2 #include "BodyEnvironment.hpp"
3 #include "RigidBody.hpp"
5 #include <simgear/scene/material/mat.hxx>
6 #include <FDM/flight.hxx>
9 static const float YASIM_PI = 3.14159265358979323846;
10 static const float maxGroundBumpAmplitude=0.4;
11 //Amplitude can be positive and negative
17 _pos[i] = _cmpr[i] = 0;
28 _ground_frictionFactor = 1;
29 _ground_rollingFriction = 0.02;
30 _ground_loadCapacity = 1e30;
31 _ground_loadResistance = 1e30;
33 _ground_bumpiness = 0;
38 _reduceFrictionByExtension = 0;
39 _spring_factor_not_planing = 1;
42 _ignoreWhileSolving = 0;
45 _global_ground[i] = _global_vel[i] = 0;
46 _global_ground[2] = 1;
47 _global_ground[3] = -1e3;
50 void Gear::setPosition(float* position)
53 for(i=0; i<3; i++) _pos[i] = position[i];
56 void Gear::setCompression(float* compression)
59 for(i=0; i<3; i++) _cmpr[i] = compression[i];
62 void Gear::setSpring(float spring)
67 void Gear::setDamping(float damping)
72 void Gear::setStaticFriction(float sfric)
77 void Gear::setDynamicFriction(float dfric)
82 void Gear::setBrake(float brake)
84 _brake = Math::clamp(brake, 0, 1);
87 void Gear::setRotation(float rotation)
92 void Gear::setExtension(float extension)
94 _extension = Math::clamp(extension, 0, 1);
97 void Gear::setCastering(bool c)
102 void Gear::setContactPoint(bool c)
107 void Gear::setOnWater(bool c)
112 void Gear::setOnSolid(bool c)
117 void Gear::setIgnoreWhileSolving(bool c)
119 _ignoreWhileSolving = c;
122 void Gear::setSpringFactorNotPlaning(float f)
124 _spring_factor_not_planing = f;
127 void Gear::setSpeedPlaning(float s)
132 void Gear::setReduceFrictionByExtension(float s)
134 _reduceFrictionByExtension = s;
137 void Gear::setInitialLoad(float l)
142 void Gear::setGlobalGround(double *global_ground, float* global_vel,
143 double globalX, double globalY,
144 const SGMaterial *material)
147 double frictionFactor,rollingFriction,loadCapacity,loadResistance,bumpiness;
150 for(i=0; i<4; i++) _global_ground[i] = global_ground[i];
151 for(i=0; i<3; i++) _global_vel[i] = global_vel[i];
154 loadCapacity = (*material).get_load_resistance();
155 frictionFactor =(*material).get_friction_factor();
156 rollingFriction = (*material).get_rolling_friction();
157 loadResistance = (*material).get_load_resistance();
158 bumpiness = (*material).get_bumpiness();
159 isSolid = (*material).get_solid();
161 // no material, assume solid
162 loadCapacity = DBL_MAX;
163 frictionFactor = 1.0;
164 rollingFriction = 0.02;
165 loadResistance = DBL_MAX;
169 _ground_frictionFactor = frictionFactor;
170 _ground_rollingFriction = rollingFriction;
171 _ground_loadCapacity = loadCapacity;
172 _ground_loadResistance = loadResistance;
173 _ground_bumpiness = bumpiness;
174 _ground_isSolid = isSolid;
180 void Gear::getPosition(float* out)
183 for(i=0; i<3; i++) out[i] = _pos[i];
186 void Gear::getCompression(float* out)
189 for(i=0; i<3; i++) out[i] = _cmpr[i];
192 void Gear::getGlobalGround(double* global_ground)
195 for(i=0; i<4; i++) global_ground[i] = _global_ground[i];
198 float Gear::getSpring()
203 float Gear::getDamping()
208 float Gear::getStaticFriction()
213 float Gear::getDynamicFriction()
218 float Gear::getBrake()
223 float Gear::getRotation()
228 float Gear::getExtension()
233 void Gear::getForce(float* force, float* contact)
235 Math::set3(_force, force);
236 Math::set3(_contact, contact);
244 float Gear::getCompressFraction()
249 bool Gear::getCastering()
254 bool Gear::getGroundIsSolid()
256 return _ground_isSolid;
259 float Gear::getBumpAltitude()
261 if (_ground_bumpiness<0.001) return 0.0;
262 double x = _global_x*0.1;
263 double y = _global_y*0.1;
268 //now x and y are in the range of 0..2pi
269 //we need a function, that is periodically on 2pi and gives some
270 //height. This is not very fast, but for a beginning.
