7 #include "BodyEnvironment.hpp"
8 #include "RigidBody.hpp"
11 #include <simgear/bvh/BVHMaterial.hxx>
12 #include <FDM/flight.hxx>
15 static const float YASIM_PI = 3.14159265358979323846;
16 static const float maxGroundBumpAmplitude=0.4;
17 //Amplitude can be positive and negative
23 _pos[i] = _cmpr[i] = 0;
34 _ground_frictionFactor = 1;
35 _ground_rollingFriction = 0.02;
36 _ground_loadCapacity = 1e30;
37 _ground_loadResistance = 1e30;
39 _ground_bumpiness = 0;
44 _reduceFrictionByExtension = 0;
45 _spring_factor_not_planing = 1;
48 _ignoreWhileSolving = 0;
51 _global_ground[i] = _global_vel[i] = 0;
52 _global_ground[2] = 1;
53 _global_ground[3] = -1e3;
56 void Gear::setPosition(float* position)
59 for(i=0; i<3; i++) _pos[i] = position[i];
62 void Gear::setCompression(float* compression)
65 for(i=0; i<3; i++) _cmpr[i] = compression[i];
68 void Gear::setSpring(float spring)
73 void Gear::setDamping(float damping)
78 void Gear::setStaticFriction(float sfric)
83 void Gear::setDynamicFriction(float dfric)
88 void Gear::setBrake(float brake)
90 _brake = Math::clamp(brake, 0, 1);
93 void Gear::setRotation(float rotation)
98 void Gear::setExtension(float extension)
100 _extension = Math::clamp(extension, 0, 1);
103 void Gear::setCastering(bool c)
108 void Gear::setContactPoint(bool c)
113 void Gear::setOnWater(bool c)
118 void Gear::setOnSolid(bool c)
123 void Gear::setIgnoreWhileSolving(bool c)
125 _ignoreWhileSolving = c;
128 void Gear::setSpringFactorNotPlaning(float f)
130 _spring_factor_not_planing = f;
133 void Gear::setSpeedPlaning(float s)
138 void Gear::setReduceFrictionByExtension(float s)
140 _reduceFrictionByExtension = s;
143 void Gear::setInitialLoad(float l)
148 void Gear::setGlobalGround(double *global_ground, float* global_vel,
149 double globalX, double globalY,
150 const simgear::BVHMaterial *material)
153 double frictionFactor,rollingFriction,loadCapacity,loadResistance,bumpiness;
156 for(i=0; i<4; i++) _global_ground[i] = global_ground[i];
157 for(i=0; i<3; i++) _global_vel[i] = global_vel[i];
160 loadCapacity = (*material).get_load_resistance();
161 frictionFactor =(*material).get_friction_factor();
162 rollingFriction = (*material).get_rolling_friction();
163 loadResistance = (*material).get_load_resistance();
164 bumpiness = (*material).get_bumpiness();
165 isSolid = (*material).get_solid();
167 // no material, assume solid
168 loadCapacity = DBL_MAX;
169 frictionFactor = 1.0;
170 rollingFriction = 0.02;
171 loadResistance = DBL_MAX;
175 _ground_frictionFactor = frictionFactor;
176 _ground_rollingFriction = rollingFriction;
177 _ground_loadCapacity = loadCapacity;
178 _ground_loadResistance = loadResistance;
179 _ground_bumpiness = bumpiness;
180 _ground_isSolid = isSolid;
186 void Gear::getPosition(float* out)
189 for(i=0; i<3; i++) out[i] = _pos[i];
192 void Gear::getCompression(float* out)
195 for(i=0; i<3; i++) out[i] = _cmpr[i];
198 void Gear::getGlobalGround(double* global_ground)
201 for(i=0; i<4; i++) global_ground[i] = _global_ground[i];
204 float Gear::getSpring()
209 float Gear::getDamping()
214 float Gear::getStaticFriction()
219 float Gear::getDynamicFriction()
224 float Gear::getBrake()
229 float Gear::getRotation()
234 float Gear::getExtension()
239 void Gear::getForce(float* force, float* contact)
241 Math::set3(_force, force);
242 Math::set3(_contact, contact);
250 float Gear::getCompressFraction()
255 bool Gear::getCastering()
260 bool Gear::getGroundIsSolid()
262 return _ground_isSolid;
265 float Gear::getBumpAltitude()
267 if (_ground_bumpiness<0.001) return 0.0;
268 double x = _global_x*0.1;
269 double y = _global_y*0.1;
274 //now x and y are in the range of 0..2pi
275 //we need a function, that is periodically on 2pi and gives some
276 //height. This is not very fast, but for a beginning.
