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IMU Calibration
4411 24 2015-6-16
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JerryLaurence
Second Officer
Flight distance : 1588 ft
United Kingdom
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Is it necessary to do IMU calibration after a firmware update? I have a new Inspire 1 and don't want to mess around with IMU if it's not necessary...

Thanks.
2015-6-16
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FictitiousPerso
Second Officer

United Kingdom
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I do all my calibrations after a firmware update and just compass every first flight. Works for me no issues so far!

Remember and calibrate on a level surface.
2015-6-16
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Skywolf007
Second Officer
Flight distance : 2758875 ft
Slovakia
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I do IMU calibration after firmware update.. Its not that hard.. Just remember to keep the inspire stationary on a leveled surface 10-15m before you start IMU calibration...

About Compass - I do calibrate only when needed, or when I travel to a new place to shoot some videos..

Better safe than sorry
2015-6-16
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tapboxer
lvl.4
Flight distance : 824672 ft
United States
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I did not do a EMU cal. after the last firmware upgrade, but i did check the EMU and it said it was okay... if its not broken....
2015-6-16
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JerryLaurence
Second Officer
Flight distance : 1588 ft
United Kingdom
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Is there an official DJI recommendation about this?
2015-6-16
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FictitiousPerso
Second Officer

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JerryLaurence Posted at 2015-6-16 18:43
Is there an official DJI recommendation about this?

Doesnt make any difference! It's called peace of mind and takes seconds!
2015-6-16
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JerryLaurence
Second Officer
Flight distance : 1588 ft
United Kingdom
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I guess my caution comes from Phantom discussions where, if the surface is not absolutely level, you could irreversibly worsen the aircraft's flight characteristics. Or maybe that's a myth...
2015-6-16
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FictitiousPerso
Second Officer

United Kingdom
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I see your point but how hard is it to take a level and check you have a level surface?
2015-6-16
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JerryLaurence
Second Officer
Flight distance : 1588 ft
United Kingdom
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Well, from the Phanom geeks, level is never level enough and a sub mm difference will through things out of balance. I don't know if that's true but would like to know what the DJI gurus say.
2015-6-16
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SAFAERIALS
Second Officer
Flight distance : 93146 ft
Dominican Republic
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I my opinion its always better to do the IMU calibration after the firmware and then check every now a then the values to see if it's needed again
2015-6-16
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dbeck
Second Officer

United States
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There are crazies on this forum that go to absurd lengths (building NASA quality devices) to insure that the Inspire sits totally zero level on their surface prior to IMU!  Nonsense, I say, a gigantic waste of time.  A garage floor or work bench surface properly leveled with a bubble level is all that is needed. And then when the IMU is calibrated a simple check in the APP menu..."Check IMU" will determine if the IMU needs calibrating again.  This over zealous contsatnt resetting of the IMU is harmful!
2015-6-16
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PeteGould
Second Officer

United States
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JerryLaurence Posted at 2015-6-16 20:32
Well, from the Phanom geeks, level is never level enough and a sub mm difference will through things ...

Sub-mm differences?  "Irreversibly" worsen flight characteristics (not just until another IMU calibration)?  Someone is having fun scaring people.  If that were true, IMU calibration would not be an available customer function as it could only be done in a lab.  Heck, there are undoubtedly sub-mm differences in landing gear leg length, so even on a 100% level surface in a lab the aircraft probably won't be 100% lab-spec level.

I generally use a carpenter's level to check before doing an IMU or gimbal calibration, but there have been times on location when I had to do an IMU cal unexpectedly and used a downloadable "level" app on my iPad.  I can pretty well guarantee that's not accurate to the sub-mm level, though it's still pretty darn good.  The bird flew perfectly.

Yes, there are some issues with Inspire (and Phantom) flying behavior, and people are looking for things to pin the blame on.  But you're infinitely more likely to have a problem because you didn't recalibrate the IMU when you should have than because your carpenter's level wasn't accurate enough.

As to what the gurus say - just look in your manual.  It says to do the calibration on a "level" surface.  No huge cautions in red boldface type about sub micron accuracy or the specter of permanently ruining your aircraft.  The average owner doesn't even read this forum and likely does their IMU cal on a desk or table without even using a level.  If it was such an utterly critical thing that it could only be done on a laboratory grade dead-level surface, do you not think it would be extensively covered in the manual?

2015-6-16
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nilsblix
First Officer
Flight distance : 10122100 ft
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If my IMU values is fine I do not calibrate. If my compass value is fine I do not calibrate.
This is just me - I have over 300 flights with my Phantom and Inspire with no issues ( except from pilot errors )
2015-6-16
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FictitiousPerso
Second Officer

United Kingdom
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dbeck@promobox. Posted at 2015-6-16 21:25
There are crazies on this forum that go to absurd lengths (building NASA quality devices) to insure  ...

Perfect choice of words "Crazies" lol
2015-6-16
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w1der
Second Officer

Sweden
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As we never know exactly what the new firmware is doing to the Inspire (what parameters are changed) I always do the IMU cal after updates.
I already have the bird standing there on my living room table anyways, and don´t wanna risk having to do the IMU calibration out doors where it could be hard finding a level surface and also time consuming.

I have been searching online for answers about this ... There are a lot of opinions!
My own opinion is ...
Fly aways isn´t caused by "bad calibration" of either compass or IMU ...
At most a bad calibration would cause some drifting.

