Does P4P have to be level during IMU Initialization? If yes can somebody explain why please? How important it is?

Yes, It will maintain your drone/s in 90* flight, and keep a straight horizon in your recorded videos.


RedHotPoker

Yes, you should make sure it is PERFECTLY level otherwise your videos will be tilted

RedHotPoker Posted at 2017-1-9 22:36
Yes, It will maintain your drone/s in 90* flight, and keep a straight horizon in your recorded videos.

In that case, what's the purpose of Gimbal Auto-Calibration or IMU calibration?

I thought the AC just had to be completely still during startup. I quite often have mine in a slight (but noticeable) angle during startup but always stable and I don't see any gimble alignment issues in my videos. Everything looks level. I understand IMU calibration needs to be done exactly level and I thought that was when it created a datum. Is there some official advice from DJI somewhere?

kykphantom Posted at 2017-1-10 00:12
In that case, what's the purpose of Gimbal Auto-Calibration or IMU calibration?

Aloha kyk,

     Your P4P needs to be stable to go through the launch process.  For your IMU calibration your P4P has to be very level, as in use a level to make sure it is level.  If your images do not turn out level, then you have to calibrate the gimbal with the P4P level again.

     But, as regards your question, it is a real problem if you start up your Phantom and it falls over because it was not stable.  If you look at your camera when your Phantom is initializing, you will see that even if it is not level, the camera will end up level and the camera view will be level.  If it is not level, you got some calibrating to do.

Aloha and Drone On!

(MUST JUST FIRST SAY ON DJI NEW EQUIPMENT CALIBRATIONS SHOULD ONLY BE DONE WHEN PROMPTED)


IMU "Inertial measurement unit"

As far as I see it, IMU calibration on a level surface updates a table of values the flight controller software uses as a reference for a level stationary hover. From there the craft responds predictably to flight commands.  It also likely measures any sensor noise and thermal drift so that these technical imperfections are accounted for when using IMU sensor data in flight. - this is likely why there must be no vibrations during the calibration process.


Bad IMU calibration could cause drift and attitude issues as the flight controller fights to hold the craft in what it thinks is the correct attitude as opposed to the correct physical attitude.


The IMU usually has 2 types of sensors – angle and acceleration and in turn 3 sensors of each type measuring in the X,Y and Z axis. These sensors can, through vibration, aging, impact etc, drift in their response over time and thus an IMU calibration will establish a new reference for the IMU’s level/stationary state that the flight controller can work with to restore stable flight.


Think of calibration as the bringing back into line the measured craft attitude with the true physical craft attitude.


As to how often an IMU calibration is needed, I wouldn’t like to say; certainly after any impact or if there are suspicions the craft can’t hover in a level attitude in a windless environment. Also after a firmware update is a good opportunity just in case the stored values get corrupted or are incompatible with the later firmware.


Its also good to mention that the IMU is the reason why you are able to shut off the motors using just the throttle down command when on the ground. The IMU reads that the aircraft is unable to move any further, and after three seconds it determines that is has officially landed and can shut off the motors safely.

hallmark007 Posted at 2017-1-10 06:54
(MUST JUST FIRST SAY ON DJI NEW EQUIPMENT CALIBRATIONS SHOULD ONLY BE DONE WHEN PROMPTED)

Very good description of the IMU and why and when a calibration is needed.

However, the original question is: Does the drone have to be level during IMU initialization (i.e. the first few seconds after the drone is switched on)?

kykphantom Posted at 2017-1-10 08:24
Very good description of the IMU and why and when a calibration is needed.

However, the original question is: Does the drone have to be level during IMU initialization (i.e. the first few seconds after the drone is switched on)?

Apologies, answer is yes as the manual explains when starting your aircraft you should be on a level surface and the same for landing, this is obviously best procedure, but if it is slightly off level it will have little if no effect on your IMU or gimbal .

