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Re: [Paparazzi-devel] Problems with magnetic field

From: Ewoud Smeur
Subject: Re: [Paparazzi-devel] Problems with magnetic field
Date: Wed, 26 Aug 2015 13:43:42 +0200

Hi Thomas,

Indeed there was a possibility of getting a non-real number, I think it should be fixed with
The addition of an offset would indeed be nice, as you show an offset at 0 throttle. Actually, a better current estimation would be better solution, maybe we can create a define MILLIAMP_AT_ZERO_THROTTLE.

From your picture it looks like all power is running through the pcb below the autopilot. It *might* be better to have wires as you can twist them (voltage and ground) to reduce their magnetic field Also, it might improve if they run on the other side of the quad instead of underneath the autopilot.



> Date: Wed, 26 Aug 2015 12:04:50 +0200
> From: address@hidden
> To: address@hidden
> Subject: [Paparazzi-devel] Problems with magnetic field
> 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]
> [2]
> [3]
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> Paparazzi-devel mailing list
> address@hidden

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