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rodger
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Not a problem. Happy flying.
2016-6-3
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Athlon
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For exact IMU calibration I ´ve created this table.
The feets are individually adjustable. No metal...only glas and plastic....

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Aardvark
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You could always go Here for complete peace of mind
2016-6-3
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RedHotPoker
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endotherm Posted at 2016-6-2 22:54
I'm sure level surfaces, calibration of guidance systems etc IS very important in rocketry too, so  ...

You wouldn't know true rocket science if it bit you on the arse. So get off the pot, ok. ;-)
Please, let's not even go there. Unless you have degrees and shingles on the wall. Hahaha
Here's a perfectly level table work top for you...

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2016-6-3
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Not A Speck Of
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I use glass to level as well, but I just put it on top of the 4 rotors (without props) and put the level on the glass. If it's not level, I move it around the table until it is. Use objects under the landing legs if you must.

Thanks to whomever mentioned this method in the past week or two.

Just a note, since it hasn't been said in this thread yet: a lot of people do not recommend putting your drone in a fridge. Cooling it with air from an AC unit is one thing, but the fridge can be too moist.

A lot of people, including myself, or okay just doing it in the morning before the day heats up. In summer, put it in a room that has windows opened so that the room cools during the evening. In winter, letting it sit on an covered porch or patio to cool off is fine.

And do not cool down the battery.

As others said, be sure that the remote is already fired up and ready to start the calibration within seconds of firing up the craft.
2016-6-3
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RedHotPoker
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Frost free fridges are pretty dry inside, both the refrigerator section and ice box freezer portion.
They work very similar to what a dehumidifier does.
And twenty minutes in there won't collect enough moisture to matter.

I like to complete my three calibrations right after a firmware update, and take it out to fly as soon as possible. ;-)

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2016-6-3
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AG0N-Gary
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dobmatt Posted at 2016-6-2 21:44
Almost everything related to "cold IMU calibration" was explained here, but you need to understand t ...

Where in the world did you get that idea?  Yes, chill it down and do it while it is cold.  Keep the battery warm, but don't take so long that the Phantom warms up before you are done with IMU calibration.
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dobmatt
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AG0N-Gary Posted at 2016-6-4 08:38
Where in the world did you get that idea?  Yes, chill it down and do it while it is cold.  Keep th ...


I must admit that I'm confused ... I can't see any sense of cooling down the sensors and keeping the drone in cool environment during calibration. This should convince the drone that indeed it's cool out there and the system must be warmed up before take off. At least my logic dictates such scenario. I did just that once and it resulted with prolonged warm-up time. Chill the craft outside during frosty days and bring it inside for calibration, throw warm battery in and start the calibration immediately - that's the procedure described many times by others. It works charmingly. Naturally the fridge option is for warm climates and lonely pilots (you wouldn't dare to do it with your wife in proximity). Correct me if I'm wrong, please.
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AG0N-Gary
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dobmatt Posted at 2016-6-4 03:15
I must admit that I'm confused ... I can't see any sense of cooling down the sensors and keeping t ...

My point was, don't warm it up, after you go to the trouble of cooling it down, until you calibrate it! It takes about 10-20 minutes to do the calibration, during which time, it is probably warming itself up, unless they disable the IMU heater during calibration.  The idea is to calibrate it while the IMU is cold, so it doesn't take so long to get up to the calibration temperature when it is warming up.  Ideally, I'd like to calibrate like I did the first time I did it cold.  It was 17F outside.  I set it out on the level spot and let it cool down for about an hour before, then I took the warm battery out, plugged it in and fired it up.  I went back in the house so I could stay warm, leaving the bird outside, and initiated the calibrate.  Warmup after that was VERY fast.  More recently, I had to do it around 45 degrees, since it isn't getting as cold over night now.  The idea is to do the calibration at a lower temperature than you normally fly in so you don't have to wait so long for it to warm up.

