With all our meshes done, we should make sure things are parented and ordered properly in the hierarchy, ready for being placed in the game.

Place transforms and order your hierarchy

At minimum, you’ll need at least the following:

• An empty with your part name. Parent your main engine mesh to it.
• An empty named gimbal. The config uses this to determine the location of where your engine nozzle pivots when gimballing, if your engine has gimbal. Due to weird coordinate translations between Blender and KSP/Unity, rotate it so that its Y-direction is facing downwards. The gimbal empty should be parented to the main part empty, and the engine nozzle should be parented to the gimbal empty.
• An empty named thrustTransform. This is where the thrust of your engine comes from and what direction it travels in. Rotate it so that the Z-direction is facing downwards, and position its origin so that it’s aligned right with the nozzle of the engine. Parent it to gimbal. Note this will also determine where the Waterfall plume will be placed, if you want one.

It’s a lot to keep track of, but the RCS Build Aid mod can help you in the VAB to identify off-centre or incorrectly oriented thrust transforms.

Generate colliders

Colliders both determine how the object should behave in rigidbody physics, as well as determining the “hover area” when interacting with the part in the VAB/SPH.

For each seperate mesh object in your part, select it, head into the active tools tab, and click one of the options (usually Single Collider: Mesh) to generate a collider. The tool will automatically parent and name the collider properly for you; you could probably just hide it from the hierarchy at this point.

Define stack attachment points

You’ll want two empties, one for the top and bottom attachment nodes each. Name them node_stack_bottom and node_stack_top. Make sure the bottom node empty is pointing downwards—using the “single arrow” empty type is helpful for gauging orientation.

Both of these should be parented directly to the main part empty.

These empties and their names will be used by the config to define attachment nodes. You should also adjust the size of each node, in the object data pane:

Set up your engine shroud

If you have a custom engine shroud, its mesh should be parented to the main part empty. To make sure it doesn’t show up in the icon preview in the VAB/SPH, head to the object properties tab, find the Mu Properties rollout, and set Tag to Icon_Hidden. It will also need its own collider too.

Note that if you either: