How to set inertia manually with chaos engine

Development World Creation
, , , , ,
1

Hi, I would like to set the inertia tensor of physics body manually to do an accurate simulation.

For PhysX, I found that there is no function in components to directly do this, but I can directly interact with PhysX through this API(FPhysicsInterface_PhysX::SetMassSpaceInertiaTensor_AssumesLocked | Unreal Engine Documentation); and at here ([PHYSICS] Center of mass needs a rework - #9 by BoredEngineer), the function UMMTBPFunctionLibrary::MMTSetInertiaTensor is a sample to use it.

However, for chaos physics engine, I cannot find an equivalent API. How should I set the inertia tensor manually for chaos?

2

To explicitly set the inertia tensor for a rigid body, you can call the Physics Interface with FPhysicsInterface::SetMassSpaceInertiaTensor_AssumesLocked(Actor, MassSpaceInertiaTensor).
If you check for example inside the Chaos Vehicles source code, this is what it is used within UpdateMassProperties.

void UChaosVehicleMovementComponent::UpdateMassProperties(FBodyInstance* BodyInstance)
    {
    	if (BodyInstance && FPhysicsInterface::IsValid(BodyInstance->ActorHandle) && FPhysicsInterface::IsRigidBody(BodyInstance->ActorHandle))
    	{
    		FPhysicsCommand::ExecuteWrite(BodyInstance->ActorHandle, [&](FPhysicsActorHandle& Actor)
    			{
    				const float MassRatio = this->Mass > 0.0f ? this->Mass / BodyInstance->GetBodyMass() : 1.0f;
    
    				FVector InertiaTensor = BodyInstance->GetBodyInertiaTensor();
    
    				InertiaTensor.X *= this->InertiaTensorScale.X * MassRatio;
    				InertiaTensor.Y *= this->InertiaTensorScale.Y * MassRatio;
    				InertiaTensor.Z *= this->InertiaTensorScale.Z * MassRatio;
    
    				FPhysicsInterface::SetMassSpaceInertiaTensor_AssumesLocked(Actor, InertiaTensor);
    				FPhysicsInterface::SetMass_AssumesLocked(Actor, this->Mass);
    			});
    	}
    
    }