Blender Properties Schema

LinkForge stores all robot data as structured Blender custom properties on scene objects. This page is the authoritative reference for every property key, its type, and its default value.

Using LinkForge Data in External Tools

Because all LinkForge data is stored as standard Blender custom properties, any tool that supports glTF 2.0 Custom Properties can read it without needing a URDF parser. This includes game engines (Godot, Unity, Unreal), web renderers (Three.js, Babylon.js), and any custom C++ or Python pipeline.

The workflow is straightforward:

1. Author your robot in Blender using LinkForge as normal.

2. Go to File → Export → glTF 2.0.

3. Under the Data section, enable Custom Properties.

4. The exported .glb file will contain all LinkForge robot data (mass, joints, limits, sensors…) embedded as JSON metadata alongside the 3D geometry.

5. In your target tool, read the metadata using its standard glTF custom properties API.

Important

These property keys are stable. They will not be renamed without a major version bump and a migration note in the CHANGELOG.

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Property Group Keys

Each group is registered on bpy.types.Object under a fixed attribute name. When exported to glTF, this attribute name becomes the JSON metadata key.

glTF Metadata Key	Blender Object Type	Purpose
linkforge	Link Empty	Link identification, physics, inertia
linkforge_joint	Joint Empty (ARROWS)	Joint type, axis, limits, mimic
linkforge_sensor	Sensor Empty	Camera, LIDAR, IMU, GPS, Contact, FT
linkforge_transmission	Transmission Empty	ROS 2 transmission / gear ratios

Note: linkforge_control and linkforge_robot are stored on the Scene, not on individual objects. They are not exported to glTF Custom Properties.

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linkforge — Link Properties

Stored on Link Empty objects (the parent empty of visual and collision meshes).

Identification

Key	Type	Default	Description
is_robot_link	bool	false	true if this object is a robot link
source_name_stored	str	""	Stable robot-model name, immune to Blender .001 suffixing

Physics

Key	Type	Default	Description
mass	float	1.0	Link mass in kilograms
use_auto_inertia	bool	true	When true, inertia is computed from geometry automatically
inertia_ixx	float	1.0	Moment of inertia — X axis (kg·m²)
inertia_iyy	float	1.0	Moment of inertia — Y axis (kg·m²)
inertia_izz	float	1.0	Moment of inertia — Z axis (kg·m²)
inertia_ixy	float	0.0	Cross product of inertia XY (kg·m²)
inertia_ixz	float	0.0	Cross product of inertia XZ (kg·m²)
inertia_iyz	float	0.0	Cross product of inertia YZ (kg·m²)
inertia_origin_xyz	float[3]	[0, 0, 0]	Center-of-mass position offset from link frame (meters)
inertia_origin_rpy	float[3]	[0, 0, 0]	Center-of-mass orientation from link frame (radians, XYZ Euler)

Tip: inertia_ixx / iyy / izz are only read by LinkForge when use_auto_inertia is false.

Collision

Key	Type	Default	Description
collision_type	str	"auto"	Collision shape. One of: "auto", "box", "sphere", "cylinder", "mesh"
collision_quality	float	50.0	Mesh simplification level (1–100%). Only used when collision_type is "mesh"

Material

Key	Type	Default	Description
use_material	bool	false	When true, exports the Blender material color as a URDF <material> tag

Advanced Simulation (Gazebo)

Only exported when use_simulation_props is true.

Key	Type	Default	Description
use_simulation_props	bool	false	Enable Gazebo-specific <gazebo> tag export
gravity	bool	true	Whether this link is affected by gravity
self_collide	bool	false	Whether this link collides with other links in the same robot
mu	float	1.0	Static (Coulomb) friction coefficient
mu2	float	1.0	Dynamic friction coefficient
kp	float	1e12	Contact stiffness (N/m)
kd	float	1.0	Contact damping (N·s/m)

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linkforge_joint — Joint Properties

Stored on Joint Empty objects (ARROWS empties with colored axes).

Identification

Key	Type	Default	Description
is_robot_joint	bool	false	true if this object is a robot joint
source_name_stored	str	""	Stable robot-model name, immune to Blender .001 suffixing

Kinematics

Key	Type	Default	Description
joint_type	str	"revolute"	One of: "revolute", "continuous", "prismatic", "fixed", "floating", "planar"
parent_link	Object pointer	None	Reference to the parent link object
child_link	Object pointer	None	Reference to the child link object
axis	str	"Z"	Motion axis. One of: "X", "Y", "Z", "CUSTOM"
custom_axis_x	float	0.0	Custom axis X component (auto-normalized to unit vector)
custom_axis_y	float	0.0	Custom axis Y component (auto-normalized to unit vector)
custom_axis_z	float	1.0	Custom axis Z component (auto-normalized to unit vector)

Note: custom_axis_* are only read when axis is "CUSTOM".

