URDF → Screw List (ROS 2)

A tiny ROS 2 utility that converts a URDF/Xacro robot model into a Screw List for PoEs-based robot kinematics. It parses the kinematic chain (base → end-effector) and outputs:

• screw_list: twists in $S = [v^\top\ \omega^\top]^\top \in \mathbb{R}^6$ (linear on top, angular below)
• M: the end-effector home pose $^{\mathbf{base}}\xi_{\mathbf{ee}}\in SE(3)$ at zero joint configuration
• Frame options: space or body screws (via use_body_frame)
• joint_limits: per joint limit lower/upper/velocity/effort extracted from URDF
• robot_name: robot name extracted from URDF
• base_link, ee_link, num_joints (DoFs): metadata saved alongside the screw list

Inspired by Modern Robotics (PoEs method), built on urdfdom + kdl_parser + Orocos-KDL.

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Table of Contents

• URDF → Screw List (ROS 2)
  • Table of Contents
  • Features
    • Under development
  • Installation
    • Prerequisites
      • Dependencies from CMakeLists.txt
  • Run Demo
    • OpenArmv10
    • TM5-700

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Features

• URDF/Xacro → Screw list for a chosen chain (base_link → ee_link)
• Twist column order: $S = [v^T \omega^T]^T\in\mathbb{R}^6$ (linear on top, angular below)
• Space or body screws: toggle with use_body_frame
• Home pose representation: emit as (position + quaternion_wxzy) or transformation matrix with home_pose_as_pos_quat
• Plain YAML file output
• One-shot node: runs, writes the file, exits cleanly

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Installation

This is a ROS 2 Humble package.

Prerequisites

• ROS 2 Humble installed & sourced
• C++17 compiler

Dependencies from CMakeLists.txt

• rclcpp
• kdl_parser
• orocos_kdl
• urdf, urdfdom, urdfdom_headers
• eigen3_cmake_module + Eigen3

Build and Install

cd ~/ros2_ws/src
cd ~/ros2_ws && rosdep update && rosdep install --from-paths src --ignore-src -r -y
colcon build --packages-select urdf_to_screw_list && . install/setup.bash

Run Demo

OpenArmv10

The robot_description of openarm_v10 can be downloaded here. Make sure to install it first!!!

ros2 launch urdf_to_screw_list openarm_v10.launch.py \
arm_type:=v10 bimanual:=false \
base_link:=openarm_link0 ee_link:=openarm_hand \
use_body_frame:=true \
home_pose_as_pos_quat:=true \
output_format:=yaml \
output_path:=<your_path>/openarm_v10_body_screws.yaml

Then, you will get openarm_v10_body_screws.yaml:

robot_name: openarm
base_link: openarm_link0
ee_link: openarm_hand
screw_representation: body  # space or body
joint_names: [openarm_joint1, openarm_joint2, openarm_joint3, openarm_joint4, openarm_joint5, openarm_joint6, openarm_joint7]
num_joints: 7
screw_list:
  openarm_joint1: [0.0045000000, 0.0000010000, 0.0000000000, 0.0000000000, 0.0000000000, 1.0000000000]
  openarm_joint2: [0.0000000000, 0.5361000000, 0.0045000000, -1.0000000000, 0.0000000000, 0.0000000000]
  openarm_joint3: [0.0045000000, 0.0000010000, 0.0000000000, 0.0000000000, 0.0000000000, 1.0000000000]
  openarm_joint4: [0.3161000000, 0.0000000000, -0.0000010000, 0.0000000000, 1.0000000000, 0.0000000000]
  openarm_joint5: [0.0045000000, 0.0000010000, 0.0000000000, 0.0000000000, 0.0000000000, 1.0000000000]
  openarm_joint6: [0.0000000000, -0.1001000000, -0.0045000000, 1.0000000000, 0.0000000000, 0.0000000000]
  openarm_joint7: [-0.1001000000, 0.0000000000, 0.0000010000, 0.0000000000, -1.0000000000, 0.0000000000]
joint_limits:
  openarm_joint1: { lower: -1.3962630000, upper: 3.4906590000, velocity: 16.7546660000, effort: 40.0000000000 }
  openarm_joint2: { lower: -1.7453290000, upper: 1.7453290000, velocity: 16.7546660000, effort: 40.0000000000 }
  openarm_joint3: { lower: -1.5707960000, upper: 1.5707960000, velocity: 5.4454260000, effort: 27.0000000000 }
  openarm_joint4: { lower: 0.0000000000, upper: 2.4434610000, velocity: 5.4454260000, effort: 27.0000000000 }
  openarm_joint5: { lower: -1.5707960000, upper: 1.5707960000, velocity: 20.9439460000, effort: 7.0000000000 }
  openarm_joint6: { lower: -0.7853980000, upper: 0.7853980000, velocity: 20.9439460000, effort: 7.0000000000 }
  openarm_joint7: { lower: -1.5707960000, upper: 1.5707960000, velocity: 20.9439460000, effort: 7.0000000000 }
M_position: [0.0000010000, -0.0045000000, 0.6586000000]
M_quaternion_wxyz: [1.0000000000, 0.0000000000, 0.0000000000, 0.0000000000]

