Robot Model Server

Robot Model Server serves the same purpose as robot_state_publisher -- publish robot model and transforms, but has a few distinctive features:

• modular design;
• cumulative inertial parameters;
• visual representations of inertial parameters.

Modules

Repository contains three packages:

• robot_model_server_core — core library with minimal ROS dependencies.

• robot_model_server_ros — ROS 2 wrapper for the core library, deals with ROS topics and parameters.

• robot_model_server_tests — tests and examples.

Cumulative inertial parameters

Core library provides functionality for computation of cumulative inertial parameters: mass, center of mass position, and 3d inertia matrix. Those can be useful in the cases where model represents a robot with no movable joints or their motion can be neglected, e.g., quadcopters.

Visualization of inertial parameters

Robot model server can optionally generate visual representations of inertial parameters and publish them as visualization markers to rviz. This functionality is almost identical to the one provided by default rviz robot model plugin, but gives more control to the user and includes cumulative inertial parameters.

Note that some of the inertias are not specified correctly (red) in the model used for visualization, so the cumulative inertial (blue) is also wrong.

ROS node parameters

• model.description (string) - The original description of the robot in URDF form.
• model.description_file (string) - Read model description from a file, mutually exclusive with model.description
• transform.frequency (double) - The maximum frequency at which non-static transforms (e.g. joint states) will be published to /tf.
• joint_states.ignore_timestamp (bool) - Whether to accept all joint states no matter what the timestamp (true), or to only publish joint state updates if they are newer than the last transform.frequency (false). Defaults to false.
• transform.frame_prefix (string) - An arbitrary prefix to add to the published tf2 frames. Defaults to the empty string.
• visualization.inertia (bool) - Whether to publish inertial visualization markers. When inertia.cumulative is also true, the cumulative inertia marker is published on the same topic. Defaults to false.
• visualization.alpha (double) - Transparency of the inertia visualization markers. Range 0.0 (fully transparent) to 1.0 (fully opaque). Effective when visualization.inertia is true. Defaults to 0.5.
• inertia.cumulative (bool) - Whether to publish cumulative inertial parameters: the center-of-mass transform, the cumulative inertia message, and (when visualization.inertia is also true) the cumulative inertia visualization marker. Defaults to false.
• inertia.tolerance (double) - Tolerance for skipping links with negligible inertial parameters (mass and inertia components all below this value). Effective when either visualization.inertia or inertia.cumulative is true. Defaults to 0.0.

Topics

Published

• robot_description - robot model description in URDF/SDF format as provided by the corresponding parameter.
• tf - the transforms corresponding to the movable joints of the robot.
• tf_static - The transforms corresponding to the static joints of the robot and center of mass position when computation of cumulative inertial parameters is enabled.
• robot_model_server/cumulative_inertia (geometry_msgs::Inertia) - the cumulative inertial parameters (mass, COM, inertia matrix) of the robot assuming all joints fixed at 0. Published on a latched topic when inertia.cumulative is true.

Subscribed

• joint_states (sensor_msgs/msg/JointState) - The joint state updates to the robot poses.