277 //maybe this should be done by interpolating between some precalculated
279 float h = Math::sin(x)+Math::sin(7*x)+Math::sin(8*x)+Math::sin(13*x);
280 h += Math::sin(2*y)+Math::sin(5*y)+Math::sin(9*y*x)+Math::sin(17*y);
282 return h*(1/8.)*_ground_bumpiness*maxGroundBumpAmplitude;
285 void Gear::calcForce(RigidBody* body, State *s, float* v, float* rot)
287 // Init the return values
289 for(i=0; i<3; i++) _force[i] = _contact[i] = 0;
291 // Don't bother if it's not down
299 // Dont bother if we are in the "wrong" ground
300 if (!((_onWater&&!_ground_isSolid)||(_onSolid&&_ground_isSolid))) {
309 // The ground plane transformed to the local frame.
311 s->planeGlobalToLocal(_global_ground, ground);
313 // The velocity of the contact patch transformed to local coordinates.
315 s->velGlobalToLocal(_global_vel, glvel);
317 // First off, make sure that the gear "tip" is below the ground.
318 // If it's not, there's no force.
319 float a = ground[3] - Math::dot3(_pos, ground);
320 float BumpAltitude=0;
321 if (a<maxGroundBumpAmplitude)
323 BumpAltitude=getBumpAltitude();
336 // Now a is the distance from the tip to ground, so make b the
337 // distance from the base to ground. We can get the fraction
338 // (0-1) of compression from a/(a-b). Note the minus sign -- stuff
339 // above ground is negative.
341 Math::add3(_cmpr, _pos, tmp);
342 float b = ground[3] - Math::dot3(tmp, ground)+BumpAltitude;
344 // Calculate the point of ground _contact.
350 _contact[i] = _pos[i] + _frac*_cmpr[i];
352 // Turn _cmpr into a unit vector and a magnitude
354 float clen = Math::mag3(_cmpr);
355 Math::mul3(1/clen, _cmpr, cmpr);
357 // Now get the velocity of the point of contact
359 body->pointVelocity(_contact, rot, cv);
360 Math::add3(cv, v, cv);
361 Math::sub3(cv, glvel, cv);
363 // Finally, we can start adding up the forces. First the spring
364 // compression. (note the clamping of _frac to 1):
365 _frac = (_frac > 1) ? 1 : _frac;
367 // Add the initial load to frac, but with continous transistion around 0
368 float frac_with_initial_load;
369 if (_frac>0.2 || _initialLoad==0.0)
370 frac_with_initial_load = _frac+_initialLoad;
372 frac_with_initial_load = (_frac+_initialLoad)
373 *_frac*_frac*3*25-_frac*_frac*_frac*2*125;
375 float fmag = frac_with_initial_load*clen*_spring;
376 if (_speed_planing>0)
378 float v = Math::mag3(cv);
379 if (v < _speed_planing)
381 float frac = v/_speed_planing;
382 fmag = fmag*_spring_factor_not_planing*(1-frac)+fmag*frac;
385 // Then the damping. Use the only the velocity into the ground
386 // (projection along "ground") projected along the compression
387 // axis. So Vdamp = ground*(ground dot cv) dot cmpr
388 Math::mul3(Math::dot3(ground, cv), ground, tmp);
389 float dv = Math::dot3(cmpr, tmp);
390 float damp = _damp * dv;
391 if(damp > fmag) damp = fmag; // can't pull the plane down!