271 //maybe this should be done by interpolating between some precalculated
273 float h = Math::sin(x)+Math::sin(7*x)+Math::sin(8*x)+Math::sin(13*x);
274 h += Math::sin(2*y)+Math::sin(5*y)+Math::sin(9*y*x)+Math::sin(17*y);
276 return h*(1/8.)*_ground_bumpiness*maxGroundBumpAmplitude;
279 void Gear::calcForce(RigidBody* body, State *s, float* v, float* rot)
281 // Init the return values
283 for(i=0; i<3; i++) _force[i] = _contact[i] = 0;
285 // Don't bother if it's not down
293 // Dont bother if we are in the "wrong" ground
294 if (!((_onWater&&!_ground_isSolid)||(_onSolid&&_ground_isSolid))) {
303 // The ground plane transformed to the local frame.
305 s->planeGlobalToLocal(_global_ground, ground);
307 // The velocity of the contact patch transformed to local coordinates.
309 s->velGlobalToLocal(_global_vel, glvel);
311 // First off, make sure that the gear "tip" is below the ground.
312 // If it's not, there's no force.
313 float a = ground[3] - Math::dot3(_pos, ground);
314 float BumpAltitude=0;
315 if (a<maxGroundBumpAmplitude)
317 BumpAltitude=getBumpAltitude();
330 // Now a is the distance from the tip to ground, so make b the
331 // distance from the base to ground. We can get the fraction
332 // (0-1) of compression from a/(a-b). Note the minus sign -- stuff
333 // above ground is negative.
335 Math::add3(_cmpr, _pos, tmp);
336 float b = ground[3] - Math::dot3(tmp, ground)+BumpAltitude;
338 // Calculate the point of ground _contact.
344 _contact[i] = _pos[i] + _frac*_cmpr[i];
346 // Turn _cmpr into a unit vector and a magnitude
348 float clen = Math::mag3(_cmpr);
349 Math::mul3(1/clen, _cmpr, cmpr);
351 // Now get the velocity of the point of contact
353 body->pointVelocity(_contact, rot, cv);
354 Math::add3(cv, v, cv);
355 Math::sub3(cv, glvel, cv);
357 // Finally, we can start adding up the forces. First the spring
358 // compression. (note the clamping of _frac to 1):
359 _frac = (_frac > 1) ? 1 : _frac;
361 // Add the initial load to frac, but with continous transistion around 0
362 float frac_with_initial_load;
363 if (_frac>0.2 || _initialLoad==0.0)
364 frac_with_initial_load = _frac+_initialLoad;
366 frac_with_initial_load = (_frac+_initialLoad)
367 *_frac*_frac*3*25-_frac*_frac*_frac*2*125;
369 float fmag = frac_with_initial_load*clen*_spring;
370 if (_speed_planing>0)
372 float v = Math::mag3(cv);
373 if (v < _speed_planing)
375 float frac = v/_speed_planing;
376 fmag = fmag*_spring_factor_not_planing*(1-frac)+fmag*frac;
379 // Then the damping. Use the only the velocity into the ground
380 // (projection along "ground") projected along the compression
381 // axis. So Vdamp = ground*(ground dot cv) dot cmpr
382 Math::mul3(Math::dot3(ground, cv), ground, tmp);
383 float dv = Math::dot3(cmpr, tmp);
384 float damp = _damp * dv;
385 if(damp > fmag) damp = fmag; // can't pull the plane down!
