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Real Robot Extension — smooth_nav

This document outlines how the smooth_nav system can be extended to run on a physical TurtleBot3 Burger.

Overview

The architecture is designed for a smooth simulation-to-real transition:

  1. smooth_nav_core — No changes needed (pure math, no hardware coupling)
  2. smooth_nav_ros — No changes needed (services are robot-agnostic)
  3. smooth_nav_controller — Minimal changes (tune PID gains for real dynamics)
  4. smooth_nav_bringup — New launch file for real robot

Steps

1. Network Setup

# On the robot (Raspberry Pi)
export ROS_DOMAIN_ID=30

# On the workstation
export ROS_DOMAIN_ID=30

2. Launch on Robot

# SSH into TurtleBot3
ros2 launch turtlebot3_bringup robot.launch.py

3. Launch smooth_nav on Workstation

# Only the service nodes + controller (no Gazebo)
ros2 launch smooth_nav_ros smooth_nav_ros.launch.py
ros2 launch smooth_nav_controller controller.launch.py

4. Tuning

Key parameters to adjust for real hardware (all live-tunable via rqt_reconfigure):

Parameter Sim Value Real Starting Value Notes
max_linear_velocity 0.22 0.15 Start conservative
max_angular_velocity 2.84 1.5 Reduce for stability
look_ahead_distance 0.3 0.4 Increase for sensor lag
adaptive_look_ahead_gain 0.5 0.3 Lower for real-world lag
max_lateral_acceleration 1.0 0.5 Tighter for wheel-slip prevention
goal_deceleration_radius 0.5 0.8 Larger for real inertia
kp_heading 2.0 1.0 Lower gains initially
goal_tolerance 0.05 0.10 Larger for real noise
control_rate 20.0 10.0 Match sensor rate

5. Safety Layer (Already Implemented)

The following safety features are already part of smooth_nav via safety_watchdog_node:

Feature Status Details
Emergency stop (laser proximity) ✅ Implemented Subscribes to /scan, stops when obstacle within safety_distance (default 0.3 m)
Velocity governor ✅ Implemented Clamps /cmd_vel_raw to max_linear_velocity / max_angular_velocity
Command timeout watchdog ✅ Implemented Publishes zero-velocity if no command received within cmd_vel_timeout (default 0.5 s)
Acceleration limiter ✅ Implemented Limits linear acceleration to max_linear_acceleration (default 0.5 m/s²)

For real deployment, tune the safety parameters:

ros2 param set /safety_watchdog safety_distance 0.5        # wider margin
ros2 param set /safety_watchdog max_linear_velocity 0.15   # conservative
ros2 param set /safety_watchdog cmd_vel_timeout 0.3        # faster timeout

What Would Change

Component Change
smooth_nav_controller config Tune PID gains, velocities
smooth_nav_bringup New real_robot.launch.py
smooth_nav_simulation Not used on real robot
URDF Use official turtlebot3_description directly

Testing on Real Hardware

  1. Start with a 1 m straight line at 0.1 m/s
  2. Measure cross-track error with a measuring tape
  3. Gradually increase speed and path complexity
  4. Record rosbag for offline analysis: ./scripts/record_bag.sh