Bone hierarchy in vehicle models

Basis bone

The basis bone serves as the root bone in the skeletal hierarchy of any vehicle model. It functions as a dummy helper that defines critical properties of the model, including:

• model type;

• export path for the model to the game;

• wheel rotation speed and size (applied if all wheels are uniformly sized; otherwise, sizes are set in individual wheel bones);

• inverse kinematics (IK) parameter IKType=revolute with rotation constraints, if the vehicle supports body rotation.

• animation type and duration for key sequences;

Example Object Properties window of the basis bone

Placement and orientation of the basis bone

• The basis bone is positioned at the origin point (X=0, Y=0, Z=0) in world space, ensuring the model aligns correctly within the game.

• In the "Front" orthographic view, the vehicle is displayed from the right side, which must be accounted for during configuration.

• The forward movement vector of the basis bone—and consequently the entire model—is aligned with the positive X-axis.

Example: Orientation of the basis bone in the "Front" orthographic view

Accurate orientation of the basis bone is vital for:

• proper alignment and movement of the model in the game space;

• correct placement and visualization of the selection circle sprite beneath the model.

Example: Selection circle alignment under a tank model when the unit is selected

Visible bones of the vehicle model

Visible bones of the model are the primary bones and secondary bones in the model's element hierarchy that contain the meshes of the model's components.

Primary bones

Primary bones represent the parent bones in the model element hierarchy, forming the primary part of the visible mesh of vehicle components:

• body (hull);

• turret;

• cabin;

• gun_rot (gun elevation mechanism);

• gun;

• engine;

• track and wheel (transmission bones).

Primary bones hierarchy scheme

basis
     ├── body
          ├── engine
          ├── cabin
          ├── turret
               ├── gun_rot
                    └── gun

Secondary bones

Secondary bones contain meshes of parts of a vehicle model's component :

• detail (visual detail);

• shield (additional armor part);

• enumerator (vehicle identifier);

• cover/door;

• bones associated with the vehicle's suspension mechanism.

Secondary bones are typically linked to the primary bones they are part of .

Bone properties

Properties of bones are defined in the Object Properties window.

Parameter	Description
poly	Defines bone visibility. Absence of this parameter makes the bone invisible.
ID=<value>	Component identifier. Links the bone to a specific vehicle component (e.g., Hull, Turret, Left track, Gun).
Animation=<name>	List of animations if the bone is animated
IKType=revolute, IKType=socket, IKSpeed=<value>, IKLimit=<value>.	Inverse kinematics parameters allow the bone to operate under IK rules, setting the speed and rotation limits for the bone.

Example of turret component properties

ID values for vehicle components

body	Hull
engine	Engine
cabin	Vehicle cabin
turret	Turret
gun	Gun
trackleft / trackright	Left /Right tracks
wheelright<N> / wheelleft<N>	Right and Left wheels (<N> is the wheel's index)

The ID value of secondary bones corresponds to the ID value of the primary bones of which they are a visual part.

Despite identical naming, a bone is not equivalent to a vehicle component.

A vehicle component can consist of multiple bones with different names but the same ID value. As a whole, bones with the same ID form a specific vehicle component in the game.

Examples:

• the bones turret, cover, and detail, each assigned the property ID=turret, together form the Turret component in the game;

• the bones body, cover, and detail, each assigned the property ID=body, together form the Hull component in the game.

Animation types for components

• break: destruction animation assigned to the bone of the intact part of the model, representing the undamaged vehicle component.

• repair: animation for repairing the х-model of a vehicle component.

For more details on configuring the hierarchy of visible bone elements, refer to the following articles:

The body bone

Turret

Gun

Transmission

Secondary bones

Engine

Helper bones

Helper bones are predominantly invisible dummy objects used to ensure the proper functioning of a model's visual, functional, and animation aspects.

Vision bones

• visor1: an invisible helper linked to the turret bone, representing the turret's field of view.

• visor2: an invisible helper acting as the "eyes" of the tank, aligned with the movement vector and linked to the body bone, positioned near the frontal armor's view slit.

