[Paparazzi-devel] Problems with magnetic field

[Thomas Kolb]

Hello everybody,

I'm currently trying to do the current calibration for my quadrocopter.
The calibration for the Earth magnetic field was done with motors
turned off and has worked quite well (the yaw angle looks correct in
all directions). With motors on, there is serious drift in the yaw
angle (40° to 80° difference).

As I don't have a current sensor, I have set MILLIAMP_AT_FULL_THROTTLE
= 60000, which is a rough estimation from the motor specification. Then
I ramped the throttle up and down according to the wiki. You can find a
screenshot of the log in [1] and the log data in [2].

The current estimation does not seem to distinguish between motors off
and on, but idle (estimated current is 0A after starting the motors).
However, the magnetic field is influenced quite heavily already by the
idle current, which should really be about 2A. This change in the
magnetic field already causes the yaw angle estimation to drift for
about 40°.

Is it possible to give some “idle offset” to the current estimation, so
that “motors on” means 2A minimum?

Another problem is that the current estimation “overflows” when
reaching the maximum. This could be related to my transmitter, which
can also set the throttle to 102% (according to the GCS). What would be
the best approach to fix this?

In case it helps, [3] is a photo of the setup I'm currently using.
Maybe you could give me some hints where the magnetic field might come
from. It might be possible to improve on it through hardware changes.

Thank you for any advice.

Greetings

Thomas


[1] http://temp.tkolb.de/paparazzi/mag_cal.png
[2] http://temp.tkolb.de/paparazzi/mag_cal_log.zip
[3] http://gallery.tkolb.de/Fotos/Basteln/Quadrokopter/IMG_4868.JPG.html