I've set up a vehicle simulation. I based it on the vehicle demo that comes with Bullet. I have the suspension stiffness set extremely high, so the wheels are very rigid and won't more up and down as the terrain changes. When I try to adjust each wheel's m_suspensionStiffness, m_wheelsDampingRelaxation, and m_wheelsDampingCompression to allow the wheels to "give", the wheels simply sink into the ground until the bottom of the chassis is resting on the ground, at which point the vehicle obviously can't move. Can someone help me understand exactly how I should be adjusting these parameters to allow the wheels to move up and down as they do in the demo? Is there a tutorial out there explaining how to use the vehicle parameters? I've included the code I feel is relevant below. Sorry, I know it's kind of sloppy, but I've been tearing it apart trying to figure this out. Thank you very much.
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float gEngineForce = 0.f;
float gBrakingForce = 0.f;
float maxEngineForce = 1000.f;//this should be engine/velocity dependent
float maxBrakingForce = 1000.f;
float gVehicleSteering = 0.0f;
float steeringIncrement = 0.06f;
float steeringClamp = .6f;
float wheelRadius = .436f;
float wheelWidth = 0.3f;
float wheelFriction = 1000.0f;
float suspensionStiffness = 10000.0f;
float suspensionDamping = 10.3f;
float suspensionCompression = 20.4f;
float rollInfluence = 1.0f;
int rightIndex = 0;
int upIndex = 1;
int forwardIndex = 2;
btVector3 wheelDirectionCS0(0,-1,0);
btVector3 wheelAxleCS(-1,0,0);
//other irrelivant code...
btCollisionShape* chassisShape = new btBoxShape(btVector3(0.8f, 0.4f, 2.0f));
btCompoundShape* compound = new btCompoundShape();
btTransform localTrans;
localTrans.setIdentity();
//localTrans effectively shifts the center of mass with respect to the chassis
localTrans.setOrigin(btVector3(0,0,0));
compound->addChildShape(localTrans,chassisShape);
btVector3 inertia;
compound->calculateLocalInertia(200.0f, inertia);
btMotionState * s = new btDefaultMotionState();
btMatrix3x3 m;
m.setIdentity();
s->setWorldTransform(btTransform(m, btVector3(5,3,-12)));
v->chassis = new btRigidBody(200.0f, s, compound, inertia, 0, 0, 1000, 0);
physics_world->addRigidBody(v->chassis);
v->chassis->setLinearVelocity(btVector3(0,0,0));
v->chassis->setAngularVelocity(btVector3(0,0,0));
v->raycaster = new btDefaultVehicleRaycaster(physics_world);
v->vehicle = new btRaycastVehicle(v->tuning, v->chassis, v->raycaster);
///never deactivate the vehicle
v->chassis->setActivationState(DISABLE_DEACTIVATION);
physics_world->addVehicle(v->vehicle);
float connectionHeight = -0.35f;
bool isFrontWheel=true;
//choose coordinate system
v->vehicle->setCoordinateSystem(rightIndex,upIndex,forwardIndex);
float x = .85f;
btVector3 connectionPointCS0(x,connectionHeight,1.5f);
v->vehicle->addWheel(connectionPointCS0,wheelDirectionCS0,wheelAxleCS,suspensionRestLength,wheelRadius,v->tuning,isFrontWheel);
connectionPointCS0 = btVector3(-x,connectionHeight,1.5f);
v->vehicle->addWheel(connectionPointCS0,wheelDirectionCS0,wheelAxleCS,suspensionRestLength,wheelRadius,v->tuning,isFrontWheel);
connectionPointCS0 = btVector3(-x,connectionHeight,-1.5f);
isFrontWheel = false;
v->vehicle->addWheel(connectionPointCS0,wheelDirectionCS0,wheelAxleCS,suspensionRestLength,wheelRadius,v->tuning,isFrontWheel);
connectionPointCS0 = btVector3(x,connectionHeight,-1.5f);
v->vehicle->addWheel(connectionPointCS0,wheelDirectionCS0,wheelAxleCS,suspensionRestLength,wheelRadius,v->tuning,isFrontWheel);
int i;
for (i=0;i<v->vehicle->getNumWheels();i++)
{
btWheelInfo& wheel = v->vehicle->getWheelInfo(i);
wheel.m_suspensionStiffness = suspensionStiffness;
wheel.m_wheelsDampingRelaxation = suspensionDamping;
wheel.m_wheelsDampingCompression = suspensionCompression;
wheel.m_frictionSlip = wheelFriction;
wheel.m_rollInfluence = rollInfluence;
}
//more irrelivant code...