No i think he means since the new p4p has a different imu calib then the p4 should the spot be level...and i say yes when going thru the new imu calibration i made sure my spot was level. Also after calib i did a gimbal calib on that same level surface...one thing to note i did let aircraft get cold outside for 20 mins then did calib....def helps with imu warm up times when going to fly

hallmark007 Posted at 2017-1-10 08:32
Apologies, answer is yes as the manual explains when starting your aircraft you should be on a level surface and the same for landing, this is obviously best procedure, but if it is slightly off level it will have little if no effect on your IMU or gimbal .

I can't find in the manual where it says takeoff and landing should be on a level surface. On P60 it says "Place the aircraft in an open, flat area". Flat is completely different to level. I understand how the IMU works and agree that IMU calibration MUST be done on a completely level surface but am still looking for official documentation from DJI. I haven't had any issues when powering the AC on when it is not level.

I have always been strict about a dead level surface for IMU and gimbal calibration. Then check IMU for confirmation.

I still wonder about having a quick IMU warm up when flying in colder weather?  Yes, it's good to do your IMU and initial gimbal calibration with a chilled drone.
It certainly reduces the time getting ready to take off after turning on the drone. Though I still go through a preflight checklist, so the time saving isn't all that important to me.
Plus when flying in cold weather, it's important to let everything warm up for a couple minutes anyway. So what temperature should the drone be, to calibrate the IMU, when planning winter flights?
If it was too warm, it may take forever for the preflight warmup. Just something I thought about.

The other thought was in preparing our props for winter flights. ;-) What about storing props in the freezer? Getting them used to being under 0*C.


RedHotPoker

Hendo Posted at 2017-1-10 11:57
I can't find in the manual where it says takeoff and landing should be on a level surface. On P60 it says "Place the aircraft in an open, flat area". Flat is completely different to level. I understand how the IMU works and agree that IMU calibration MUST be done on a completely level surface but am still looking for official documentation from DJI. I haven't had any issues when powering the AC on when it is not level.

Sorry Hendo but I think you will find the meaning of flat is,  having a level surface; without raised areas or indentations. I.e. An ice rink needs to be completely flat.

RedHotPoker Posted at 2017-1-10 12:03
I have always been strict about a dead level surface for IMU and gimbal calibration. Then check IMU for confirmation.

I still wonder about having a quick IMU warm up when flying in colder weather?  Yes, it's good to do your IMU and initial gimbal calibration with a chilled drone.

"The other thought was in preparing our props for winter flights. ;-) What about storing props in the freezer? Getting them used to being under 0*C. "
I imagine the props warm up during flight due to friction with the air and flexing, I doubt they will stay below 0 for long, at least not the important bits that flex.

In any case, their material should be fine down to -40 so I wouldn't worry.

Nigel_ Posted at 2017-1-10 12:25
"The other thought was in preparing our props for winter flights. ;-) What about storing props in the freezer? Getting them used to being under 0*C. "
I imagine the props warm up during flight due to friction with the air and flexing, I doubt they will stay below 0 for long, at least not the important bits that flex.

I was thinking of deep freezing an old prop, and checking it for flexibility, or actual brittle nature.

I would tend to think, a spinning prop in minus 0* temperature, would get even colder with the wind chill it creates on its journey.  It isn't going to warm up from friction in dry cold air. Unlike a car tire spinning on ice.


RedHotPoker

Unlike my P4 and P3P, the P4P prompts you to lay the drone over in various positions during IMU calibration. Previously I use a small level platform since the drone stayed in one place on its landing skids during the entire IMU calibration process. The platform is not big enough to lay it over like the screen prompts show. So, do I need to get/make a bigger platform that is perfectly level or will a normal hard floor work (tile/wood/concrete)?

Cobra that is what i did. I just made a bigger level space then performed imu calib ....worked great

Can a DJI representative explain what the P4P is doing during IMU initialization, so we can understand why it should be on a flat level?

RedHotPoker Posted at 2017-1-10 12:35
I was thinking of deep freezing an old prop, and checking it for flexibility, or actual brittle nature.

I would tend to think, a spinning prop in minus 0* temperature, would get even colder with the wind chill it creates on its journey.  It isn't going to warm up from friction in dry cold air. Unlike a car tire spinning on ice.