These bones are aligned along the X-axis

Special effects bones

Special effect bones (effectors) are used to create visual effects in the game. These bones are aligned along the X-axis for correct effect orientation.

Effector name	Purpose	Naming rules and specifics
fxfire1	Engine fire effect	If multiple bones are needed, they are named sequentially (e.g., fxfire1, fxfire2, etc.).
fxfire2	Body fire effect	Similar naming convention as above.
fxfire3	Turret fire effect	The naming continues sequentially if additional bones are required.
fxshot	Dust effect from tank firing	This bone is used without variation in naming unless additional directional effects are required.
fxsmoke	Exhaust effects	For multiple exhaust effects, sequential numbering is added (e.g., fxsmoke1, fxsmoke2, etc.).
fxstop	Brake lights	If more than one brake light is needed, bones are named sequentially (e.g., fxstop1, fxstop2, etc.).
headlight	Headlight glow	If multiple headlights exist, side indices (L for left, R for right) are included in the names (e.g., headlightL).
fxlight	Additional headlight glow effects	Sequential numbering is added, but the first bone does not include a number (e.g., fxlight, fxlight1, fxlight2).
fxtrace	Dust and dirt from tracks or wheels	Bones are named sequentially with side indices (e.g., fxtraceL1, fxtraceR1, fxtraceL2, fxtraceR2).
foresight	Weapon or machine gun firing effects	If multiple effects are needed, the bones are numbered sequentially (e.g., foresight1, foresight2, etc.).

Bones for initiating human-to-vehicle boarding animations

To define animation entry points for human units boarding vehicles, special bones known as emit are utilized.

Name	Description
emit0, emit1, emit2	Primary bones defining entry points for animations of crew boarding directly into the tank: emit1 and emit2 are positioned on either side of the model near the turret, while emit0 is optional and used for a driver's hatch animation if present.
emit3, emit4, emit5, etc.	Bones defining points in space near the tank, marking positions for soldiers boarding the vehicle's armor as passengers.

Correct placement and orientation of emit bones for crew members and passengers boarding animations

Rules for emit bones

• The number of emit bones must match the animation requirements. Missing bones can cause incorrect unit behavior.

• The pivot orientation of emit bones should align along the X-axis towards the body bone for proper crew alignment.

• These bones remain invisible and do not require properties in the Object Properties window.

Bones for marking passenger seating positions

Invisible seat bones define the seating positions for passengers on the vehicle’s armor and mark the endpoints of boarding animations starting from emit bones.

seat01, seat02, etc.	Bones placed opposite their corresponding emit bones

Rules for seat bones

• The number of seat bones must match the emit bones for visible passengers.

• Proper positioning ensures realistic passenger animations.

• These bones remain invisible and do not require properties in the Object Properties window.

Bones for machine gun placement

Mounting points for machine guns on the vehicle are defined by special bones called mgun. These bones can be visible (containing polygons) or invisible (implemented as helper objects) and are linked to the specific model element intended for the machine gun.

Positioning of an invisible mgun bone

Properties of mgun bones

The properties of mgun bones are specified in the [Object Properties] window and can include the following parameters:

poly	Makes the bone visible. Should be applied if the machine gun mesh is part of the model. If the gun is hidden or only the mounting point is present, the bone remains invisible.
IKType=revolute	Enables inverse kinematics for rotational aiming.
IKMin=<value> IKMax=<value>	Defines the minimum/maximum rotation limit for inverse kinematics.

Properties of a mgun bone operating with inverse kinematics

Linking effectors to mgun bones

Helpers named foresight are linked to mgun bones to spawn machine gun firing effects along the X-axis.

Naming rule for mgun-foresight linkage

If the vehicle has multiple additional machine guns, the naming of the foresight helper must match the corresponding mgun bone:

• mgun → foresight3

• mgun1 → foresight4

• mgun2 → foresight5

• mgun3 → foresight6

Failure to follow the naming convention will result in script errors.

Configuring mgun bones

When modeling, it is essential to include a sufficient number of mgun bones to accommodate the maximum possible machine gun placements on the vehicle.

