Game/GigLine/Source/GigLine/GigLineVehicle.cpp

@@ -233,8 +233,25 @@ void AGigLineVehicle::BeginPlay()
 				BodyComp->bHiddenInGame ? 1 : 0,
 				*BodyComp->Bounds.BoxExtent.ToString());
 		}
+		// Name the bones and check each setup against them: Chaos silently creates no wheel
+		// when a setup's bone is not on the mesh, which is how four setups produced zero
+		// wheels without a warning.
+		if (USkeletalMeshComponent* Body = GetMesh())
+		{
+			TArray<FName> Bones;
+			Body->GetBoneNames(Bones);
+			UE_LOG(LogTemp, Warning, TEXT("GigLine vehicle: %d bones, e.g. %s"),
+				Bones.Num(),
+				Bones.Num() > 0 ? *Bones[FMath::Min(1, Bones.Num() - 1)].ToString() : TEXT("none"));
+			for (const FChaosWheelSetup& Setup : Movement->WheelSetups)
+			{
+				UE_LOG(LogTemp, Warning, TEXT("GigLine vehicle: setup bone '%s' index %d"),
+					*Setup.BoneName.ToString(), Body->GetBoneIndex(Setup.BoneName));
+			}
+		}
 		UE_LOG(LogTemp, Warning,
-			TEXT("GigLine vehicle: %d wheel objects after register, torque %.0f"),
+			TEXT("GigLine vehicle: %d wheel objects at BeginPlay (wheels are created later, "
+			     "with the physics state), torque %.0f"),
 			Movement->Wheels.Num(), Movement->EngineSetup.MaxTorque);
 	}
 	UE_LOG(LogTemp, Warning, TEXT("GigLine vehicle: spawned at (%.0f, %.0f, %.0f), %d wheel setups"),
@@ -285,6 +302,13 @@ void AGigLineVehicle::Tick(float DeltaSeconds)
 	if (!bSettleReported && SettleElapsed > 3.0f)
 	{
 		bSettleReported = true;
+		if (const UChaosWheeledVehicleMovementComponent* Wheeled =
+				Cast<UChaosWheeledVehicleMovementComponent>(GetVehicleMovementComponent()))
+		{
+			UE_LOG(LogTemp, Warning,
+				TEXT("GigLine vehicle: %d wheel objects once physics exists"),
+				Wheeled->Wheels.Num());
+		}
 		if (UWorld* World = GetWorld())
 		{
 			FHitResult Hit;

Tools/ue_build_demo_map.py

@@ -700,6 +700,16 @@ def build():
     vehicle_origin = unreal.Vector(-12950.0, -900.0, 367.0)
     vehicle_rotation = unreal.Rotator(pitch=0.0, yaw=0.0, roll=0.0)
 
+    # The physics pawn: Chaos needs it even while the visible car is a set of plain
+    # panels, because that is the component that owns the wheels and the movement.
+    vehicle_class = unreal.load_class(None, "/Script/GigLine.GigLineVehicle")
+    if vehicle_class:
+        pawn = spawn(vehicle_class, vehicle_origin, "Demo_Vehicle_Sedan")
+        log(f"staged: Demo_Vehicle_Sedan ({'ok' if pawn else 'FAILED'})")
+    else:
+        log("staged: Demo_Vehicle_Sedan skipped - class not found")
+
+
     panel_systems = (
         "SM_Vehicle_Body",
         "SM_Vehicle_Trim",