Sim Node

Overview

Sim Node is a ROS node that simulates hardware components of the robot in a virtual environment. It provides:

• Docking station detection
• Battery state simulation
• Charging simulation

The node is designed to work with the Gazebo simulator, listening to model poses and publishing hardware-like topics that mimic the real robot's behavior.

IMPORTANT

The node requires transform information between the robot's base_link and charging_port to accurately detect docking. It also expects a docking station model to be present in the simulation.

Docking Simulation

The Sim Node detects when the robot's charging_port frame is in close proximity to the docking station's charging contacts. When the robot is properly docked:

• The /power/charger_present topic will be true
• The battery will start charging
• A charging voltage will be published on the /power/charge_voltage topic

The node applies configurable offsets to the docking station pose to better represent the actual charging connector position.

Battery Simulation

The battery simulation provides a simplified model of a real battery system:

• Battery discharges at a constant rate when not charging
• Battery charges at a constant rate when docked
• Battery health status is reported based on voltage levels

Topics Published

Topic	Type	Description
/power/charger_present	std_msgs/Bool	Indicates if the robot is properly docked
/power	sensor_msgs/BatteryState	Battery state information including voltage, percentage, and status
/power/charge_voltage	std_msgs/Float32	Voltage provided by the charger when docked

Topics Subscribed

Topic	Type	Description
/model/docking_station/pose	geometry_msgs/Pose	Pose of the docking station in the simulation. See ros_gz_bridge for more details.

Implementation Details

The simulation uses the TF2 library to get the current position of the robot's charging port relative to the map frame. It then calculates the relative position to the docking station to determine if the robot is correctly docked.

Docking is considered successful when the charging port is within 5cm of the docking station's charging contacts. When docked, the battery charging simulation is activated.

The battery simulation logic is simplified:

• If charger is present: Voltage increases at a constant rate until maximum
• If charger is not present: Voltage decreases at a constant rate
• Battery percentage is calculated based on min/max voltage range
• Battery health status (GOOD, DEAD, OVERVOLTAGE) is determined by voltage levels