That would be an interesting test, always good to know these things instead of guessing based on theory.  I doubt you will notice much difference at -18 freezer temperature, I think they are made of nylon and if you look up the properties of nylon then it doesn't  react much to cold before -40 and in normal use is happy to go to far colder temperatures than that.  Yes it does loose flexibility, but not much.

Doesn't wind chill require evaporation?  So since the blades are not wet they will not cool due to wind chill...

RedHotPoker Posted at 2017-1-10 12:35
I was thinking of deep freezing an old prop, and checking it for flexibility, or actual brittle nature.

I would tend to think, a spinning prop in minus 0* temperature, would get even colder with the wind chill it creates on its journey.  It isn't going to warm up from friction in dry cold air. Unlike a car tire spinning on ice.

It's my understanding that wind chill has little to no effect on inanimate objects. The only difference would be if there were moisture on the surface or the object were hotter than the environment for some reason.

As far as turning on the aircraft on a not-level surface (in preparation to flying), I have done that many times. The AC will upon turning on the motors try to level it self somewhat with higher rpms than normal idle but I have had no problems with flight. Calibration of course is a different story. Flat and level.

KM5RG-Robert Posted at 2017-1-11 08:14
As far as turning on the aircraft on a not-level surface (in preparation to flying), I have done that many times. The AC will upon turning on the motors try to level it self somewhat with higher rpms than normal idle but I have had no problems with flight. Calibration of course is a different story. Flat and level.

Similarly, for more than a year now, I turn the AC on holding it in the air and take off from my hand. Never had a problem either with flight or hovering or gimbal horizontal level.

However, IMU calibration and gimbal auto-calibration, always level.

kykphantom Posted at 2017-1-11 08:25
Similarly, for more than a year now, I turn the AC on holding it in the air and take off from my hand. Never had a problem either with flight or hovering or gimbal horizontal level.

However, IMU calibration and gimbal auto-calibration, always level.

If you don't mind me asking how can you hold the aircraft in the air in one hand and start the motors, ??

I have hard time doing hand launch because inability to start motors, makes my tablet fall off of the radio....  so i do not hand launch - I land in my hand only. I guess if u had a place to put the radio down and then use your left hand to either do auto-takeoff on the tablet or use the whole hand to do the start motor stickshake... otherwise it's a bit more troublesome....

As for IMU, I do mine on a little table outside with a piece of glass on it that I can level - it is also nice to do imu calibration while the drone is rather cold, and the ambient temp is cold too.. as it would seem that whatever temp you do your calibration at, that is the temp the drone want's to be at before allowing you to fly - hence the "aircraft warming up" - which i rarely got before i did my own imy calibration.....

Phantomski Posted at 2017-1-11 10:41
I have hard time doing hand launch because inability to start motors, makes my tablet fall off of the radio....  so i do not hand launch - I land in my hand only. I guess if u had a place to put the radio down and then use your left hand to either do auto-takeoff on the tablet or use the whole hand to do the start motor stickshake... otherwise it's a bit more troublesome....

As for IMU, I do mine on a little table outside with a piece of glass on it that I can level - it is also nice to do imu calibration while the drone is rather cold, and the ambient temp is cold too.. as it would seem that whatever temp you do your calibration at, that is the temp the drone want's to be at before allowing you to fly - hence the "aircraft warming up" - which i rarely got before i did my own imy calibration.....

Hand catching not a problem , but hand launching sounds a bit dangerous, might be that I have small hands. Lol

Remember the old times when RC flyers used to have that shelf thing on their neck, and they would just put the radio on it? That is what we need these days!

hallmark007 Posted at 2017-1-11 10:48
Hand catching not a problem , but hand launching sounds a bit dangerous, might be that I have small hands. Lol

Hand launching is not difficult if you use a neck strap for holding the RC.

kykphantom Posted at 2017-1-11 13:15
Hand launching is not difficult if you use a neck strap for holding the RC.

Ok gotcha, will have to be careful I don't hang myself. Lol