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Re: [Paparazzi-devel] Motor mixing saturation - max offset unbounded

From: Felix Ruess
Subject: Re: [Paparazzi-devel] Motor mixing saturation - max offset unbounded
Date: Tue, 23 Apr 2013 23:17:48 +0200


> OK as long as it is known as not handled.

Well, this still needs to be properly done. Would be great if you could test at least the mitigating fix I proposed in the previous mail.

So in case of hitting both limits, only apply the lowering of the throttle instead of simply applying both offsets as it is done now.

> The IMU current calibration feature is nice, I would just like to point out that there are AHRS systems (such as GX3 from Microstrain) which allow you to do only static calibration (so called soft-iron calibration), not a dynamic one with changing current. Then such a drift can occur.

True, if you already get the calculated attitude from the AHRS. If you only get sensor data and compute the attitude in paparazzi, you can use this...

> I don't know how to handle it properly at the moment, but fortunately the motor mixing is an issue only during very slow take-off. Once you hit ~40% of thrust, the autopilot has enough control authority so this saturation doesn't occur.

The "fix" proposed should (partially) help. As a workaround you can also try lowering the factors in the YAW_COEF (and increase the gains accordingly). Since the incoming roll/pitch/yaw commands are bounded this will also bound the motor commands you get from yaw this way.

Cheers, Felix

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