ardupilot/libraries/APM_Control/AP_YawController.cpp

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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
// Code by Jon Challinger
//
// This library is free software; you can redistribute it and / or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
#include <AP_Math.h>
#include <AP_HAL.h>
#include "AP_YawController.h"
extern const AP_HAL::HAL& hal;
const AP_Param::GroupInfo AP_YawController::var_info[] PROGMEM = {
AP_GROUPINFO("P", 0, AP_YawController, _kp, 0),
AP_GROUPINFO("I", 1, AP_YawController, _ki, 0),
AP_GROUPINFO("IMAX", 2, AP_YawController, _imax, 0),
AP_GROUPEND
};
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// Low pass filter cut frequency for derivative calculation.
// FCUT macro computes a frequency cut based on an acceptable delay.
#define FCUT(d) (1 / ( 2 * 3.14f * (d) ) )
const float AP_YawController::_fCut = FCUT(0.5f);
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int32_t AP_YawController::get_servo_out(float scaler, bool stick_movement)
{
uint32_t tnow = hal.scheduler->millis();
uint32_t dt = tnow - _last_t;
if (_last_t == 0 || dt > 1000) {
dt = 0;
}
_last_t = tnow;
if(_ins == NULL) { // can't control without a reference
return 0;
}
float delta_time = (float) dt / 1000.0f;
if(stick_movement) {
if(!_stick_movement) {
_stick_movement_begin = tnow;
} else {
if(_stick_movement_begin < tnow-333) {
_freeze_start_time = tnow;
}
}
}
_stick_movement = stick_movement;
Vector3f accels = _ins->get_accel();
// I didn't pull 512 out of a hat - it is a (very) loose approximation of
// 100*ToDeg(asinf(-accels.y/9.81f))
// which, with a P of 1.0, would mean that your rudder angle would be
// equal to your roll angle when
// the plane is still. Thus we have an (approximate) unit to go by.
float error = 512 * -accels.y;
// strongly filter the error
float RC = 1/(2*PI*_fCut);
error = _last_error +
(delta_time / (RC + delta_time)) * (error - _last_error);
_last_error = error;
// integrator
if(_freeze_start_time < (tnow - 2000)) {
if ((fabsf(_ki) > 0) && (dt > 0)) {
_integrator += (error * _ki) * scaler * delta_time;
if (_integrator < -_imax) _integrator = -_imax;
else if (_integrator > _imax) _integrator = _imax;
}
} else {
_integrator = 0;
}
return (error * _kp * scaler) + _integrator;
}
void AP_YawController::reset_I()
{
_integrator = 0;
}