EMCON Gazebo Hardware Interface (emcon_gz_hardware_interface)

A high-performance ros2_control SystemInterface that bridges joint states and commands directly with Gazebo Harmonic using native gz-transport, bypassing the ROS 2 RMW layer entirely.

Why this exists (The Problem)

In standard gz_ros2_control setups, the controller manager runs inside the Gazebo process and communicates over shared memory. While highly efficient for single-robot setups, this architecture presents significant challenges when:

1. Network Isolation: Running complex, custom state estimators or multi-domain networks where simulation traffic (gz-transport) must be strictly isolated from your primary ROS_DOMAIN_ID.
2. Multi-Robot Scaling: Managing fleets of UGV/UAVs where RMW discovery overhead from simulation data congests the network.

The Solution

emcon_gz_hardware_interface acts as a native "data diode" within the ros2_control framework. It functions as a standard SystemInterface in your standalone ROS 2 stack, but uses native gz::transport to subscribe to Gazebo joint states and publish joint commands.

Key Features

• RMW Bypass: Zero ROS 2 topics are used for simulation communication.
• Real-Time Safe: Implements realtime_tools::RealtimeBuffer. The read() method uses atomic pointer dereferencing and never blocks the control loop, even when Gazebo state callbacks fire at high frequencies.
• O(1) Joint Lookup: Optimized hash map lookups ensure low latency regardless of robot complexity.
• Configurable: No hardcoded names or topics. Everything is defined in your URDF.

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Usage

Simply replace your existing Gazebo hardware interface in your URDF with emcon_gz_hardware_interface/EmconGzSystemInterface.

<ros2_control name="emcon_gz" type="system">
  <hardware>
    <plugin>emcon_gz_hardware_interface/EmconGzSystemInterface</plugin>
    
    <!-- Mandatory Parameters -->
    <param name="bot_name">my_robot</param>
    <param name="world_name">my_world</param>
    
    <!-- Optional: Override the Gazebo joint state topic (Defaults to /world/<world_name>/model/<bot_name>/joint_state) -->
    <!-- <param name="joint_state_topic">/custom/topic</param> -->
  </hardware>

  <joint name="joint1">
    <command_interface name="velocity"/>
    <state_interface name="position"/>
    <state_interface name="velocity"/>
  </joint>
</ros2_control>

Supported Command Interfaces

• position (Maps to /model/<bot_name>/joint/<joint_name>/cmd_pos)
• velocity (Maps to /model/<bot_name>/joint/<joint_name>/cmd_vel)
• effort (Maps to /model/<bot_name>/joint/<joint_name>/cmd_force)

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Build Instructions

# Clone into your workspace
cd ~/ros2_ws/src
git clone https://github.com/yenode/emcon_gz_hardware_interface.git

# Install dependencies via rosdep
rosdep update
rosdep install --from-paths . --ignore-src -r -y

# Build
cd ~/ros2_ws
colcon build --packages-select emcon_gz_hardware_interface

Dependencies

• ROS 2 (Tested on Jazzy)
• ros2_control & hardware_interface
• realtime_tools
• Gazebo Harmonic (gz-transport13, gz-msgs10)