Airspeed sensor influence on FBW_A

Hi All,

I have tuned my APM (without airspeed sensor) in a Skywalker for good FBW_A flight according to the documentation. Roll control is crisp, maintains ~45% on full-stick and doesn't lose altitude. I have also done a number of AUTO missions successfully (some several km's long).

I've now added an airspeed sensor and with no changes besides enabling airspeed, FBW_A is behaving badly. Entering and exiting a roll is very 'bouncy' and untidy. It looks like the roll axis is bouncing, but there could be pitch in there also. Once held in a turn it is fairly stable.

Given that it is FBW_A mode and there is no target airspeed or target altitude, why does the behavior change? Do I need to re-tune the servo pids?

Thanks,

Dave

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Replies

  • It's just a thought as I am unfamiliar with your particular setup, but the position of your pitot-static tube may play a role. 

  • A quick look at Attitude.pde suggests that the servo pids *do* need re-tuning as the servo output is scaled based upon what speed info the APM has.

    When there is no airspeed sensor, it uses the throttle servo output as an indicator, when there is an airspeed indicator (and the reading is > 0) it appears to use the airspeed.

    This makes sense as it did behave as though the RLL2SRV pid was way too high, I shall try and reduce it and see if that fixes my problem.

    It would be great if someone could confirm this logic though :)

    Dave

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