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Re: [Paparazzi-devel] puzzles on the control loops of fixedwing

From: Eduardo lavratti
Subject: Re: [Paparazzi-devel] puzzles on the control loops of fixedwing
Date: Thu, 7 Aug 2014 10:54:16 -0300

I think aileron of throttle is used because the motor generate a torque that tend to turn the airframe in the roll axis so the aileron of throttle is used to compensate this force.

> Date: Thu, 7 Aug 2014 04:54:28 -0700
> From: address@hidden
> To: address@hidden
> Subject: [Paparazzi-devel] puzzles on the control loops of fixedwing
> Hi,friends!
> Sorry if this isn't a right place for my questions, but I really hope to
> get some useful advice here. I need to understand the whole flight
> mechanism of fixedwing aircrafts,including the flight plan level,the control
> level and the interface between hardwares(gps module,etc).This is a pretty
> difficult task given by my teacher and I have to do my best.I am not looking
> for a complete and exact answer(it does not even exist),though.Instead,any
> general ideas that give me directions and help my understanding are
> appreciated.
> The “control loops” documentation page is very useful for understanding
> the control part of the fixedwings.However,it actually is showing what and
> how,rather why.To get a clear understanding of it,knowing the meaning of the
> relative variables is vital.To do so,it is really a big headache,though
> sourceinsight reduced much work.I have to get sank in the code and try to
> deduce their meaning.
> The following are my puzzles.All my discsusion is about fixedwing in AUTO
> Throttle Climb Mode(no AGR_CLIMB,without airspeed sensor,no energy control)
> ,ie the most 'simple and classic' case of fixedwing.the code is v5.05 stable
> version.
> The first puzzle is the 'h_ctl_aileron_of_throttle' variable,seen in the
> Roll loop.It multifys another variable 'h_ctl_throttle_setpoint' and add to
> the 'h_ctl_roll_setpoint' err.So why the throttle has an inpact on the roll
> channel? and why they have different signs?
> The second is the 'v_ctl_altitude_pre_climb' variable,seen in the
> Altitude loop.What's the meaning
> of it?and how does it come out?
> Third,in Pitch loop,what does 'loiter()' mean?What's the relationship
> between 'nav_pitch','v_ctl_pitch_of_vz' and 'h_ctl_pitch_setpoint'? what's
> the meaning of each one?Why 'estimator_phi' is involved in this
> loop(similar with 'h_ctl_throttle_setpoint' in the Roll loop)?
> Fourth,and the 'real' puzzle,it seems that the implementation of the
> control loop in the code doesn't conform with the diagram,for example,as the
> diagram shows in the Pitch loop,the input of the Bound block is made by
> loiter PLUS the 'PD*theta_err' ,but in the code,there is:
> *float cmd = -h_ctl_pitch_pgain * (err + h_ctl_pitch_dgain * d_err);*
> So why is '-'used?Aren't all the *_pgain and *_dgains positive? I am not
> sure here, in strong hope that someone help me figure it out.
> Beside,I know little about the flight plan level(since we don't have
> that documentation page) and how it interact with the control level(maybe
> through some 'key' variables),but it should be important.any information
> about this is appreciated.
> Thanks for your kindness!
> --
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