src/Instrumentation/attitude_indicator.cxx

   1 // attitude_indicator.cxx - a vacuum-powered attitude indicator.
   2 // Written by David Megginson, started 2002.
   3 //
   4 // This file is in the Public Domain and comes with no warranty.
   5
   6 // TODO:
   7 // - better spin-up
   8
   9 #include <math.h>       // fabs()
  10
  11 #include "attitude_indicator.hxx"
  12 #include <Main/fg_props.hxx>
  13 #include <Main/util.hxx>
  14
  15
  16 AttitudeIndicator::AttitudeIndicator ()
  17 {
  18 }
  19
  20 AttitudeIndicator::~AttitudeIndicator ()
  21 {
  22 }
  23
  24 void
  25 AttitudeIndicator::init ()
  26 {
  27                                 // TODO: allow index of pump and AI
  28                                 // to be configured.
  29     _pitch_in_node = fgGetNode("/orientation/pitch-deg", true);
  30     _roll_in_node = fgGetNode("/orientation/roll-deg", true);
  31     _suction_node = fgGetNode("/systems/vacuum[0]/suction-inhg", true);
  32     _tumble_flag_node =
  33         fgGetNode("/instrumentation/attitude-indicator/config/tumble-flag",
  34                   true);
  35     _caged_node =
  36         fgGetNode("/instrumentation/attitude-indicator/caged-flag", true);
  37     _tumble_node =
  38         fgGetNode("/instrumentation/attitude-indicator/tumble-norm", true);
  39     _pitch_out_node =
  40         fgGetNode("/instrumentation/attitude-indicator/indicated-pitch-deg",
  41                   true);
  42     _roll_out_node =
  43         fgGetNode("/instrumentation/attitude-indicator/indicated-roll-deg",
  44                   true);
  45 }
  46
  47 void
  48 AttitudeIndicator::bind ()
  49 {
  50     fgTie("/instrumentation/attitude-indicator/serviceable",
  51           &_gyro, &Gyro::is_serviceable, &Gyro::set_serviceable);
  52     fgTie("/instrumentation/attitude-indicator/spin",
  53           &_gyro, &Gyro::get_spin_norm, &Gyro::set_spin_norm);
  54 }
  55
  56 void
  57 AttitudeIndicator::unbind ()
  58 {
  59     fgUntie("/instrumentation/attitude-indicator/serviceable");
  60     fgUntie("/instrumentation/attitude-indicator/spin");
  61 }
  62
  63 void
  64 AttitudeIndicator::update (double dt)
  65 {
  66                                 // If it's caged, it doesn't indicate
  67     if (_caged_node->getBoolValue()) {
  68         _roll_out_node->setDoubleValue(0.0);
  69         _pitch_out_node->setDoubleValue(0.0);
  70         return;
  71     }
  72
  73                                 // Get the spin from the gyro
  74     _gyro.set_power_norm(_suction_node->getDoubleValue()/5.0);
  75     _gyro.update(dt);
  76     double spin = _gyro.get_spin_norm();
  77
  78                                 // Calculate the responsiveness
  79     double responsiveness = spin * spin * spin * spin * spin * spin;
  80
  81                                 // Get the indicated roll and pitch
  82     double roll = _roll_in_node->getDoubleValue();
  83     double pitch = _pitch_in_node->getDoubleValue();
  84
  85                                 // Calculate the tumble for the
  86                                 // next pass.
  87     if (_tumble_flag_node->getBoolValue()) {
  88         double tumble = _tumble_node->getDoubleValue();
  89         if (fabs(roll) > 45.0) {
  90             double target = (fabs(roll) - 45.0) / 45.0;
  91             target *= target;   // exponential past +-45 degrees
  92             if (roll < 0)
  93                 target = -target;
  94
  95             if (fabs(target) > fabs(tumble))
  96                 tumble = target;
  97
  98             if (tumble > 1.0)
  99                 tumble = 1.0;
 100             else if (tumble < -1.0)
 101                 tumble = -1.0;
 102         }
 103                                     // Reerect in 5 minutes
 104         double step = dt/300.0;
 105         if (tumble < -step)
 106             tumble += step;
 107         else if (tumble > step)
 108             tumble -= step;
 109
 110         roll += tumble * 45;
 111         _tumble_node->setDoubleValue(tumble);
 112     }
 113
 114     roll = fgGetLowPass(_roll_out_node->getDoubleValue(), roll,
 115                         responsiveness);
 116     pitch = fgGetLowPass(_pitch_out_node->getDoubleValue(), pitch,
 117                          responsiveness);
 118
 119                                 // Assign the new values
 120     _roll_out_node->setDoubleValue(roll);
 121     _pitch_out_node->setDoubleValue(pitch);
 122 }
 123
 124 // end of attitude_indicator.cxx