turtlebot3_patrol_server

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Description

An action server node that autonomously patrols the TurtleBot3 in predefined geometric patterns (square or triangle). The server accepts patrol action goals specifying the shape, side length, and number of iterations. It provides feedback on progress and returns the completion status.

Publishers

cmd_vel (geometry_msgs/Twist)
- Velocity commands for autonomous patrol movements

Subscribers

odom (nav_msgs/Odometry)
- Current robot pose for closed-loop control

Actions

Server

turtlebot3 (turtlebot3_msgs/Patrol)
- Goal:
  - goal.x (float): Pattern type (1.0 = square, 2.0 = triangle)
  - goal.y (float): Side length in meters
  - goal.z (float): Number of iterations
- Feedback:
  - state (string): Current progress (e.g., “line 1”, “line 2”)
- Result:
  - result (string): Completion status message

Parameters

The node uses hardcoded parameters that vary by pattern:

Square Pattern:

Linear velocity: 0.2 m/s
Angular velocity: 13 * (90°/180°) * π / 100.0 rad/s
Turn angle: 90°
Sides: 4

Triangle Pattern:

Linear velocity: 0.2 m/s
Angular velocity: 8 * (120°/180°) * π / 100.0 rad/s
Turn angle: 120°
Sides: 3

Example Usage

Start the patrol server:

ros2 run turtlebot3_example turtlebot3_patrol_server

Send a patrol goal using the client:

ros2 run turtlebot3_example turtlebot3_patrol_client

Or use the action command line:

# Square patrol - 1.0m sides, 2 iterations
ros2 action send_goal /turtlebot3 turtlebot3_msgs/action/Patrol "{goal: {x: 1.0, y: 1.0, z: 2.0}}"

# Triangle patrol - 0.5m sides, 3 iterations
ros2 action send_goal /turtlebot3 turtlebot3_msgs/action/Patrol "{goal: {x: 2.0, y: 0.5, z: 3.0}}"

Behavior

Square Patrol (mode = 1)

Move forward for specified distance
Rotate 90° counterclockwise
Repeat 4 times to complete square
Repeat entire square for specified iterations
Return success result

Triangle Patrol (mode = 2)

Move forward for specified distance
Rotate 120° counterclockwise
Repeat 3 times to complete triangle
Repeat entire triangle for specified iterations
Return success result

Feedback

During execution, the server publishes feedback after completing each side:

“line 1” - First side completed
“line 2” - Second side completed
etc.

Completion

Upon completion:

Final feedback: “square patrol complete!!” or “triangle patrol complete!!”
Result: Same completion message
Server shuts down (triggers rclpy.shutdown())

Control Implementation

Forward Movement

def go_front(position, length):
  - Increment position counter
  - Publish linear.x velocity
  - Continue until position >= length
  - Stop robot

Rotation

def turn(target_angle):
  - Calculate target yaw from current pose
  - Spin until yaw_diff < 0.01 rad
  - Publish angular.z velocity
  - Stop robot

Notes

The server uses ReentrantCallbackGroup to handle concurrent callbacks
Only one goal can be executed at a time (standard action server behavior)
The node automatically shuts down after completing a patrol
Restart the server for subsequent patrol missions
Does not perform obstacle avoidance during patrol
Odometry drift may cause inaccuracies in geometric patterns
Angular velocities are carefully tuned for each pattern’s turn angles