The actual temperature that you calibrate isn't as important as the fact that you do it lower than normal ambient when you fly.  I just take it outside in the early morning, right before dawn, normally the coolest part of the day, and do it then.  I watch the forecasts, so I can choose one of the cooler mornings of the week.
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drag line
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I decided to do a IMU calibration last night as it was taking several minuets to get pass the warm up period. I took my P3P and with the battery removed placed it on top of the floor vent  with the AC running for about 20 minuets and then tilted so the air was blowing toward the battery compartment. I took my controller and had everything ready to go. Placed the P3P on my glass top table put in the battery and connected and started a IMU calibration. Happy to say took it out this morning for a sunrise flight over the lake and it was almost a instant and said it was ready for flight. I will make sure to do this every time I have to calibrate the IMU.
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dobmatt
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AG0N-Gary Posted at 2016-6-5 04:47
My point was, don't warm it up, after you go to the trouble of cooling it down, until you calibrate ...

Thank you for your reply. Still, the scientific reasoning for this procedure escapes my logic, although it provides correct results somehow. DJI-Ken once responded " Don't think too much, just do it. Trust me: it works." Whatever ...
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Aardvark
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RedHotPoker Posted at 2016-6-3 23:51
Frost free fridges are pretty dry inside, both the refrigerator section and ice box freezer portion. ...

Problem is not in the fridge, it's when you take it out, would just then act as a condensation plate for any moisture in the air. You could always test with a glass in fridge, take it out and see what happens.
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RedHotPoker
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"Panic in Detroit", i hope no one was watching... ;-)

It has Never bothered me, but I live in a dry climate without much humidity in the tranquil air surrounding my homestead.
Besides, if it was a big deal, no one would do it... Hahaha

I have not had any problem from a 15 minute refrigerator cool down, then place the drone on the floor to calibrate IMU and gimbal.
As I stated, frost free fridge, dry humidity in the air. Still having no problems since day one. And no shell cracks around screw pockets or any other places.
I wouldn't leave in in there over night, and then pop it into a steam bath or sauna... Haha
You should see what a Nikon D800 will withstand!! Hehe

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Rnfaust
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Athlon Posted at 2016-6-3 21:14
For exact IMU calibration I ´ve created this table.
The feets are individually adjustable. No metal ...

Now that's German engineering.
I made a imu and gimbal calibrating table from a scrap of MDF (medium density fiberboard 3/4"). I added 3 screws and nutserts for adjustment. I use a digital level for x-y but it's shown here using an iPhone app. It couldn't be more stable - except for RedHotPoker's picture of course.
PS: I find a 3 point adjustment much easier to deal with than 4 points.
Table.jpg
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Airspace Explor
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Rnfaust Posted at 2016-6-4 15:58
Now that's German engineering.
I made a imu and gimbal calibrating table from a scrap of MDF (medi ...

So the spongy footpads on the landing gear are all the same thickness when weighted by the drone?

And you level the baseplace with the drone in place?
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Airspace Explor Posted at 2016-6-5 07:12
So the spongy footpads on the landing gear are all the same thickness when weighted by the drone?

...

WOW the lengths some people are going to,,, its almost like a cult following.

When your drone was born in china what did the Chinese do to set the IMU i wonder????
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Rnfaust
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Airspace Explor Posted at 2016-6-5 07:12
So the spongy footpads on the landing gear are all the same thickness when weighted by the drone?

...

The pads seem even enough for this guy.
I level the base first - not that it really matters.
I think the IMU measures the gyroscope and accelerometers, so besides being level, there can't be any vibration or movement when calibrating.
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AG0N-Gary
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dobmatt Posted at 2016-6-4 16:41
Thank you for your reply. Still, the scientific reasoning for this procedure escapes my logic, alt ...

You may be thinking that you are calibrating it to a specific temperature.  You're calibrating it to a minimum temperature.  I'll go out on a limb and repeat something I think I understood correctly from someone else's explanation.  The sensors are actually miniature mechanical devices that detect and measure changes in direction.  This is where I go out on a limb.  The devices are membranes of flexible material that can flex due to inertia.  That flex can be measured and fed to the control system and corrected for.  If the material is not flexible enough (like if it is too cold), they can't properly detect movement.  Keeping it warm enough is the job of the IMU heater.  If you calibrate at a high temperature, the controller will wait until it gets to that temperature to assume it is warmed up enough.  That's what is going on when it says 'warming up'.  Calibrate it cooler, and it will 'warm up' quicker.  Of course, there is a minimum temperature.  What is it?  I don't know.  As I said, I did it at 17F.  It flew beautifully after that.  I once did it at 70F.  It took forever to warm up and flew the same.

