mujoco_ros2_control_plugins::ExternalWrenchPlugin Class Reference

Plugin that applies one or more external wrenches (force + torque) to named MuJoCo bodies for configurable durations. More...

#include <external_wrench_plugin.hpp>

Inheritance diagram for mujoco_ros2_control_plugins::ExternalWrenchPlugin:

Collaboration diagram for mujoco_ros2_control_plugins::ExternalWrenchPlugin:

Public Member Functions
bool	init (rclcpp::Node::SharedPtr node, const mjModel *model, mjData *data) override
	Initialize the plugin.
void	pre_step (mjData *data) override
	Called immediately before every simulation step on the physics thread. Default does nothing.
void	cleanup () override
	Cleanup the plugin.
void	publish_markers (visualization_msgs::msg::MarkerArray &markers) const
	Append RViz arrow markers for all currently active wrenches to markers.
Public Member Functions inherited from mujoco_ros2_control_plugins::MuJoCoROS2ControlPluginBase
virtual void	update_read (const mjModel *, mjData *)
	Called once per read() cycle, on the control thread, before the state is handed to ros2_control. Default does nothing.
virtual void	update_write (const mjModel *model, mjData *data)
	Called once per write() cycle, on the control thread, after the hardware interface has staged the controller commands and right before they are sent to the simulation.
virtual void	update (const mjModel *, mjData *)
	Same as update_write(). Default does nothing.
virtual void	on_reset (mjData *)
	Called after a world reset (ResetWorld service or UI reset). Default does nothing.

Detailed Description

Plugin that applies one or more external wrenches (force + torque) to named MuJoCo bodies for configurable durations.

Exposes the ROS 2 service ~/apply_wrench of type mujoco_ros2_control_msgs/srv/ApplyExternalWrench.

The service accepts an array of ExternalWrench messages so that multiple wrenches can be submitted atomically in a single call. All wrenches are validated before any are applied: if any body name is unknown the entire request is rejected.

Each ExternalWrench fields

wrench.header.frame_id - Name of the MuJoCo body (must match MJCF body name) wrench.wrench.force - Linear force [N] expressed in the body (link) frame wrench.wrench.torque - Angular moment [N·m] expressed in the body (link) frame application_point - Point of force application in the body (link) frame (relative to the link frame origin, metres). A zero vector applies at the link frame origin. duration - How long the wrench remains active. A zero duration applies it for one simulation step. ramp_down_duration - Optional linear ramp-down window at the end of duration.

Service response fields

success - false if any body name was not found in the model. message - human-readable status / error description.

Multiple concurrent wrenches on different (or the same) bodies are supported. Each wrench is independent and expires at its own end-time.

Implementation notes

Forces are written into data->xfrc_applied (Cartesian 6D force/torque per body, world frame, applied at the body's inertial CoM xipos). MuJoCo reads this array during mj_step and both applies the force AND renders it as an arrow in the native viewer when "Perturb forces" is enabled.

The service input is expressed in the body's local frame at an arbitrary application point. The plugin converts this to the world-frame wrench at xipos using the standard wrench-transport formula:

F_world = R * F_body τ_world = R * τ_body τ_at_xipos = τ_world + (p_world − xipos) × F_world

where R = data->xmat (body → world rotation) and p_world = data->xpos + R * application_point_body.

pre_step() writes directly into the live xfrc_applied, which holds its value across steps until written again. So at the start of every pre_step() call, the plugin zeroes the xfrc_applied slots it wrote last cycle before re-accumulating the active wrenches, that will release the expired wrenches.

Member Function Documentation

cleanup()

void mujoco_ros2_control_plugins::ExternalWrenchPlugin::cleanup ( )

overridevirtual

Cleanup the plugin.

Implements mujoco_ros2_control_plugins::MuJoCoROS2ControlPluginBase.

init()

bool mujoco_ros2_control_plugins::ExternalWrenchPlugin::init ( rclcpp::Node::SharedPtr  node, const mjModel *  model, mjData *  data  )

overridevirtual

Initialize the plugin.

Parameters

node	Shared pointer to the ROS 2 node for accessing parameters
model	Pointer to the MuJoCo model
data	Pointer to the MuJoCo data

Returns

true if initialization was successful

Note

This method will be called once when the plugin is loaded. It can be used to read parameters, set up publishers/subscribers, etc. The node will be a child of the main mujoco_ros2_control node, so parameters should be namespaced accordingly.

Implements mujoco_ros2_control_plugins::MuJoCoROS2ControlPluginBase.

pre_step()

void mujoco_ros2_control_plugins::ExternalWrenchPlugin::pre_step ( mjData *  )

overridevirtual

Called immediately before every simulation step on the physics thread. Default does nothing.

USE WITH CAUTION.

Parameters

data	Pointer to the live MuJoCo data, can be modified as needed.

Reimplemented from mujoco_ros2_control_plugins::MuJoCoROS2ControlPluginBase.

publish_markers()

void mujoco_ros2_control_plugins::ExternalWrenchPlugin::publish_markers

(

visualization_msgs::msg::MarkerArray &

markers

)

const

Append RViz arrow markers for all currently active wrenches to markers.

This method is additive: existing entries in markers are preserved. It emits nothing when there are no active wrenches, so callers can call it unconditionally and aggregate contributions from multiple plugins before publishing a single MarkerArray.

Marker namespaces: "external_wrench/force" – red arrows, one per active wrench with non-zero force "external_wrench/torque" – cyan arrows, one per active wrench with non-zero torque

Parameters

markers

MarkerArray to append to.

---

The documentation for this class was generated from the following files:

• mujoco_ros2_control/mujoco_ros2_control_plugins/src/external_wrench_plugin.hpp
• mujoco_ros2_control/mujoco_ros2_control_plugins/src/external_wrench_plugin.cpp