392 if(damp < -fmag) damp = -fmag; // sanity
394 // The actual force applied is only the component perpendicular to
395 // the ground. Side forces come from velocity only.
396 _wow = (fmag - damp) * -Math::dot3(cmpr, ground);
397 Math::mul3(-_wow, ground, _force);
399 // Wheels are funky. Split the velocity along the ground plane
400 // into rolling and skidding components. Assuming small angles,
401 // we generate "forward" and "left" unit vectors (the compression
402 // goes "up") for the gear, make a "steer" direction from these,
403 // and then project it onto the ground plane. Project the
404 // velocity onto the ground plane too, and extract the "steer"
405 // component. The remainder is the skid velocity.
407 float gup[3]; // "up" unit vector from the ground
408 Math::set3(ground, gup);
409 Math::mul3(-1, gup, gup);
411 float xhat[] = {1,0,0};
412 float steer[3], skid[3];
413 Math::cross3(gup, xhat, skid); // up cross xhat =~ skid
414 Math::unit3(skid, skid); // == skid
416 Math::cross3(skid, gup, steer); // skid cross up == steer
419 // Correct for a rotation
420 float srot = Math::sin(_rot);
421 float crot = Math::cos(_rot);
424 steer[0] = crot*tx + srot*ty;
425 steer[1] = -srot*tx + crot*ty;
429 skid[0] = crot*tx + srot*ty;
430 skid[1] = -srot*tx + crot*ty;
433 float vsteer = Math::dot3(cv, steer);
434 float vskid = Math::dot3(cv, skid);
435 float wgt = Math::dot3(_force, gup); // force into the ground
438 _rollSpeed = Math::sqrt(vsteer*vsteer + vskid*vskid);
439 // Don't modify caster angle when the wheel isn't moving,
440 // or else the angle will animate the "jitter" of a stopped
442 if(_rollSpeed > 0.05)
443 _casterAngle = Math::atan2(vskid, vsteer);
452 fsteer = (_brake * _ground_frictionFactor
453 +(1-_brake)*_ground_rollingFriction
454 )*calcFriction(wgt, vsteer);
455 fskid = calcFriction(wgt, vskid)*(_ground_frictionFactor);
459 fsteer = calcFrictionFluid(wgt, vsteer)*_ground_frictionFactor;
460 fskid = 10*calcFrictionFluid(wgt, vskid)*_ground_frictionFactor;
461 //factor 10: floats have different drag in x and y.
463 if(vsteer > 0) fsteer = -fsteer;
464 if(vskid > 0) fskid = -fskid;
466 //reduce friction if wanted by _reduceFrictionByExtension
467 float factor = (1-_frac)*(1-_reduceFrictionByExtension)+_frac*1;
468 factor = Math::clamp(factor,0,1);
472 // Phoo! All done. Add it up and get out of here.
473 Math::mul3(fsteer, steer, tmp);
474 Math::add3(tmp, _force, _force);
476 Math::mul3(fskid, skid, tmp);
477 Math::add3(tmp, _force, _force);
480 float Gear::calcFriction(float wgt, float v) //used on solid ground
482 // How slow is stopped? 10 cm/second?
483 const float STOP = 0.1f;
484 const float iSTOP = 1.0f/STOP;
486 if(v < STOP) return v*iSTOP * wgt * _sfric;
487 else return wgt * _dfric;
490 float Gear::calcFrictionFluid(float wgt, float v) //used on fluid ground
492 // How slow is stopped? 1 cm/second?
493 const float STOP = 0.01f;
494 const float iSTOP = 1.0f/STOP;
496 if(v < STOP) return v*iSTOP * wgt * _sfric;
497 else return wgt * _dfric*v*v*0.01;
498 //*0.01: to get _dfric of the same size than _dfric on solid
500 }; // namespace yasim