Fly aways is caused by "ERRORS", either "faulty parts" or "f*cked up data" in the software (or from pilots that can´t fly whit GPS drop out).   
2015-6-16
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SimplePanda
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JerryLaurence Posted at 2015-6-16 19:01
I guess my caution comes from Phantom discussions where, if the surface is not absolutely level, you ...

Total myth.

Use an iPhone / iPad levelling app or a simple bubble type carpenters level you can get at a hardware store for a couple of bucks. I use a small plastic one.
If the calibration is off, do it again. You can't damage the IMU with a bad calibration.



2015-6-16
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SimplePanda
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PeteGould Posted at 2015-6-16 21:25
Sub-mm differences?  "Irreversibly" worsen flight characteristics (not just until another IMU calib ...

This.

DJI aircraft aren't perfect, but nothing is. People use the imperfections to ask "Why did it crash itself?" rather than "What could I have done differently?" or "What did I miss?".

Just today there is a "Fly away" thread in which the operator goes from total stand-still on the ground to damn near 300 feet in the air without even so much as hovering the aircraft and eyeballing it in low hover to make sure nothing is unusual. Guess what? Compass is obviously out of calibration and the gimbal is basically leaning over within moments. You'd think the fact that the FPV is showing a 30 degree roll on the image would be an indication that something is amiss, but does he land?

Nope. He takes it up to almost 1000 feet and then is shocked (shocked I tell you) when he has control issues. But that's a "fly away", of course (even though he did get it back in one piece).

If you get in your car and the brakes only half work backing out of your driveway, it's a maintenance problem you need to address immediately. In the UAV world, people just shrug that off and immediately b-line for the autobahn for some reason...
2015-6-16
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robvelez
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United States
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What does IMU stand for on the Phantom?? Inertial Measurement Unit?
2015-6-18
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frank320
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Singapore
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SimplePanda Posted at 2015-6-17 00:42
Total myth.

Use an iPhone / iPad levelling app or a simple bubble type carpenters level you can ge ...

I second using some kind of level. Your Iphone compass has a simple level which should be good enough.
Here's what i do to calibrate IMU.
1) Place the inspire on a flat surface, both front and side should be level - i.e zero degree pitch and roll.
2) Use the iphone level, with iphone rested flat on surface and camera facing the nose of the inspire, ensure level - 0 degree
3) Then, with iphone rested flat on surface and camera facing the side of the inspire, ensure level - 0 degree
4) Start the IMU calibration process and minimize any movement or vibration around the inspire

Once IMU calibration is successful, the values should look like these:
Gyroscope: X=0, Y=0, Z=0, mod = 0 (they should be all zero since the inspire is stationary)
Accelerometer: X=0; Y=0, Z=1.0, mod = 1.0 (X=Y=0 since the inspire was stationary and flat on the ground and has no acceleration in the X and Y axis. Z = 1.0 for the vertical 1g of gravity)

With that, you should be good to go.

As a bonus, since your IMU has just been calibrated on a level surface, run the Gimbal Auto calibration immediately after. Kill 2 birds with one stone, as they say.

I only calibrate after every firmware update, or if the IMU values differ from above when i place the inspire on a flat surface.


2015-6-18
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dennis
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FictitiousPerso Posted at 2015-6-16 16:51
I do all my calibrations after a firmware update and just compass every first flight. Works for me : ...

I follow the same process and have had the same successfull results
2015-6-18
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rladbwnd84
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South Korea
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Tip: The post by the administrator or moderators shield
2015-6-18
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SimplePanda
First Officer
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robvelez@gmail. Posted at 2015-6-18 22:47
What does IMU stand for on the Phantom?? Inertial Measurement Unit?

Correct; IMU = Inertial Measurement Unit.

An IMU, specifically, is a hardware unit that integrates a variety of sensors (though not always the same combination / type of units). The Phantom / Inspire / A2 etc would have barometers (air pressure measurement for altitude), accelerometers (to measurement movement force and tendency) and gyroscopes (to measurement angle of orientation).

Many IMU units also include a magnetometer (compass), but on the Phantom this unit is actually on the leg of the aircraft to remove it from the interference rich environment of the flight controller / chassis. I'm pretty sure the compass and GPS (positional) sensor are read together as a separate unit from the IMU based on the way everything is wired (compass connects to GPS module, GPS module connects to flight controller via a PMU).

As a total aside, modern IMU's are super accurate.
https://www.raspberrypi.org/real ... th-the-minimu-9-v2/
2015-6-19
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SimplePanda
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frank320 Posted at 2015-6-18 23:51
I second using some kind of level. Your Iphone compass has a simple level which should be good enou ...

Note that an IMU mod of 0.99-1.01 is "in spec" so people shouldn't be upset if their mod is drifting between these values. Even the occasional flash of 1.02 is fine as long as it's very brief and rare. If you start seeing >=1.02 or <=0.98 consistently, recalibrate. Otherwise, you're good.
2015-6-19
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Grimtheviking
lvl.4
Flight distance : 2909193 ft
United Kingdom
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I do all new calibrations after a firmware update and compass before most flights,especially if in new location.
IMU calibration on a desk top that I have never had a spirit level on,,,
150 flights and only firmware bugs problems, "touch wood"
Brilliant machine,

Regards
Mike.
2015-6-19
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fans7769bc8c
lvl.1
United States
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Hi I have a phantom 3 professional and also Inspire 1. Can you use the Phantom 3 professional controller to be the slave for your Inspire 1.
2017-5-15
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