LaRCsim/navion_gear.c

   1 /***************************************************************************
   2
   3         TITLE:  gear
   4
   5 ----------------------------------------------------------------------------
   6
   7         FUNCTION:       Landing gear model for example simulation
   8
   9 ----------------------------------------------------------------------------
  10
  11         MODULE STATUS:  developmental
  12
  13 ----------------------------------------------------------------------------
  14
  15         GENEALOGY:      Created 931012 by E. B. Jackson
  16
  17 ----------------------------------------------------------------------------
  18
  19         DESIGNED BY:    E. B. Jackson
  20
  21         CODED BY:       E. B. Jackson
  22
  23         MAINTAINED BY:  E. B. Jackson
  24
  25 ----------------------------------------------------------------------------
  26
  27         MODIFICATION HISTORY:
  28
  29         DATE    PURPOSE                                         BY
  30
  31         931218  Added navion.h header to allow connection with
  32                 aileron displacement for nosewheel steering.    EBJ
  33         940511  Connected nosewheel to rudder pedal; adjusted gain.
  34
  35         CURRENT RCS HEADER:
  36
  37 $Header$
  38 $Log$
  39 Revision 1.5  1998/09/29 02:03:00  curt
  40 Added a brake + autopilot mods.
  41
  42 Revision 1.4  1998/08/06 12:46:40  curt
  43 Header change.
  44
  45 Revision 1.3  1998/02/03 23:20:18  curt
  46 Lots of little tweaks to fix various consistency problems discovered by
  47 Solaris' CC.  Fixed a bug in fg_debug.c with how the fgPrintf() wrapper
  48 passed arguments along to the real printf().  Also incorporated HUD changes
  49 by Michele America.
  50
  51 Revision 1.2  1998/01/19 18:40:29  curt
  52 Tons of little changes to clean up the code and to remove fatal errors
  53 when building with the c++ compiler.
  54
  55 Revision 1.1  1997/05/29 00:10:02  curt
  56 Initial Flight Gear revision.
  57
  58
  59 ----------------------------------------------------------------------------
  60
  61         REFERENCES:
  62
  63 ----------------------------------------------------------------------------
  64
  65         CALLED BY:
  66
  67 ----------------------------------------------------------------------------
  68
  69         CALLS TO:
  70
  71 ----------------------------------------------------------------------------
  72
  73         INPUTS:
  74
  75 ----------------------------------------------------------------------------
  76
  77         OUTPUTS:
  78
  79 --------------------------------------------------------------------------*/
  80 #include <math.h>
  81 #include "ls_types.h"
  82 #include "ls_constants.h"
  83 #include "ls_generic.h"
  84 #include "ls_cockpit.h"
  85
  86 #include <Controls/controls.h>
  87
  88 void sub3( DATA v1[],  DATA v2[], DATA result[] )
  89 {
  90     result[0] = v1[0] - v2[0];
  91     result[1] = v1[1] - v2[1];
  92     result[2] = v1[2] - v2[2];
  93 }
  94
  95 void add3( DATA v1[],  DATA v2[], DATA result[] )
  96 {
  97     result[0] = v1[0] + v2[0];
  98     result[1] = v1[1] + v2[1];
  99     result[2] = v1[2] + v2[2];
 100 }
 101
 102 void cross3( DATA v1[],  DATA v2[], DATA result[] )
 103 {
 104     result[0] = v1[1]*v2[2] - v1[2]*v2[1];
 105     result[1] = v1[2]*v2[0] - v1[0]*v2[2];
 106     result[2] = v1[0]*v2[1] - v1[1]*v2[0];
 107 }
 108
 109 void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
 110 {
 111     result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
 112     result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
 113     result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
 114 }
 115
 116 void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
 117 {
 118     result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
 119     result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
 120     result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
 121 }
 122
 123 void clear3( DATA v[] )
 124 {
 125     v[0] = 0.; v[1] = 0.; v[2] = 0.;
 126 }
 127
 128 void gear( SCALAR dt, int Initialize ) {
 129 char rcsid[] = "$Id$";
 130
 131   /*
 132    * Aircraft specific initializations and data goes here
 133    */
 134
 135 #define NUM_WHEELS 3
 136
 137     static int num_wheels = NUM_WHEELS;             /* number of wheels  */
 138     static DATA d_wheel_rp_body_v[NUM_WHEELS][3] =  /* X, Y, Z locations */
 139     {
 140         { 10.,  0., 4. },                               /* in feet */
 141         { -1.,  3., 4. },
 142         { -1., -3., 4. }
 143     };
 144     static DATA spring_constant[NUM_WHEELS] =       /* springiness, lbs/ft */
 145         { 1500., 5000., 5000. };
 146     static DATA spring_damping[NUM_WHEELS] =        /* damping, lbs/ft/sec */
 147         { 100.,  150.,  150. };
 148     static DATA percent_brake[NUM_WHEELS] =         /* percent applied braking */
 149         { 0.,  0.,  0. };                           /* 0 = none, 1 = full */
 150     static DATA caster_angle_rad[NUM_WHEELS] =      /* steerable tires - in */
 151         { 0., 0., 0.};                              /* radians, +CW */
 152   /*
 153    * End of aircraft specific code
 154    */
 155
 156   /*
 157    * Constants & coefficients for tyres on tarmac - ref [1]
 158    */
 159
 160     /* skid function looks like:
 161      *
 162      *           mu  ^
 163      *               |
 164      *       max_mu  |       +
 165      *               |      /|
 166      *   sliding_mu  |     / +------
 167      *               |    /
 168      *               |   /
 169      *               +--+------------------------>
 170      *               |  |    |      sideward V
 171      *               0 bkout skid
 172      *                 V     V
 173      */
 174
 175
 176     static DATA sliding_mu   = 0.5;
 177     static DATA rolling_mu   = 0.01;
 178     static DATA max_brake_mu = 0.6;
 179     static DATA max_mu       = 0.8;
 180     static DATA bkout_v      = 0.1;
 181     static DATA skid_v       = 1.0;
 182   /*
 183    * Local data variables
 184    */
 185
 186     DATA d_wheel_cg_body_v[3];          /* wheel offset from cg,  X-Y-Z */
