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 1.6  1998/10/17 01:34:16  curt
  40 C++ ifying ...
  41
  42 Revision 1.5  1998/09/29 02:03:00  curt
  43 Added a brake + autopilot mods.
  44
  45 Revision 1.4  1998/08/06 12:46:40  curt
  46 Header change.
  47
  48 Revision 1.3  1998/02/03 23:20:18  curt
  49 Lots of little tweaks to fix various consistency problems discovered by
  50 Solaris' CC.  Fixed a bug in fg_debug.c with how the fgPrintf() wrapper
  51 passed arguments along to the real printf().  Also incorporated HUD changes
  52 by Michele America.
  53
  54 Revision 1.2  1998/01/19 18:40:29  curt
  55 Tons of little changes to clean up the code and to remove fatal errors
  56 when building with the c++ compiler.
  57
  58 Revision 1.1  1997/05/29 00:10:02  curt
  59 Initial Flight Gear revision.
  60
  61
  62 ----------------------------------------------------------------------------
  63
  64         REFERENCES:
  65
  66 ----------------------------------------------------------------------------
  67
  68         CALLED BY:
  69
  70 ----------------------------------------------------------------------------
  71
  72         CALLS TO:
  73
  74 ----------------------------------------------------------------------------
  75
  76         INPUTS:
  77
  78 ----------------------------------------------------------------------------
  79
  80         OUTPUTS:
  81
  82 --------------------------------------------------------------------------*/
  83 #include <math.h>
  84 #include "ls_types.h"
  85 #include "ls_constants.h"
  86 #include "ls_generic.h"
  87 #include "ls_cockpit.h"
  88
  89
  90 void sub3( DATA v1[],  DATA v2[], DATA result[] )
  91 {
  92     result[0] = v1[0] - v2[0];
  93     result[1] = v1[1] - v2[1];
  94     result[2] = v1[2] - v2[2];
  95 }
  96
  97 void add3( DATA v1[],  DATA v2[], DATA result[] )
  98 {
  99     result[0] = v1[0] + v2[0];
 100     result[1] = v1[1] + v2[1];
 101     result[2] = v1[2] + v2[2];
 102 }
 103
 104 void cross3( DATA v1[],  DATA v2[], DATA result[] )
 105 {
 106     result[0] = v1[1]*v2[2] - v1[2]*v2[1];
 107     result[1] = v1[2]*v2[0] - v1[0]*v2[2];
 108     result[2] = v1[0]*v2[1] - v1[1]*v2[0];
 109 }
 110
 111 void multtrans3x3by3( DATA m[][3], DATA v[], DATA result[] )
 112 {
 113     result[0] = m[0][0]*v[0] + m[1][0]*v[1] + m[2][0]*v[2];
 114     result[1] = m[0][1]*v[0] + m[1][1]*v[1] + m[2][1]*v[2];
 115     result[2] = m[0][2]*v[0] + m[1][2]*v[1] + m[2][2]*v[2];
 116 }
 117
 118 void mult3x3by3( DATA m[][3], DATA v[], DATA result[] )
 119 {
 120     result[0] = m[0][0]*v[0] + m[0][1]*v[1] + m[0][2]*v[2];
 121     result[1] = m[1][0]*v[0] + m[1][1]*v[1] + m[1][2]*v[2];
 122     result[2] = m[2][0]*v[0] + m[2][1]*v[1] + m[2][2]*v[2];
 123 }
 124
 125 void clear3( DATA v[] )
 126 {
 127     v[0] = 0.; v[1] = 0.; v[2] = 0.;
 128 }
 129
 130 void gear( SCALAR dt, int Initialize ) {
 131 char rcsid[] = "$Id$";
 132
 133   /*
 134    * Aircraft specific initializations and data goes here
 135    */
 136
 137 #define NUM_WHEELS 3
 138
 139     static int num_wheels = NUM_WHEELS;             /* number of wheels  */
 140     static DATA d_wheel_rp_body_v[NUM_WHEELS][3] =  /* X, Y, Z locations */
 141     {
 142         { 10.,  0., 4. },                               /* in feet */
 143         { -1.,  3., 4. },
 144         { -1., -3., 4. }
 145     };
 146     static DATA spring_constant[NUM_WHEELS] =       /* springiness, lbs/ft */
 147         { 1500., 5000., 5000. };
 148     static DATA spring_damping[NUM_WHEELS] =        /* damping, lbs/ft/sec */
 149         { 100.,  150.,  150. };
 150     static DATA percent_brake[NUM_WHEELS] =         /* percent applied braking */
 151         { 0.,  0.,  0. };                           /* 0 = none, 1 = full */
