Tongala

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Mag_transform values and calibration sequence
« on: January 27, 2018, 12:33:52 am »
Hi have a few questions.

But first I wish to say this is not about how to calibrate (that is covered well in wiki and GCS) but about values and sequence.

I also wish to say I have a 280mm quad with DJI gps and Revo that is very well behaved in gps modes ,PH, VR (although need to play around with tuning) and auto land.

First mag_transform values, I read elsewhere (can't recall where and can't find it again) that values should be between 0.85 - 1.05.

Mine are 1.17889........1.16664........1.24831 and have been 1.16113365,0,0,0,1.14655042,0,0,0,1.22270429
Both worked fine.

1. I understand that these values can give an indication of accuracy of mag calibration.
        My question is what range of values should I be aiming at and why?
        I always calibrate out in the open over oplink.

2. Calibration sequence,this is what I do.
     thermal followed by board level then gyro, next
     set home location then accelerometer then mag. calibrations.

Question is, does anybody have thoughts on order and why?

3. Every now and then board seems to lose mag calibration after sitting for a couple of weeks and need to
        re- calibrate. Has happened at least 6 times in the last year.
Any idea why?

Finally had a quick look at Next (Next Downloads) before I dive in does anyone know if mag calibration or gps algorithms have changed ? Maybe this is not the right place to ask this question.

Thank you.

f5soh

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Re: Mag_transform values and calibration sequence
« Reply #1 on: January 27, 2018, 04:59:14 am »
Scales values depend in which mag sensor you are using, around 1.2 is normal for a DJI GPS and will be around 1.6 on a onboard Mag for Sparky2.

HomeLocation is needed for Accelerometer calibration (for gravity) and Mag calibration for the expected magnetic field vector according to the world mag model stored in board.

Redo a Mag calibration will be not needed except if magnetic activity from earth changed a lot or more likely something changed under the frame. Can be a new accessory, battery, lipo saver around.

Next uses the same calibration process but own improved gps algorithms (INS13/INS13+CF).
Complementary+Mag+GPS can be used for navigation/GPS assistance now. This assumes you erase the board and start with new numbers or take a look at current Jira for new settings values.

Tongala

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Re: Mag_transform values and calibration sequence
« Reply #2 on: January 27, 2018, 10:02:46 pm »
Thanks for reply, will pay more attention to any small changes to/under quad.

I'm aware that home location must be set before Accelerometer and Mag calibration but does it matter if I do Accelerometer first then Mag calibration or Mag first then Accelerometer calibration?

f5soh

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Re: Mag_transform values and calibration sequence
« Reply #3 on: January 28, 2018, 01:54:30 am »
There is no prerequisites between Accelerometer calibration and Mag calibration so the order doesn't matter.