Was just thinking about an experience I had yesterday where my compass went totally bad in the middle of a flight.

  

I keep reading that when calibrating an IMU that you have to be on a flat surface and not move it. Fair enough because those items will affect the Gyroscope and Accelerometer (2of3 IMU inputs). But nothing is said about items that may affect the compass (magnetometer) during an IMU cal. It would seem to me that if I calibrate the IMU near a source of compass interference that it will affect the overall calibration of the IMU and could easily cause flight issues. After all, the compass is the third input into the IMU so if it is reading incorrectly it should have a negative impact on the proper calibration of the IMU and possibly cause fly aways?  

  

What am I missing here guys?

  

Hi Mochorm. As I see it your kind of answering your own question. As in, I would and have calibrated the IMU, I did it as far as possible from any possible electromagnetic interference (the furthest the cables would allow from the computer) on a flat surface and leave alone till it's done. I have had no issues at all. Before I did this I did have an issue as it flew off of it's own accord when ever I input yaw. Calibration corrected this. Doing it as above your removing/reducing the possibility of there being a problem. Hope this helps

Good day sharplkie, ya I'm throwing this out there because of my experiences and reading about numerous compass errors and flyaways. So I did some research on IMU's. Hence my question to DJI and the forum as to the current calibration procedure, as it seems flawed and could be contributing to people having compass issues!

I'm not an expert on the subject and would have thought this would be addressed by DJI, but it appears as though it has not? So I would like someone from DJI to comment and tell me/use why calibrating the IMU near compass interference is an acceptable  thing to do ? If it's not acceptable then I would expect the manual to say so and DJI to say as much when recommending IMU calibrations.

P.S. Sharplkie, just curious why you are calibrating your IMU with a USB cable attached? The rare earth magnet in that external hard drive sitting on your desk  is very powerful, so get your bird too close to one could really mess up the magnetometer (compass)!

mochorm Posted at 2016-7-11 13:46
Good day sharplkie, ya I'm throwing this out there because of my experiences and reading about numer ...

He may have a P2 vision/plus

all calibrations were usb connection via the Vision Assistant on PC/MAC.
IMU cal doesn't calibrate the compass , that is done as a separate process usually outdoors.


if you have the interference notice when doing IMU simply move it to a clear clean signal location, even a few inches or a foot can help

mochorm Posted at 2016-7-11 18:46
Good day sharplkie, ya I'm throwing this out there because of my experiences and reading about numer ...

Spot on with Kirk2579 above, I do have a P2 Vision plus hence the usb connection for calibration of the IMU. Being a newbie to the DJI world I didn't know that things were different on the later models sorry.

kirk2579@aol.co Posted at 2016-7-11 11:52
He may have a P2 vision/plus

all calibrations were usb connection via the Vision Assistant on PC/ ...

Never said the IMU cal, calibrated the compass. However the compass data is used during the IMU calibration sequence.

If you calibrate the IMU near compass interference you will have a garbage IMU cal. Which could easily lead to error's and fly aways.

How do I know if I have interference when doing an IMU cal? There is no mention in any DJI documentation to check for interference when doing a IMU Cal.

So one would assume from the manual that as long as the surface is flat and you don't move the bird, that is all the matters. I'm saying that you also need to ensure you are not near anything that could affect the compass while calibrating the IMU.

I think for absolute certainty the aircraft must be on a extremely flat level surface. If doesn't hurt to be free from metal either although I've done plenty of IMU calibrations with my aircraft on my desk next to the computer monitors.
You just need to make sure there are no vibrations.

But to be safe, calibrate the IMU on your kitchen table or island..

mochorm Posted at 2016-7-11 16:27
Never said the IMU cal, calibrated the compass. However the compass data is used during the IMU ca ...

true about not being near interference like monitors, speakers etc....
when I tried it too close one day it was very clear that I was not in good spot...

that's what I was referring to about moving the quad a bit..
sometimes as little as inches or a foot can move you to interference free area.

good luck and have fun flying!

what happened when you say the compass went totally bad in flight?

what did it do ?
what did you do to fix/correct the totally bad compass in flight?

sharplkei@gmail Posted at 2016-7-11 15:53
Spot on with Kirk2579 above, I do have a P2 Vision plus hence the usb connection for calibration of ...

no sweat on differences. Had a couple p2 and a plus as well, awesome quads for sure.
It was a bit different though going to P3 , no wifi, no extender, usb cable to tablet etc.

good luck and have fun flying!

kirk2579@aol.co Posted at 2016-7-11 18:07
what happened when you say the compass went totally bad in flight?

what did it do ?

Actually it was very uneventful !
Compass error flickered in a couple times and I heard Atti mode. But the error went away. So I was bringing it closer to home, as this is not normal. Then the compass status went full red error and I heard switching to Atti mode, and it stayed on. Toggled the mode switch to atti mode and watched my Xcopter moving slightly with the wind, nothing extreme. Brought her home and landed it.
Calibrated the compass and continued to fly just fine.

mochorm Posted at 2016-7-12 13:07
Actually it was very uneventful !
Compass error flickered in a couple times and I heard Atti mode ...

thanks,

putting it into the atti mode position was best thing you could have done, many don't when SHF.
it don't need the fancy stuff so much when your driving manually!

good luck and have fun flying!