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[Paparazzi-devel] Question about the Steps response of pitch

From: Haiyang Chao
Subject: [Paparazzi-devel] Question about the Steps response of pitch
Date: Thu, 4 Dec 2008 09:28:32 -0700

Hi, all.

I am trying to do a step response analysis to see if I can get a model from the elevator--pitch loop. But I found out that the simulation of step response of pitch can never track the desired square wave (see the attachment). I checked the control code and I think this is due to the fact that the desired altitude is also set, so the input of the pitch step response is actually three: pitch(square wave +-10), roll(0), altitude (250).

So my question is that why the desired altitude is also set in the pitch response. I know this will be good for the flight stability. But I still think more information of step response is missing.

BTW: there are quite some control variables defined and I can not find clear explanations on the wiki. Like v_ctl_climb_mode, lateral_mode, v_ctl_mode. Could somebody explain these to me?

I used mj5 airframe and versatile.xml for flight plan. The syntax is like this:
       <attitude alt="250" roll="20.0" until=" stage_time > 3" vmode="alt"/>
        <attitude alt="250" roll="-20.0" until="stage_time > 3" vmode="alt"/>
I traced back to flight_plan.h. So the real control command is :
/* lateral_mode = LATERAL_MODE_ROLL, h_ctl_roll_setpoint = _roll*/
/*v_ctl_climb_mode = V_CTL_CLIMB_MODE_AUTO_THROTTLE, nav_pitch = _pitch*/
            NavVerticalAltitudeMode(250, 0.);
/*v_ctrl_mode = V_CTL_MODE_AUTO_ALT, nav_altitude = -alt, v_ctl_altitude_pre_climb = _preclimb*/


Attachment: pitch_step_response.png
Description: PNG image

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