Force Applicator¶

Overview¶

This package applies external wrenches (forces and torques) to a simulated robot at runtime. It is used for robustness testing and disturbance rejection experiments — e.g., pushing the robot during locomotion to evaluate controller recovery. The applicator supports fixed, random, and periodic disturbance profiles, and interfaces with Gazebo's ApplyLinkWrench service via ros_gz_interfaces.

License¶

The source code is released under a MIT License.

Affiliation: Robomechanics Lab, Carnegie Mellon University

Tested under ROS2 Jazzy on Ubuntu 24.04 with Gazebo Harmonic.

Build¶

colcon build --packages-select force_applicator

Usage¶

Launch the applicator alongside a running Gazebo simulation:

ros2 launch quad_utils force_applicator.py

For single-robot configurations:

ros2 launch quad_utils force_app_single.py

Config¶

config/force_applicator.yaml — wrench magnitudes, disturbance mode, update rate, RNG seed.
config/force_applicator_topics.yaml — topic remappings.

Nodes¶

force_applicator_node¶

Periodically selects a wrench (fixed, random, or periodic) and applies it to the robot trunk link via Gazebo service calls. Also publishes a visualization marker that shows the current applied wrench in RViz.

Subscribed Topics¶

state/ground_truth (quad_msgs/RobotState)

Current robot state, used for position-triggered disturbances.

Published Topics¶

visualization/force_torque_markers (visualization_msgs/MarkerArray)

Arrow markers indicating the magnitude and direction of the applied wrench.
wrench/persistent (ros_gz_interfaces/EntityWrench)

Persistent wrench request sent to the Gazebo bridge.
wrench/clear ([ros_gz_interfaces/Entity])

Clears any persistent wrench.

Key Parameters¶

force_applicator.fixed.force.{x,y,z} (double) — fixed-mode force components in N.
force_applicator.fixed.torque.{x,y,z} (double) — fixed-mode torque components in Nm.
force_applicator.duration.dt (double, default: 0.5) — duration of each applied wrench in seconds.
force_applicator.duration.update_rate (double, default: 100.0) — update rate in Hz.
force_applicator.random.force_mag_{min,max} (double) — per-axis random force magnitude bounds in N.
force_applicator.random.torque_mag_{min,max} (double) — per-axis random torque magnitude bounds in Nm.
force_applicator.periodic.period (double, default: 5.0) — period between disturbances in seconds.
force_applicator.distance.distance_threshold (double, default: 1.0) — trigger distance for position-based disturbances in m.
force_applicator.seed (int, default: 1) — RNG seed for reproducible random disturbances.

Bugs & Feature Requests¶

Please report bugs and request features using the Issue Tracker.