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Fix suspension force calculation in VehicleBody3D to accurately follow Hooke's Law #112518

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Fix suspension force calculation in VehicleBody3D to accurately follow Hooke's Law #112518

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11 changes: 5 additions & 6 deletions scene/3d/physics/vehicle_body_3d.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -542,8 +542,6 @@ real_t VehicleBody3D::_ray_cast(int p_idx, PhysicsDirectBodyState3D *s) {
}

void VehicleBody3D::_update_suspension(PhysicsDirectBodyState3D *s) {
real_t chassisMass = get_mass();

for (int w_it = 0; w_it < wheels.size(); w_it++) {
VehicleWheel3D &wheel_info = *wheels[w_it];

Expand All @@ -555,8 +553,8 @@ void VehicleBody3D::_update_suspension(PhysicsDirectBodyState3D *s) {
real_t current_length = wheel_info.m_raycastInfo.m_suspensionLength;

real_t length_diff = (susp_length - current_length);

force = wheel_info.m_suspensionStiffness * length_diff * wheel_info.m_clippedInvContactDotSuspension;
//stiffness * 1000.0 to convert from N/mm to N/m
force = wheel_info.m_suspensionStiffness * 1000.0 * length_diff * wheel_info.m_clippedInvContactDotSuspension;
}

// Damper
Expand All @@ -569,12 +567,13 @@ void VehicleBody3D::_update_suspension(PhysicsDirectBodyState3D *s) {
} else {
susp_damping = wheel_info.m_wheelsDampingRelaxation;
}
force -= susp_damping * projected_rel_vel;
//damper * 1000.0 to convert from N/mm/s to N/m/s
force -= susp_damping * 1000.0 * projected_rel_vel;
}
}

// RESULT
wheel_info.m_wheelsSuspensionForce = force * chassisMass;
wheel_info.m_wheelsSuspensionForce = force;
if (wheel_info.m_wheelsSuspensionForce < real_t(0.)) {
wheel_info.m_wheelsSuspensionForce = real_t(0.);
}
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