flightgear/src/Instrumentation/mrg.cxx

// MRG.cxx - an electrically powered master reference gyro.
// Written by Vivian Meazza based on work by David Megginson, started 2006.
//
// This file is in the Public Domain and comes with no warranty.

// TODO:
// - better spin-up

#include <simgear/compiler.h>

#include <iostream>
#include <string>
#include <sstream>
#include <math.h>	// fabs()

#include <Main/fg_props.hxx>
#include <Main/util.hxx>

#include "mrg.hxx"


MasterReferenceGyro::MasterReferenceGyro ( SGPropertyNode *node ) :
	_name(node->getStringValue("name", "master-reference-gyro")),
	_num(node->getIntValue("number", 0))
{
}

MasterReferenceGyro::~MasterReferenceGyro ()
{
}

void
MasterReferenceGyro::init ()
{
	_last_hdg = 0;
	_last_roll = 0;
	_last_pitch = 0;
	_indicated_hdg = 0;
	_indicated_roll = 0;
	_indicated_pitch = 0;
	_indicated_hdg_rate = 0;
	_indicated_roll_rate = 0;
	_indicated_pitch_rate = 0;
	
	string branch;
	branch = "/instrumentation/" + _name;

	_pitch_in_node = fgGetNode("/orientation/pitch-deg", true);
	_roll_in_node = fgGetNode("/orientation/roll-deg", true);
	_hdg_in_node = fgGetNode("/orientation/heading-deg", true);
	_pitch_rate_node = fgGetNode("/orientation/pitch-rate-degps", true);
	_roll_rate_node = fgGetNode("/orientation/roll-rate-degps", true);
	_yaw_rate_node = fgGetNode("/orientation/yaw-rate-degps", true);
	_g_in_node =   fgGetNode("/accelerations/pilot-g-damped", true);
	_electrical_node = fgGetNode("/systems/electrical/outputs/MRG", true);
	
	SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
	_off_node = node->getChild("off-flag", 0, true);
	_pitch_out_node = node->getChild("indicated-pitch-deg", 0, true);
	_roll_out_node = node->getChild("indicated-roll-deg", 0, true);
	_hdg_out_node = node->getChild("indicated-hdg-deg", 0, true);
	_pitch_rate_out_node = node->getChild("indicated-pitch-rate-degps", 0, true);
	_roll_rate_out_node = node->getChild("indicated-roll-rate-degps", 0, true);
	_hdg_rate_out_node = node->getChild("indicated-hdg-rate-degps", 0, true);
	_responsiveness_node = node->getChild("responsiveness", 0, true);
	_error_out_node = node->getChild("heading-error-deg", 0, true);

	_electrical_node->setDoubleValue(0);
	_responsiveness_node->setDoubleValue(0.75);
	_off_node->setBoolValue(false);
}

void
MasterReferenceGyro::bind ()
{
	std::ostringstream temp;
	string branch;
	temp << _num;
	branch = "/instrumentation/" + _name + "[" + temp.str() + "]";

	fgTie((branch + "/serviceable").c_str(),
		&_gyro, &Gyro::is_serviceable, &Gyro::set_serviceable);
	fgTie((branch + "/spin").c_str(),
		&_gyro, &Gyro::get_spin_norm, &Gyro::set_spin_norm);
}

void
MasterReferenceGyro::unbind ()
{
	std::ostringstream temp;
	string branch;
	temp << _num;
	branch = "/instrumentation/" + _name + "[" + temp.str() + "]";

	fgUntie((branch + "/serviceable").c_str());
	fgUntie((branch + "/spin").c_str());
}

void
MasterReferenceGyro::update (double dt)
{
	double indicated_roll = 0;
	double indicated_pitch = 0;
	double indicated_hdg = 0;
	double indicated_roll_rate = 0;
	double indicated_pitch_rate = 0;
	double indicated_hdg_rate = 0;

	// Get the spin from the gyro
	_gyro.set_power_norm( _electrical_node->getDoubleValue()/24 );
	_gyro.update(dt);
	double spin = _gyro.get_spin_norm();
	
	// set the "off-flag"
	if ( _electrical_node->getDoubleValue() == 0 ) {
		_off_node->setBoolValue(true);
	} else if ( spin == 1 ) {
		_off_node->setBoolValue(false);
	} else {
		_off_node->setBoolValue(true);
	}

	// Get the input values
	double roll = _roll_in_node->getDoubleValue();
	double pitch = _pitch_in_node->getDoubleValue();
	double hdg = _hdg_in_node->getDoubleValue();
	double roll_rate = _yaw_rate_node->getDoubleValue();
	double pitch_rate = _yaw_rate_node->getDoubleValue();
	double yaw_rate = _yaw_rate_node->getDoubleValue();

