gstavrinos / calc-inertia

Based on a provided URDF (or xacro), it reads all geometries that have a mass inertial tag, and prints a URDF-ready inertia matrix.

calc_inertia_for_urdf.py

Based on a provided URDF (or xacro), it reads all geometries that have a mass inertial tag, and prints a URDF-ready inertia matrix.

Dependencies

• xacro (pip install xacro)
• numpy-stl (pip install numpy-stl)
• pycollada (pip install pycollada)
• urdf_paser_py (pip install urdf-parser-py)

Install with pip install -r requirements.txt

Command line params

• 1: URDF file

Features added in release 2.1

• Support for Collada (.dae) mesh files (in addition to STL)

Features added in release 2.0

• Support for ROS1 AND ROS2. This functionality basically involves looking for mesh files in package:// tags. (If your urdf/xacro only includes file:// tags, there is nothing ROS-related to worry about)
• Support for ALL kind of geometries (mesh, box, sphere, cylinder)
• Xacro integration for files that use arguments or parameters in fields of interest
• Support for links that have inertia but not a visual tag (collisions only)

Example

python calc_inertia_for_urdf.py /home/gstavrinos/urdfs/model.urdf

Output

 Link name: chassis_link_00
 Mass: 48.0
 Scale: [0.015, 0.015, 0.015]
 Mesh: file:///home/gstavrinos/ros2_ws/install/kart_description/share/kart_description/meshes/kart_chassis.stl
---
Calculating inertia...
---

<inertia  ixx="107.96846534714074" ixy="0" ixz="0" iyy="279.5263367708269" iyz="0" izz="346.94143021711494" />

 Link name: steering_wheel_link_00
 Mass: 7.0
 Scale: [0.015, 0.015, 0.015]
 Mesh: file:///home/gstavrinos/ros2_ws/install/kart_description/share/kart_description/meshes/kart_steering_wheel.stl
---
Calculating inertia...
---

<inertia  ixx="1.7008840358588881" ixy="0" ixz="0" iyy="2.939219711456205" iyz="0" izz="3.1101995734940084" />
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calc_inertia.py

⚠️Currently deprecated⚠️

With an object's STL file and mass, calculate its inertia, based on its bounding box, in mass * dimension * scale. The output is URDF-ready.

Dependencies (Compatible with both Python2 and Python3)

• numpy-stl (sudo pip install numpy-stl)

Command line params

• 1: STL file
• 2: Mass (in kg)
• 3: Scale (in case you are scaling your model before use)(= 0.000001 if stl is in mm)

Example

python calc_inertia.py "/home/gstavrinos/meshes/model.stl" 0.025 1