386 if(damp < -fmag) damp = -fmag; // sanity
388 // The actual force applied is only the component perpendicular to
389 // the ground. Side forces come from velocity only.
390 _wow = (fmag - damp) * -Math::dot3(cmpr, ground);
391 Math::mul3(-_wow, ground, _force);
393 // Wheels are funky. Split the velocity along the ground plane
394 // into rolling and skidding components. Assuming small angles,
395 // we generate "forward" and "left" unit vectors (the compression
396 // goes "up") for the gear, make a "steer" direction from these,
397 // and then project it onto the ground plane. Project the
398 // velocity onto the ground plane too, and extract the "steer"
399 // component. The remainder is the skid velocity.
401 float gup[3]; // "up" unit vector from the ground
402 Math::set3(ground, gup);
403 Math::mul3(-1, gup, gup);
405 float xhat[] = {1,0,0};
406 float steer[3], skid[3];
407 Math::cross3(gup, xhat, skid); // up cross xhat =~ skid
408 Math::unit3(skid, skid); // == skid
410 Math::cross3(skid, gup, steer); // skid cross up == steer
413 // Correct for a rotation
414 float srot = Math::sin(_rot);
415 float crot = Math::cos(_rot);
418 steer[0] = crot*tx + srot*ty;
419 steer[1] = -srot*tx + crot*ty;
423 skid[0] = crot*tx + srot*ty;
424 skid[1] = -srot*tx + crot*ty;
427 float vsteer = Math::dot3(cv, steer);
428 float vskid = Math::dot3(cv, skid);
429 float wgt = Math::dot3(_force, gup); // force into the ground
432 _rollSpeed = Math::sqrt(vsteer*vsteer + vskid*vskid);
433 // Don't modify caster angle when the wheel isn't moving,
434 // or else the angle will animate the "jitter" of a stopped
436 if(_rollSpeed > 0.05)
437 _casterAngle = Math::atan2(vskid, vsteer);
446 fsteer = (_brake * _ground_frictionFactor
447 +(1-_brake)*_ground_rollingFriction
448 )*calcFriction(wgt, vsteer);
449 fskid = calcFriction(wgt, vskid)*(_ground_frictionFactor);
453 fsteer = calcFrictionFluid(wgt, vsteer)*_ground_frictionFactor;
454 fskid = 10*calcFrictionFluid(wgt, vskid)*_ground_frictionFactor;
455 //factor 10: floats have different drag in x and y.
457 if(vsteer > 0) fsteer = -fsteer;
458 if(vskid > 0) fskid = -fskid;
460 //reduce friction if wanted by _reduceFrictionByExtension
461 float factor = (1-_frac)*(1-_reduceFrictionByExtension)+_frac*1;
462 factor = Math::clamp(factor,0,1);
466 // Phoo! All done. Add it up and get out of here.
467 Math::mul3(fsteer, steer, tmp);
468 Math::add3(tmp, _force, _force);
470 Math::mul3(fskid, skid, tmp);
471 Math::add3(tmp, _force, _force);
474 float Gear::calcFriction(float wgt, float v) //used on solid ground
476 // How slow is stopped? 10 cm/second?
477 const float STOP = 0.1f;
478 const float iSTOP = 1.0f/STOP;
480 if(v < STOP) return v*iSTOP * wgt * _sfric;
481 else return wgt * _dfric;
484 float Gear::calcFrictionFluid(float wgt, float v) //used on fluid ground
486 // How slow is stopped? 1 cm/second?
487 const float STOP = 0.01f;
488 const float iSTOP = 1.0f/STOP;
490 if(v < STOP) return v*iSTOP * wgt * _sfric;
491 else return wgt * _dfric*v*v*0.01;
492 //*0.01: to get _dfric of the same size than _dfric on solid
494 }; // namespace yasim