Ackermann Mux

Priority-based multiplexer for Ackermann drive commands. Handles multiple input sources (e.g., joystick, action planning) and selects the highest priority active input to forward to the vehicle control system.

Features

• Priority-based arbitration: Higher priority inputs take precedence over lower priority ones
• Input masking: Enable/disable inputs dynamically via boolean mask topics
• Safety gating: Automatically triggers emergency stop if safety-gated inputs stop sending commands within a configurable timeout
• Emergency fallback: Publishes a safe emergency command when no eligible inputs are available or safety conditions are tripped

Configuration

The node is configured via a YAML file (see config/ackermann_mux_config.yaml). Key parameters:

• safety_threshold: Time in seconds before a safety-gated input triggers emergency (default: 0.5s)
• publish_rate_hz: Rate at which output commands are published (default: 50.0 Hz)
• emergency: Emergency command to publish when no eligible inputs or safety trip occurs
  • steering_angle: Emergency steering angle (default: 0.0)
  • speed: Emergency speed (default: -0.5)
• inputs: List of input sources, each with:
  • topic: ROS topic subscribing to ackermann_msgs/msg/AckermannDriveStamped
  • priority: Priority level (higher number = higher priority)
  • has_mask: Whether this input uses a mask topic (default: false)
  • mask_topic: Topic publishing std_msgs/msg/Bool to enable/disable this input (required if has_mask: true)
  • safety_gating: Whether to enable safety timeout for this input (default: false)

Usage

Launch the node with the default configuration:

ros2 launch ackermann_mux ackermann_mux.launch.yaml

The node publishes multiplexed commands to /ackermann as ackermann_msgs/msg/AckermannDriveStamped.

How It Works

1. Safety Check: If any input with safety_gating: true hasn’t received a command within safety_threshold seconds, the emergency command is published immediately.

2. Arbitration: Among all eligible inputs (have received at least one command and are not masked), the one with the highest priority is selected.

3. Output: The latest command from the selected input is published with an updated timestamp. If no eligible inputs exist, the emergency command is published.

Example Configuration

ackermann_mux:
  ros__parameters:
    safety_threshold: 0.5
    publish_rate_hz: 50.0
    emergency:
      steering_angle: 0.0
      speed: -0.5
    inputs:
      joystick:
        topic: /joystick/ackermann
        priority: 100 # Highest priority
        has_mask: true
        mask_topic: /joystick/is_idle
        safety_gating: true # Will trigger emergency if joystick stops sending commands
      action:
        topic: /action/ackermann
        priority: 10 # Lower priority than joystick
        has_mask: true
        mask_topic: /action/is_idle
        safety_gating: false