 152     static DATA caster_angle_rad[NUM_WHEELS] =      /* steerable tires - in */
 153         { 0., 0., 0.};                              /* radians, +CW */
 154   /*
 155    * End of aircraft specific code
 156    */
 157
 158   /*
 159    * Constants & coefficients for tyres on tarmac - ref [1]
 160    */
 161
 162     /* skid function looks like:
 163      *
 164      *           mu  ^
 165      *               |
 166      *       max_mu  |       +
 167      *               |      /|
 168      *   sliding_mu  |     / +------
 169      *               |    /
 170      *               |   /
 171      *               +--+------------------------>
 172      *               |  |    |      sideward V
 173      *               0 bkout skid
 174      *                 V     V
 175      */
 176
 177
 178     static DATA sliding_mu   = 0.5;
 179     static DATA rolling_mu   = 0.01;
 180     static DATA max_brake_mu = 0.6;
 181     static DATA max_mu       = 0.8;
 182     static DATA bkout_v      = 0.1;
 183     static DATA skid_v       = 1.0;
 184   /*
 185    * Local data variables
 186    */
 187
 188     DATA d_wheel_cg_body_v[3];          /* wheel offset from cg,  X-Y-Z */
 189     DATA d_wheel_cg_local_v[3];         /* wheel offset from cg,  N-E-D */
 190     DATA d_wheel_rwy_local_v[3];        /* wheel offset from rwy, N-E-U */
 191     DATA v_wheel_body_v[3];             /* wheel velocity,        X-Y-Z */
 192     DATA v_wheel_local_v[3];            /* wheel velocity,        N-E-D */
 193     DATA f_wheel_local_v[3];            /* wheel reaction force,  N-E-D */
 194     DATA temp3a[3], temp3b[3], tempF[3], tempM[3];
 195     DATA reaction_normal_force;         /* wheel normal (to rwy) force  */
 196     DATA cos_wheel_hdg_angle, sin_wheel_hdg_angle;      /* temp storage */
 197     DATA v_wheel_forward, v_wheel_sideward,  abs_v_wheel_sideward;
 198     DATA forward_mu, sideward_mu;       /* friction coefficients        */
 199     DATA beta_mu;                       /* breakout friction slope      */
 200     DATA forward_wheel_force, sideward_wheel_force;
 201
 202     int i;                              /* per wheel loop counter */
 203
 204   /*
 205    * Execution starts here
 206    */
 207
 208     beta_mu = max_mu/(skid_v-bkout_v);
 209     clear3( F_gear_v );         /* Initialize sum of forces...  */
 210     clear3( M_gear_v );         /* ...and moments               */
 211
 212   /*
 213    * Put aircraft specific executable code here
 214    */
 215
 216     /* replace with cockpit brake handle connection code */
 217     percent_brake[1] = Brake_pct;
 218     percent_brake[2] = percent_brake[1];
 219
 220     caster_angle_rad[0] = 0.03*Rudder_pedal;
 221
 222     for (i=0;i<num_wheels;i++)      /* Loop for each wheel */
 223     {
 224         /*========================================*/
 225         /* Calculate wheel position w.r.t. runway */
 226         /*========================================*/
 227
 228             /* First calculate wheel location w.r.t. cg in body (X-Y-Z) axes... */
 229
 230         sub3( d_wheel_rp_body_v[i], D_cg_rp_body_v, d_wheel_cg_body_v );
 231
 232             /* then converting to local (North-East-Down) axes... */
 233
 234         multtrans3x3by3( T_local_to_body_m,  d_wheel_cg_body_v, d_wheel_cg_local_v );
 235
 236             /* Runway axes correction - third element is Altitude, not (-)Z... */
 237
 238         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* since altitude = -Z */
 239
 240             /* Add wheel offset to cg location in local axes */
 241
 242         add3( d_wheel_cg_local_v, D_cg_rwy_local_v, d_wheel_rwy_local_v );
 243
 244             /* remove Runway axes correction so right hand rule applies */
 245
 246         d_wheel_cg_local_v[2] = -d_wheel_cg_local_v[2]; /* now Z positive down */