Limits

Key	Type	Default	Description
use_limits	bool	false	Enable joint position limits
limit_lower	float	-3.14159	Lower position limit — radians for revolute/continuous, meters for prismatic
limit_upper	float	+3.14159	Upper position limit — radians for revolute/continuous, meters for prismatic
limit_effort	float	10.0	Maximum force or torque the actuator can apply (N or N·m)
limit_velocity	float	1.0	Maximum joint velocity (rad/s or m/s)

Dynamics

Key	Type	Default	Description
use_dynamics	bool	false	Include dynamics in the exported URDF
dynamics_damping	float	0.0	Viscous damping — resistance to motion
dynamics_friction	float	0.0	Static friction — resistance to starting motion

Mimic

Key	Type	Default	Description
use_mimic	bool	false	When true, this joint copies another joint’s movement
mimic_joint	Object pointer	None	The joint to copy movement from
mimic_multiplier	float	1.0	Scale factor applied to the mimic joint’s position
mimic_offset	float	0.0	Constant offset added after applying the multiplier

Safety Controller

Key	Type	Default	Description
use_safety_controller	bool	false	Include a safety controller in the exported URDF
safety_soft_lower_limit	float	0.0	Soft lower position bound
safety_soft_upper_limit	float	0.0	Soft upper position bound
safety_k_position	float	0.0	Position gain for the safety controller
safety_k_velocity	float	0.0	Velocity gain for the safety controller

Calibration

Key	Type	Default	Description
use_calibration	bool	false	Include joint calibration data in the exported URDF
use_calibration_rising	bool	false	Include a rising-edge reference position
calibration_rising	float	0.0	Rising-edge reference position (when enabled)
use_calibration_falling	bool	false	Include a falling-edge reference position
calibration_falling	float	0.0	Falling-edge reference position (when enabled)

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linkforge_sensor — Sensor Properties

Stored on Sensor Empty objects.

Identification & Common

Key	Type	Default	Description
is_robot_sensor	bool	false	true if this object is a robot sensor
source_name_stored	str	""	Stable robot-model name
sensor_type	str	"camera"	One of: "camera", "depth_camera", "lidar", "gpu_lidar", "imu", "gps", "contact", "force_torque"
attached_link	Object pointer	None	The link this sensor is physically mounted on
update_rate	float	30.0	Data output frequency (Hz)
always_on	bool	true	Keep the sensor active even when the robot is idle
visualize	bool	false	Render sensor geometry in the simulator viewport
topic_name	str	""	ROS 2 topic name for the sensor data stream

Camera / Depth Camera

Key	Type	Default	Description
camera_horizontal_fov	float	1.047	Horizontal field of view in radians (≈ 60°)
camera_width	int	640	Image width in pixels
camera_height	int	480	Image height in pixels
camera_near_clip	float	0.1	Near clipping distance (meters)
camera_far_clip	float	100.0	Far clipping distance (meters)
camera_format	str	"R8G8B8"	Pixel format. One of: "R8G8B8", "R16G16B16", "L8", "L16", "BAYER_RGGB8", "BAYER_BGGR8"

LIDAR / GPU LIDAR

Key	Type	Default	Description
lidar_horizontal_samples	int	360	Number of horizontal scan rays
lidar_horizontal_min_angle	float	-3.14159	Start angle of the horizontal scan (radians)
lidar_horizontal_max_angle	float	+3.14159	End angle of the horizontal scan (radians)
lidar_vertical_samples	int	1	Number of vertical scan layers (set to 1 for 2D LIDAR)
lidar_vertical_min_angle	float	0.0	Start angle of the vertical scan (radians)
lidar_vertical_max_angle	float	0.0	End angle of the vertical scan (radians)
lidar_range_min	float	0.08	Minimum detectable range (meters)
lidar_range_max	float	10.0	Maximum detectable range (meters)
lidar_range_resolution	float	0.01	Range measurement precision (meters)

Contact Sensor

Key	Type	Default	Description
contact_collision	str	""	Collision element name to monitor. Defaults to <linkname>_collision if empty

Noise Model

Key	Type	Default	Description
use_noise	bool	false	Add a noise model to simulate realistic sensor imprecision
noise_type	str	"gaussian"	Noise distribution. One of: "gaussian", "gaussian_quantized"
noise_mean	float	0.0	Mean of the noise distribution
noise_stddev	float	0.0	Standard deviation of the noise distribution

Gazebo Plugin

Key	Type	Default	Description
use_gazebo_plugin	bool	false	Attach a Gazebo plugin to this sensor
plugin_filename	str	""	Plugin .so filename (e.g. libgazebo_ros_camera.so)

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linkforge_transmission — Transmission Properties

Stored on Transmission Empty objects. Used for ROS 2 <transmission> tags.

Identification

Key	Type	Default	Description
is_robot_transmission	bool	false	true if this object is a robot transmission
source_name_stored	str	""	Stable robot-model name
transmission_type	str	"simple"	One of: "simple", "differential", "four_bar_linkage", "custom"
custom_type	str	""	Custom type identifier (only used when transmission_type is "custom")

Joints & Actuators

Key	Type	Default	Description
joint_name	Object pointer	None	Controlled joint (for "simple" transmissions)
joint1_name	Object pointer	None	First joint (for "differential" transmissions)
joint2_name	Object pointer	None	Second joint (for "differential" transmissions)
hardware_interface	str	"position"	ROS 2 Control interface. One of: "position", "velocity", "effort"
mechanical_reduction	float	1.0	Gear reduction ratio (actuator / joint)
offset	float	0.0	Joint position offset (radians or meters)
use_custom_actuator_name	bool	false	Use a manually specified actuator name
actuator_name	str	""	Actuator name (when use_custom_actuator_name is true)
actuator1_name	str	""	First actuator name (for "differential" transmissions)
actuator2_name	str	""	Second actuator name (for "differential" transmissions)

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Raw ID Properties (Visual & Collision Mesh Children)

These are plain Blender ID properties set directly on child mesh objects using object["key"] = value. They are visible in glTF exports as metadata.

Key	Type	Description
collision_geometry_type	str	Resolved shape: "box", "sphere", "cylinder", or "mesh"
imported_from_source	bool	true if this object was created by importing a URDF
source_geometry_type	str	Original geometry type from the imported URDF
source_name	str	Original object name from the imported URDF