TM5-700

The robot_description of tm5-700 can be downloaded here. Make sure to install it first!!!

ros2 launch urdf_to_screw_list tm5_700.launch.py \
base_link:=base ee_link:=flange \
use_body_frame:=true \
home_pose_as_pos_quat:=true \
output_format:=yaml \
output_path:=<your_path>/tm5_700_body_screws.yaml

Then you will get tm5_700_body_screws.yaml:

robot_name: tm5-700
base_link: base
ee_link: flange
screw_representation: body  # space or body
joint_names: [joint_1, joint_2, joint_3, joint_4, joint_5, joint_6]
num_joints: 6
screw_list:
  joint_1: [0.2354500000, 0.0000000000, -0.0000002093, -0.0000000000, 1.0000000000, 0.0000006536]
  joint_2: [0.7465000370, -0.0000002093, -0.0000000000, 0.0000000000, 0.0000006536, -1.0000000000]
  joint_3: [0.4175000370, -0.0000001018, -0.0000000000, 0.0000000000, 0.0000006536, -1.0000000000]
  joint_4: [0.1060000370, 0.0000000000, -0.0000000000, 0.0000000000, 0.0000006536, -1.0000000000]
  joint_5: [0.1131500000, 0.0000000000, -0.0000000000, -0.0000000000, 1.0000000000, 0.0000003268]
  joint_6: [0.0000000000, -0.0000000000, 0.0000000000, -0.0000000000, 0.0000000000, 1.0000000000]
joint_limits:
  joint_1: { lower: -4.7123889804, upper: 4.7123889804, velocity: 3.1415926536, effort: 157.0000000000 }
  joint_2: { lower: -3.1415926536, upper: 3.1415926536, velocity: 3.1415926536, effort: 157.0000000000 }
  joint_3: { lower: -2.7052603406, upper: 2.7052603406, velocity: 3.1415926536, effort: 157.0000000000 }
  joint_4: { lower: -3.1415926536, upper: 3.1415926536, velocity: 3.9269908170, effort: 43.0000000000 }
  joint_5: { lower: -3.1415926536, upper: 3.1415926536, velocity: 3.9269908170, effort: 43.0000000000 }
  joint_6: { lower: -4.7123889804, upper: 4.7123889804, velocity: 3.9269908170, effort: 43.0000000000 }
M_position: [0.0000002863, -0.2354500000, 0.8917000370]
M_quaternion_wxyz: [0.7071070123, 0.7071065501, 0.0000001155, 0.0000001155]

You can then import your own robot descriptions and convert into screw lists!

Acknowledgements

• Robot Math Utils: Some utilities from Robot Math Utils are used.
• Eigen Library: This library heavily relies on the Eigen library for linear algebra operations.

Contact

• Author: Wei-Hsuan Cheng (johnathancheng0125@gmail.com)
• Homepage: wei-hsuan-cheng
• GitHub: wei-hsuan-cheng