 247
 248         /*============================*/
 249         /* Calculate wheel velocities */
 250         /*============================*/
 251
 252             /* contribution due to angular rates */
 253
 254         cross3( Omega_body_v, d_wheel_cg_body_v, temp3a );
 255
 256             /* transform into local axes */
 257
 258         multtrans3x3by3( T_local_to_body_m, temp3a, temp3b );
 259
 260             /* plus contribution due to cg velocities */
 261
 262         add3( temp3b, V_local_rel_ground_v, v_wheel_local_v );
 263
 264
 265         /*===========================================*/
 266         /* Calculate forces & moments for this wheel */
 267         /*===========================================*/
 268
 269             /* Add any anticipation, or frame lead/prediction, here... */
 270
 271                     /* no lead used at present */
 272
 273             /* Calculate sideward and forward velocities of the wheel
 274                     in the runway plane                                 */
 275
 276         cos_wheel_hdg_angle = cos(caster_angle_rad[i] + Psi);
 277         sin_wheel_hdg_angle = sin(caster_angle_rad[i] + Psi);
 278
 279         v_wheel_forward  = v_wheel_local_v[0]*cos_wheel_hdg_angle
 280                          + v_wheel_local_v[1]*sin_wheel_hdg_angle;
 281         v_wheel_sideward = v_wheel_local_v[1]*cos_wheel_hdg_angle
 282                          - v_wheel_local_v[0]*sin_wheel_hdg_angle;
 283
 284             /* Calculate normal load force (simple spring constant) */
 285
 286         reaction_normal_force = 0.;
 287         if( d_wheel_rwy_local_v[2] < 0. )
 288         {
 289             reaction_normal_force = spring_constant[i]*d_wheel_rwy_local_v[2]
 290                                   - v_wheel_local_v[2]*spring_damping[i];
 291             if (reaction_normal_force > 0.) reaction_normal_force = 0.;
 292                 /* to prevent damping component from swamping spring component */
 293         }
 294
 295             /* Calculate friction coefficients */
 296
 297         forward_mu = (max_brake_mu - rolling_mu)*percent_brake[i] + rolling_mu;
 298         abs_v_wheel_sideward = sqrt(v_wheel_sideward*v_wheel_sideward);
 299         sideward_mu = sliding_mu;
 300         if (abs_v_wheel_sideward < skid_v)
 301             sideward_mu = (abs_v_wheel_sideward - bkout_v)*beta_mu;
 302         if (abs_v_wheel_sideward < bkout_v) sideward_mu = 0.;
 303
 304             /* Calculate foreward and sideward reaction forces */
 305
 306         forward_wheel_force  =   forward_mu*reaction_normal_force;
 307         sideward_wheel_force =  sideward_mu*reaction_normal_force;
 308         if(v_wheel_forward < 0.) forward_wheel_force = -forward_wheel_force;
 309         if(v_wheel_sideward < 0.) sideward_wheel_force = -sideward_wheel_force;
 310
 311             /* Rotate into local (N-E-D) axes */
 312
 313         f_wheel_local_v[0] = forward_wheel_force*cos_wheel_hdg_angle
 314                           - sideward_wheel_force*sin_wheel_hdg_angle;
 315         f_wheel_local_v[1] = forward_wheel_force*sin_wheel_hdg_angle
 316                           + sideward_wheel_force*cos_wheel_hdg_angle;
 317         f_wheel_local_v[2] = reaction_normal_force;
 318
 319             /* Convert reaction force from local (N-E-D) axes to body (X-Y-Z) */
 320
 321         mult3x3by3( T_local_to_body_m, f_wheel_local_v, tempF );
 322
 323             /* Calculate moments from force and offsets in body axes */
 324
 325         cross3( d_wheel_cg_body_v, tempF, tempM );
 326
 327         /* Sum forces and moments across all wheels */
 328
 329         add3( tempF, F_gear_v, F_gear_v );
 330         add3( tempM, M_gear_v, M_gear_v );
 331
 332     }
 333 }