	//modulate the input by the spin rate
	double responsiveness = spin * spin * spin * spin * spin * spin;
	roll = fgGetLowPass( _last_roll, roll, responsiveness );
	pitch = fgGetLowPass( _last_pitch , pitch, responsiveness );
	hdg = fgGetLowPass( _last_hdg , hdg, responsiveness );

	//but we need to filter the hdg and yaw_rate as well - yuk!
	responsiveness = 0.1 / (spin * spin * spin * spin * spin * spin);
	yaw_rate = fgGetLowPass( _last_yaw_rate , yaw_rate, responsiveness );

	// store the new values
	_last_roll = roll;
	_last_pitch = pitch;
	_last_hdg = hdg;
	_last_roll_rate = roll_rate;
	_last_pitch_rate = pitch_rate;
	_last_yaw_rate = yaw_rate;

	//the gyro only erects inside limits
	if ( fabs ( yaw_rate ) <= 5
			&& (_g_in_node->getDoubleValue() <= 1.5
			|| _g_in_node->getDoubleValue() >= -0.5) ) {
		indicated_roll = _last_roll;
		indicated_pitch = _last_pitch;
		indicated_hdg = _last_hdg;
		indicated_roll_rate = _last_roll_rate;
		indicated_pitch_rate = _last_pitch_rate;
		indicated_hdg_rate = _last_yaw_rate;
	} else {
		indicated_roll_rate = 0;
		indicated_pitch_rate = 0;
		indicated_hdg_rate = 0;
	}

	// calculate the difference between the indicated heading
	// and the selected heading for use with an autopilot
	static SGPropertyNode *bnode
		= fgGetNode( "autopilot/settings/target-heading-deg", false );

	if ( bnode ) {
		double diff = bnode->getDoubleValue() - indicated_hdg;
		if ( diff < -180.0 ) { diff += 360.0; }
		if ( diff > 180.0 ) { diff -= 360.0; }
		_error_out_node->setDoubleValue( diff );
	}
	//cout << "autopilot input " << bnode->getDoubleValue() << "output " << _error_out_node->getDoubleValue()<<endl ;
	//smooth the output
	double factor = _responsiveness_node->getDoubleValue() * dt;

	indicated_roll = fgGetLowPass( _indicated_roll, indicated_roll, factor );
	indicated_pitch = fgGetLowPass( _indicated_pitch , indicated_pitch, factor );
	indicated_hdg = fgGetLowPass( _indicated_hdg , indicated_hdg, factor );

	indicated_roll_rate = fgGetLowPass( _indicated_roll_rate, indicated_roll_rate, factor );
	indicated_pitch_rate = fgGetLowPass( _indicated_pitch_rate , indicated_pitch_rate, factor );
	indicated_hdg_rate = fgGetLowPass( _indicated_hdg_rate , indicated_hdg_rate, factor );

	// store the new values
	_indicated_roll = indicated_roll;
	_indicated_pitch = indicated_pitch;
	_indicated_hdg = indicated_hdg;

	_indicated_roll_rate = indicated_roll_rate;
	_indicated_pitch_rate = indicated_pitch_rate;
	_indicated_hdg_rate = indicated_hdg_rate;

	// add in a gyro underspin "error" if gyro is spinning too slowly
	const double spin_thresh = 0.8;
	const double max_roll_error = 40.0;
	const double max_pitch_error = 12.0;
	const double max_hdg_error = 140.0;
	double roll_error;
	double pitch_error;
	double hdg_error;

	if ( spin <= spin_thresh ) {
		double roll_error_factor	= ( spin_thresh - spin ) / spin_thresh;
		double pitch_error_factor	= ( spin_thresh - spin ) / spin_thresh;
		double hdg_error_factor		= ( spin_thresh - spin ) / spin_thresh;
		roll_error	= roll_error_factor * roll_error_factor * max_roll_error;
		pitch_error = pitch_error_factor * pitch_error_factor * max_pitch_error;
		hdg_error	= hdg_error_factor * hdg_error_factor * max_hdg_error;
	} else {
		roll_error = 0.0;
		pitch_error = 0.0;
		hdg_error = 0.0;
	}

	_roll_out_node->setDoubleValue( _indicated_roll + roll_error );
	_pitch_out_node->setDoubleValue( _indicated_pitch + pitch_error );
	_hdg_out_node->setDoubleValue( _indicated_hdg + hdg_error );
	_pitch_rate_out_node ->setDoubleValue( _indicated_pitch_rate );
	_roll_rate_out_node ->setDoubleValue( _indicated_roll_rate );
	_hdg_rate_out_node ->setDoubleValue( _indicated_hdg_rate );
}

// end of mrg.cxx