I hope this has helped you understand, and also hope it is accurate enough to 'pass inspection' by others who may understand it more.  
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dobmatt
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AG0N-Gary Posted at 2016-6-5 08:50
You may be thinking that you are calibrating it to a specific temperature.  You're calibrating it t ...

The more I'm thinking about this "chilled drone" IMU calibration procedure, the more I'm afraid we are messing with the very idea of calibrating. For some reason this approach is not mentioned in official DJI instructions of any kind. It's just home cooked way to full the drone and get rid of warming-up time, which may be necessary and crucial for proper functioning of the sensors on main board. After all it's not a big deal and maybe I'm trying to split the hair for no reason whatsoever...
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Airspace Explor
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dobmatt Posted at 2016-6-4 01:15
I must admit that I'm confused ... I can't see any sense of cooling down the sensors and keeping t ...

The sensors that are used for IMU have outputs that vary with temperature.

So here's what I surmise is going on.

A temperature sensor is used to compensate for this IMU sensor variation with temperature.

So it's best to calibrate when the sensor temperature is constant to eliminate that one variable.

If the electronics in the shell are warmer than ambient (for example after a fast run on a warm day with a hot battery), the sensor will cool during calibration.

Likewise, if the electronics are cooled to below ambient before applying power, the electronics will heat the sensors to a temperature above ambient along with all else in the shell.

So letting the UAV sit without power for 25 minutes in a room at a temperature comfortable for humans before calibration should be fine.

UPDATE 2016.06.06 - One likely explanation for the advise to calibrate ASAP after power-up is that, without the air circulation from the rotors, the temperature in the shell will rise above normal in-flight operating temperature. So you'd want to do calibration while the temperature of the relevant electronics are close to that in flight. Note that this explanation is not verified by DJI.
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AG0N-Gary
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dobmatt Posted at 2016-6-4 20:35
The more I'm thinking about this "chilled drone" IMU calibration procedure, the more I'm afraid we ...

Cold calibration is backed by the DJI techs on this forum.
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Airspace Explor
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AG0N-Gary Posted at 2016-6-4 19:46
Cold calibration is backed by the DJI techs on this forum.

Depends on what is meant by 'cold'.

I take 'cold' to mean the same as when checking the inflation of your car's tires.

For areas that experience seasonal variations in temperature, should one calibrate the IMU once there is a significant change in daytime temperature?
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RedHotPoker
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Dry Ice, my good man. The drier the better...
For a real chiller, liquid nitrogen... ;-)

RedHotPoker

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Athlon
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Rnfaust Posted at 2016-6-5 00:58
Now that's German engineering.
I made a imu and gimbal calibrating table from a scrap of MDF (medi ...

Also a nice idea :-)
2016-6-5
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dobmatt
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AG0N-Gary Posted at 2016-6-5 10:46
Cold calibration is backed by the DJI techs on this forum.


I'm not sure about this ... We don't really know if DJI-Ken or DJI-Paladin are a "tech" persons, although I've no reason whatsoever to question their knowledge or authority. All we know for sure they're here to watch, administrate and help, they're able to transfer our issues to related departments in DJI structure and get things going into assumingly right direction ...

The way I see the so called "cold" IMU calibration issue? Someone, some time ago, discovered this way to get rid of annoying "Warming Up" display and be able to take off immediately after powering the aircraft. Everybody is blindly following the recipe in order to gain ... what actually? 2 or 3 minutes? C'mon ... All I want to know is the reason for warming up, and the potential consequences of eliminating this process before taking off. Maybe this fooling "cold" IMU calibrating procedure is causing some erratic behaviors of drones reported by many, who'd f...k really know?
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