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
289 // Dont bother if we are in the "wrong" ground
290 if (!((_onWater&&!_ground_isSolid)||(_onSolid&&_ground_isSolid))) {
299 // The ground plane transformed to the local frame.
301 s->planeGlobalToLocal(_global_ground, ground);
303 // The velocity of the contact patch transformed to local coordinates.
305 s->velGlobalToLocal(_global_vel, glvel);
307 // First off, make sure that the gear "tip" is below the ground.
308 // If it's not, there's no force.
309 float a = ground[3] - Math::dot3(_pos, ground);
310 float BumpAltitude=0;
311 if (a<maxGroundBumpAmplitude)
313 BumpAltitude=getBumpAltitude();
326 // Now a is the distance from the tip to ground, so make b the
327 // distance from the base to ground. We can get the fraction
328 // (0-1) of compression from a/(a-b). Note the minus sign -- stuff
329 // above ground is negative.
331 Math::add3(_cmpr, _pos, tmp);
332 float b = ground[3] - Math::dot3(tmp, ground)+BumpAltitude;
334 // Calculate the point of ground _contact.
340 _contact[i] = _pos[i] + _frac*_cmpr[i];
342 // Turn _cmpr into a unit vector and a magnitude
344 float clen = Math::mag3(_cmpr);
345 Math::mul3(1/clen, _cmpr, cmpr);
347 // Now get the velocity of the point of contact
349 body->pointVelocity(_contact, rot, cv);
350 Math::add3(cv, v, cv);
351 Math::sub3(cv, glvel, cv);
353 // Finally, we can start adding up the forces. First the spring
354 // compression. (note the clamping of _frac to 1):
355 _frac = (_frac > 1) ? 1 : _frac;
357 // Add the initial load to frac, but with continous transistion around 0
358 float frac_with_initial_load;
359 if (_frac>0.2 || _initialLoad==0.0)
360 frac_with_initial_load = _frac+_initialLoad;
362 frac_with_initial_load = (_frac+_initialLoad)
363 *_frac*_frac*3*25-_frac*_frac*_frac*2*125;
365 float fmag = frac_with_initial_load*clen*_spring;
366 if (_speed_planing>0)
368 float v = Math::mag3(cv);
369 if (v < _speed_planing)
371 float frac = v/_speed_planing;
372 fmag = fmag*_spring_factor_not_planing*(1-frac)+fmag*frac;
375 // Then the damping. Use the only the velocity into the ground
376 // (projection along "ground") projected along the compression
377 // axis. So Vdamp = ground*(ground dot cv) dot cmpr
378 Math::mul3(Math::dot3(ground, cv), ground, tmp);
379 float dv = Math::dot3(cmpr, tmp);
380 float damp = _damp * dv;
381 if(damp > fmag) damp = fmag; // can't pull the plane down!
382 if(damp < -fmag) damp = -fmag; // sanity
384 // The actual force applied is only the component perpendicular to
385 // the ground. Side forces come from velocity only.
386 _wow = (fmag - damp) * -Math::dot3(cmpr, ground);
387 Math::mul3(-_wow, ground, _force);
389 // Wheels are funky. Split the velocity along the ground plane
390 // into rolling and skidding components. Assuming small angles,
391 // we generate "forward" and "left" unit vectors (the compression
392 // goes "up") for the gear, make a "steer" direction from these,
393 // and then project it onto the ground plane. Project the
394 // velocity onto the ground plane too, and extract the "steer"
395 // component. The remainder is the skid velocity.
397 float gup[3]; // "up" unit vector from the ground
398 Math::set3(ground, gup);
399 Math::mul3(-1, gup, gup);
401 float xhat[] = {1,0,0};
402 float steer[3], skid[3];
403 Math::cross3(gup, xhat, skid); // up cross xhat =~ skid
404 Math::unit3(skid, skid); // == skid
406 Math::cross3(skid, gup, steer); // skid cross up == steer
409 // Correct for a rotation
410 float srot = Math::sin(_rot);
411 float crot = Math::cos(_rot);
414 steer[0] = crot*tx + srot*ty;
415 steer[1] = -srot*tx + crot*ty;
419 skid[0] = crot*tx + srot*ty;
420 skid[1] = -srot*tx + crot*ty;
423 float vsteer = Math::dot3(cv, steer);
424 float vskid = Math::dot3(cv, skid);
425 float wgt = Math::dot3(_force, gup); // force into the ground
428 _rollSpeed = Math::sqrt(vsteer*vsteer + vskid*vskid);
429 // Don't modify caster angle when the wheel isn't moving,
430 // or else the angle will animate the "jitter" of a stopped
432 if(_rollSpeed > 0.05)
433 _casterAngle = Math::atan2(vskid, vsteer);
442 fsteer = (_brake * _ground_frictionFactor
443 +(1-_brake)*_ground_rollingFriction
444 )*calcFriction(wgt, vsteer);
445 fskid = calcFriction(wgt, vskid)*(_ground_frictionFactor);
449 fsteer = calcFrictionFluid(wgt, vsteer)*_ground_frictionFactor;
450 fskid = 10*calcFrictionFluid(wgt, vskid)*_ground_frictionFactor;
451 //factor 10: floats have different drag in x and y.
453 if(vsteer > 0) fsteer = -fsteer;
454 if(vskid > 0) fskid = -fskid;
456 //reduce friction if wanted by _reduceFrictionByExtension
457 float factor = (1-_frac)*(1-_reduceFrictionByExtension)+_frac*1;
458 factor = Math::clamp(factor,0,1);
462 // Phoo! All done. Add it up and get out of here.
463 Math::mul3(fsteer, steer, tmp);
464 Math::add3(tmp, _force, _force);
466 Math::mul3(fskid, skid, tmp);
467 Math::add3(tmp, _force, _force);
470 float Gear::calcFriction(float wgt, float v) //used on solid ground
472 // How slow is stopped? 10 cm/second?
473 const float STOP = 0.1f;
474 const float iSTOP = 1.0f/STOP;
476 if(v < STOP) return v*iSTOP * wgt * _sfric;
477 else return wgt * _dfric;
480 float Gear::calcFrictionFluid(float wgt, float v) //used on fluid ground
482 // How slow is stopped? 1 cm/second?
483 const float STOP = 0.01f;
484 const float iSTOP = 1.0f/STOP;
486 if(v < STOP) return v*iSTOP * wgt * _sfric;
487 else return wgt * _dfric*v*v*0.01;
488 //*0.01: to get _dfric of the same size than _dfric on solid
490 }; // namespace yasim