Machine gun type	Description
aa	Anti-aircraft gun
hull	Fixed machine gun mounted in the chassis
coaxial	Coaxial machine gun mounted in the turret
rear	Rear-mounted machine gun

The configuration for linking machine guns to bones is defined in the model's .def file within placer blocks.

Syntax:

{placer "mgun<N>" [...]}
Where <N> represents the sequential number of the mgun bone.

Example of the mgun bone description in a .def file of a vehicle model

{place "mgun2"  
  {type "coaxial"}  
  {weapon "dt_vh" filled}  
  {foresight "foresight5"}  
  {gunner "gunner"}  
  {charger "gunner"}  
  ("sequential_aim")  
  ("abm_mgun")  
  {basic}  
}

Volumes

A volume is a parametric shape (e.g., box, sphere, cylinder) or a mesh-based form (edit poly) that envelops the model's mesh and is used to calculate the physical interactions of the unit in the game.

Creation and configuration of volumes

Bones of the volume type are created for all major bones of the model. Each primary bone requires its own volume or a set of volumes.

It is unnecessary to create volumes for detail bones because the game engine does not support volumes for visual parts.

The shape of the volume mesh should ensure realistic physical interactions. The volume parameter must be set in the [Object Properties] of the volume. A Material ID is assigned to the polygons of the volume mesh, which determines armor penetration calculations.

Volumes should be extruded from a rectangle in the Top viewport. This ensures that Material IDs are automatically assigned to the volume surface, eliminating the need for additional verification or reassignment according to the established rules.

Volumes must remain standard primitives. Converting a primitive into polygonal forms using editable poly tools is recommended only when the complex geometry of a part of the model cannot be represented with a primitive.

Geometry adjustments at the sub-object level are permissible if the created model is not a single volume. In such cases, creating multiple volume bones with identical properties is allowed. There should be no gaps between such volumes; however, minor overlaps are acceptable.

Example of volumes for the Body and Engine

Examples of volume creation In the first screenshot, the volumes are created correctly. In the second screenshot, the volume is created incorrectly as it obstructs projectiles/bullets from hitting units located in the cabin.

Сorrect volume modeling example

Incorrect volume modeling example

Rules for naming volumes

The volume covering the mesh of the main bone includes the name of that bone. For example: body_vol, turret_vol, engine_vol.

If multiple volumes cover a single bone, numbering is used in the volume names. The naming template is: bonenameN_vol, where N is the serial number. For example: body01_vol, body02_vol, body03_vol.

Reassigning Material ID for polyhedron volume surfaces

In polyhedron volumes for the hull, each polygon must be assigned a Select ID value in the Material IDs parameter within the Polygon properties block. The value must strictly correspond to the following table:

• Front - 1

• Top - 2

• Left - 3

• Right - 4

• Back - 5

• Bottom - 6

The ID parameter determines the virtual armor of the vehicle components: front armor, side armor, rear armor, etc.

Volumes for cabin windows

For vehicles and other units with windows, volumes are created for the glass. They are named window<N>_vol, where <N> is the unique index of the volume.

To add glass destruction animations, the windowed property must be included in the props block of the unit's .def file.

Special-purpose volumes

Volume for ram collision

The ram_vol volume is used to calculate collisions during vehicle ramming. It is a polyhedron with a central convexity to minimize the chance of the vehicle getting stuck when colliding perpendicularly with other objects. Assigning Material ID to surfaces is not required.

Crew volume

The crew_vol volume ensures interaction with the crew inside the vehicle. It is used in models of heavy vehicles with open cabins or transport vehicles with open cargo areas. This volume can be implemented as a primitive geometric shape or as a polyhedron, depending on the model structure. Assigning Material ID to surfaces is not required.

Grenade catcher volume

The sticky_vol volume is responsible for attracting grenades thrown at the vehicle to specific zones. It is used in heavy vehicles with open cabins or transport vehicles with open cargo areas. The volume is formed based on the internal space of the vehicle to increase the likelihood of a grenade entering the vulnerable area.

Fuel tank volume

The fuel_vol volume defines the geometry for interacting with external fuel tanks on vehicles.