ROS 2 Communication Graph

This section documents every node, topic, and message type in the fishing-arm stack, with explicit separation between MuJoCo simulation and Dynamixel hardware modes.

Mode selection recap

A single launch argument — use_sim — drives all structural differences. Application nodes (control, sensors) run in both modes; only their data sources and which ros2_control controllers spawn change.

Concern

Simulation (use_sim:=true)

Hardware (use_sim:=false)

ros2_control host

mujoco_ros2_control/ros2_control_node

controller_manager/ros2_control_node

Hardware plugin (URDF)

mujoco_ros2_control/MujocoSystemInterface

dynamixel_hardware/DynamixelHardware

Extra controllers

fish_effort_controller, tension_sensor_broadcaster

(none)

Disturbance

planning/fish_agent

Real fish / manual load

Tension source param

sensors: source:=sim_fts

sensors: source:=hardware

Sim-only nodes

fish_agent, recorder (when recording)

—

Time

use_sim_time:=true on MuJoCo node

wall clock

Shared closed-loop (both modes)

Regardless of mode, tension control follows the same ROS-level loop:

        flowchart LR
    classDef sense fill:#e3f2fd,stroke:#1565c0,stroke-width:1.5px
    classDef decide fill:#e8f5e9,stroke:#2e7d32,stroke-width:1.5px
    classDef act fill:#fce4ec,stroke:#c62828,stroke-width:1.5px

    DIST["disturbance"]:::act
    ARM["2-DOF arm"]:::act
    LC["load_cell_node"]:::sense
    CTRL["tension ctrl<br/>MONITOR→HOOK→REG"]:::decide
    PTC["pos_traj_controller"]:::act

    DIST --> ARM
    ARM --> LC
    LC -->|/fishing_arm/tension| CTRL
    CTRL -->|/joint_trajectory| PTC --> ARM
    ARM -.->|/joint_states| CTRL

Side-by-side node presence

Node / component

Simulation

Hardware

robot_state_publisher

✓

✓

mujoco_ros2_control / ros2_control_node

✓

—

controller_manager / ros2_control_node

—

✓

joint_state_broadcaster

✓

✓

position_trajectory_controller

✓

✓

fish_effort_controller

✓

✗

tension_sensor_broadcaster

✓

✗

admittance_controller / force_feedback_controller

✓

✓

load_cell_node

✓

✓

fish_agent

✓

✗

recorder

✓ (if record:=true)

optional†

hardware_check

✓ (if flag set)

✓ (if flag set)

† Recorder is sim-oriented (MuJoCo animation) but will still capture plots if launched on hardware.

Controller manager services

Both modes expose the standard ros2_control service API on /controller_manager:

  • ~/list_controllers

  • ~/load_controller / ~/unload_controller

  • ~/switch_controller

Spawner nodes exit after loading; the manager and loaded controllers persist.

TF tree

Published by robot_state_publisher from the processed URDF:

Both modes: base_link → Link_1 → Link_2 → rod_tip_link

Simulation only: base_link → fish_link (via fish_swim prismatic joint)

sensors/load_cell_node uses TF (rod_tip_link ↔ fish_link) in sim to compute line length for the stretch tension model.

Quick topic index

See Topic & Node Reference for the auto-generated full table, or the mode-specific pages: