/// Update the state of this tire system at the current time.
/// The tire system is provided the current state of its associated wheel and
/// a handle to the terrain system.
public virtual void Synchronize(double time, ///< [in] current time
ChSubsysDefs.WheelState wheel_state, ///< [in] current state of associated wheel body
RigidTerrain terrain ///< [in] reference to the terrain system
)
{
CalculateKinematics(time, wheel_state, terrain);
}
public virtual void FixedUpdate()
{
m_wheelState = GetWheelState();
m_wheel.Empty_forces_accumulators();
m_wheel.Accumulate_force(m_tireforce.force, m_tireforce.point, false);
m_wheel.Accumulate_torque(m_tireforce.moment, false);
}
/// Calculate kinematics quantities based on the current state of the associated
/// wheel body.
public void CalculateKinematics(double time, ///< [in] current time
ChSubsysDefs.WheelState state, ///< [in] current state of associated wheel body
RigidTerrain terrain ///< [in] reference to the terrain system
)
{
// Wheel normal (expressed in global frame)
ChVector wheel_normal = state.rot.GetYaxis();
// Terrain normal at wheel location (expressed in global frame)
ChVector Z_dir = terrain.GetNormal(state.pos.x, state.pos.y);
// Longitudinal (heading) and lateral directions, in the terrain plane
ChVector X_dir = ChVector.Vcross(wheel_normal, Z_dir);
X_dir.Normalize();
ChVector Y_dir = ChVector.Vcross(Z_dir, X_dir);
// Tire reference coordinate system
// ChMatrix33<double> rot = new ChMatrix33<double>(0); // Needs nesting
rot.Set_A_axis(X_dir, Y_dir, Z_dir);
ChCoordsys tire_csys = new ChCoordsys(state.pos, rot.Get_A_quaternion());
// Express wheel linear velocity in tire frame
ChVector V = tire_csys.TransformDirectionParentToLocal(state.lin_vel);
// Express wheel normal in tire frame
ChVector n = tire_csys.TransformDirectionParentToLocal(wheel_normal);
// Slip angle
double abs_Vx = Mathfx.Abs(V.x);
double zero_Vx = 1e-4;
m_slip_angle = (abs_Vx > zero_Vx) ? Math.Atan(V.y / abs_Vx) : 0;
// Longitudinal slip
m_longitudinal_slip = (abs_Vx > zero_Vx) ? -(V.x - state.omega * GetRadius()) / abs_Vx : 0;
// Camber angle
m_camber_angle = Math.Atan2(n.z, n.y);
}