 187     DATA d_wheel_cg_local_v[3];         /* wheel offset from cg,  N-E-D */
 188     DATA d_wheel_rwy_local_v[3];        /* wheel offset from rwy, N-E-U */
 189     DATA v_wheel_body_v[3];             /* wheel velocity,        X-Y-Z */
 190     DATA v_wheel_local_v[3];            /* wheel velocity,        N-E-D */
 191     DATA f_wheel_local_v[3];            /* wheel reaction force,  N-E-D */
 192     DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
 193     DATA reaction_normal_force;         /* wheel normal (to rwy) force  */
 194     DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle;      /* temp storage */
 195     DATA v_wheel_forward, v_wheel_sideward,  abs_v_wheel_sideward;
 196     DATA forward_mu, sideward_mu;       /* friction coefficients        */
 197     DATA beta_mu;                       /* breakout friction slope      */
 198     DATA forward_wheel_force, sideward_wheel_force;
 199
 200     int i;                              /* per wheel loop counter */
 201
 202   /*
 203    * Execution starts here
 204    */
 205
 206     beta_mu = max_mu/(skid_v-bkout_v);
 207     clear3( F_gear_v );         /* Initialize sum of forces...  */
 208     clear3( M_gear_v );         /* ...and moments               */
 209
 210   /*
 211    * Put aircraft specific executable code here
 212    */
 213
 214     percent_brake[1] = fgBrakeGet(); /* replace with cockpit brake handle connection code */
 215     percent_brake[2] = percent_brake[1];
 216
 217     caster_angle_rad[0] = 0.03*Rudder_pedal;
 218
 219     for (i=0;i<num_wheels;i++)      /* Loop for each wheel */
 220     {
 221         /*========================================*/
 222         /* Calculate wheel position w.r.t. runway */
 223         /*========================================*/
 224
 225             /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
 226
 227         sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
 228
 229             /* then converting to local (North-East-Down) axes... */
 230
 231         multtrans3x3by3( T_local_to_body_m,  d_wheel_cg_body_v, d_wheel_cg_local_v );
 232
 233             /* Runway axes correction - third element is Altitude, not (-)Z... */
 234
 235         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
 236
 237             /* Add wheel offset to cg location in local axes */
 238
 239         add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
 240
 241             /* remove Runway axes correction so right hand rule applies */
 242
 243         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
 244
 245         /*============================*/
 246         /* Calculate wheel velocities */
 247         /*============================*/
 248
 249             /* contribution due to angular rates */
 250
 251         cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
 252
 253             /* transform into local axes */
 254
 255         multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
 256
 257             /* plus contribution due to cg velocities */
 258
 259         add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
 260
 261
 262         /*===========================================*/
 263         /* Calculate forces & moments for this wheel */
 264         /*===========================================*/
 265
 266             /* Add any anticipation, or frame lead/prediction, here... */
 267
 268                     /* no lead used at present */
 269
 270             /* Calculate sideward and forward velocities of the wheel
 271                     in the runway plane                                 */
 272
 273         cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
 274         sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
 275
 276         v_wheel_forward  = v_wheel_local_v[0]*cos_wheel_hdg_angle
 277                          + v_wheel_local_v[1]*sin_wheel_hdg_angle;
 278         v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
 279                          - v_wheel_local_v[0]*sin_wheel_hdg_angle;
 280
 281             /* Calculate normal load force (simple spring constant) */
 282
 283         reaction_normal_force = 0.;
 284         if( d_wheel_rwy_local_v[2] < 0. )
 285         {
 286             reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
 287                                   - v_wheel_local_v[2]*spring_damping[i];
 288             if (reaction_normal_force > 0.) reaction_normal_force = 0.;
 289                 /* to prevent damping component from swamping spring component */
 290         }
 291
 292             /* Calculate friction coefficients */
 293
 294         forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
 295         abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
 296         sideward_mu = sliding_mu;
 297         if (abs_v_wheel_sideward < skid_v)
 298             sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
 299         if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
 300
 301             /* Calculate foreward and sideward reaction forces */
 302
 303         forward_wheel_force  =   forward_mu*reaction_normal_force;
 304         sideward_wheel_force =  sideward_mu*reaction_normal_force;
 305         if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
 306         if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
 307
 308             /* Rotate into local (N-E-D) axes */
 309
 310         f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
 311                           - sideward_wheel_force*sin_wheel_hdg_angle;
 312         f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
 313                           + sideward_wheel_force*cos_wheel_hdg_angle;
 314         f_wheel_local_v[2] = reaction_normal_force;
 315
 316             /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
 317
 318         mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
 319
 320             /* Calculate moments from force and offsets in body axes */
 321
 322         cross3( d_wheel_cg_body_v, tempF, tempM );
 323
 324         /* Sum forces and moments across all wheels */
 325
 326         add3( tempF, F_gear_v, F_gear_v );
 327         add3( tempM, M_gear_v, M_gear_v );
 328
 329     }
 330 }