ActionServer Migration To ROS2

Mar 10, 2025 by ADMIN 31 views

**Migrating ActionServer from ROS1 to ROS2: A Step-by-Step Guide**

Introduction

The Robot Operating System (ROS) has undergone significant changes with the release of ROS2, offering improved performance, security, and scalability. As a result, many ROS1 packages are being migrated to ROS2 to take advantage of these new features. One such package is the ActionServer, which is a crucial component in ROS-based systems. In this article, we will guide you through the process of migrating an ActionServer from ROS1 to ROS2.

Understanding the Basics

Before we dive into the migration process, let's briefly discuss the basics of ActionServer in ROS1 and ROS2.

ROS1 ActionServer

In ROS1, an ActionServer is a node that provides a way to execute actions, which are a sequence of tasks that can be executed in a specific order. The ActionServer is responsible for managing the execution of these actions, including sending feedback and results to the client.

ROS2 ActionServer

In ROS2, the ActionServer is similar to its ROS1 counterpart, but with some significant improvements. The ROS2 ActionServer is designed to be more flexible and scalable, with support for multiple action types and a more robust feedback mechanism.

Migrating the Code

Now that we have a basic understanding of the ActionServer in both ROS1 and ROS2, let's dive into the migration process. We will use the code snippet you provided as a starting point and guide you through the necessary changes.

# ROS1 Code
import rospy
from actionlib import SimpleActionServer
from actionlib_msgs.msg import GoalID
from my_package.msg import MyAction, MyGoal
class MyActionServer:
def init(self):
self.server = SimpleActionServer('my_action_server', MyAction, execute_cb=self.execute_cb, auto_start=False)
self.server.start()
def execute_cb(self, goal):
    # Execute the action
    pass

def cancel_goal(self, goal_id):
    # Cancel the goal
    pass

Step 1: Import the Necessary Modules

The first step in migrating the code is to import the necessary modules. In ROS2, we will use the rclpy library, which is the Python client library for ROS2.

# ROS2 Code
import rclpy
from rclpy.action import ActionServer
from rclpy.node import Node
from my_package.action import MyAction
from my_package.msg import MyGoal

Step 2: Create the ActionServer Node

Next, we need to create the ActionServer node. In ROS2, we will use the Node class from the rclpy library to create a new node.

# ROS2 Code
class MyActionServer(Node):
    def __init__(self):
        super().__init__('my_action_server')
        self.server = ActionServer(self, MyAction, 'my_action_server', self.execute_cb)

Step 3: Define the Execute Callback

The execute callback is a crucial part of the ActionServer, as it is responsible for executing the action. In ROS2, we will define the execute callback as a method of the MyActionServer class.

# ROS2 Code
def execute_cb(self, goal_handle):
    # Execute the action
    pass

Step 4: Define the Cancel Goal Callback

The cancel goal callback is responsible for canceling a goal. In ROS2, we will define the cancel goal callback as a method of the MyActionServer class.

# ROS2 Code
def cancel_goal_cb(self, goal_handle):
    # Cancel the goal
    pass

Step 5: Start the ActionServer

Finally, we need to start the ActionServer. In ROS2, we will use the start method of the ActionServer class to start the server.

# ROS2 Code
def main(self):
    self.server.start()
    rclpy.spin(self)

Putting it all Together

Now that we have gone through the individual steps, let's put it all together. Here is the complete code for the ROS2 ActionServer:

# ROS2 Code
import rclpy
from rclpy.action import ActionServer
from rclpy.node import Node
from my_package.action import MyAction
from my_package.msg import MyGoal
class MyActionServer(Node):
def init(self):
super().init('my_action_server')
self.server = ActionServer(self, MyAction, 'my_action_server', self.execute_cb)
def execute_cb(self, goal_handle):
    # Execute the action
    pass

def cancel_goal_cb(self, goal_handle):
    # Cancel the goal
    pass

def main(self):
    self.server.start()
    rclpy.spin(self)

if name == 'main':
rclpy.init()
node = MyActionServer()
node.main()
rclpy.shutdown()

Conclusion

Migrating an ActionServer from ROS1 to ROS2 requires a good understanding of the basics of ActionServer in both ROS1 and ROS2. By following the steps outlined in this article, you should be able to migrate your ActionServer code from ROS1 to ROS2. Remember to import the necessary modules, create the ActionServer node, define the execute callback, define the cancel goal callback, and start the ActionServer. With these steps, you should be able to successfully migrate your ActionServer code to ROS2.

Additional Resources

For more information on ActionServer in ROS2, please refer to the official ROS2 documentation:

Additionally, you can find more resources on ROS2 migration in the following articles:

ROS1 to ROS2 Migration Guide
ROS2 Migration Tips and Tricks
ROS2 ActionServer Migration Q&A =====================================

Introduction

Migrating an ActionServer from ROS1 to ROS2 can be a complex task, especially for those who are new to ROS2. In this article, we will answer some of the most frequently asked questions about ROS2 ActionServer migration.

Q: What is the main difference between ROS1 and ROS2 ActionServer?

A: The main difference between ROS1 and ROS2 ActionServer is the use of the rclpy library in ROS2. ROS2 uses the rclpy library to create ActionServers, whereas ROS1 uses the actionlib library.

Q: How do I import the necessary modules for ROS2 ActionServer?

A: To import the necessary modules for ROS2 ActionServer, you need to import the rclpy library and the ActionServer class from the rclpy.action module. You also need to import the Node class from the rclpy.node module.

import rclpy
from rclpy.action import ActionServer
from rclpy.node import Node

Q: How do I create an ActionServer node in ROS2?

A: To create an ActionServer node in ROS2, you need to create a new instance of the Node class and pass the name of the node as an argument. You also need to create an instance of the ActionServer class and pass the node instance and the action type as arguments.

class MyActionServer(Node):
    def __init__(self):
        super().__init__('my_action_server')
        self.server = ActionServer(self, MyAction, 'my_action_server', self.execute_cb)

Q: How do I define the execute callback in ROS2 ActionServer?

A: To define the execute callback in ROS2 ActionServer, you need to create a new method in the MyActionServer class and pass the goal handle as an argument. The execute callback is responsible for executing the action.

def execute_cb(self, goal_handle):
    # Execute the action
    pass

Q: How do I define the cancel goal callback in ROS2 ActionServer?

A: To define the cancel goal callback in ROS2 ActionServer, you need to create a new method in the MyActionServer class and pass the goal handle as an argument. The cancel goal callback is responsible for canceling a goal.

def cancel_goal_cb(self, goal_handle):
    # Cancel the goal
    pass

Q: How do I start the ActionServer in ROS2?

A: To start the ActionServer in ROS2, you need to call the start method of the ActionServer instance.

self.server.start()

Q: How do I handle errors in ROS2 ActionServer?

A: To handle errors in ROS2 ActionServer, you need to use the try-except block to catch any exceptions that may occur during the execution of the action.

try:
    # Execute the action
    pass
except Exception as e:
    # Handle the exception
    pass

Q: How do I debug ROS2 ActionServer?

A: To debug ROS2 ActionServer, you can use the rclpy library's built-in debugging tools, such as the rclpy.logging module.

import rclpy.logging
rclpy.logging.get_logger('my_action_server').info('Action executed successfully')

Conclusion

Additional Resources

For more information on ActionServer in ROS2, please refer to the official ROS2 documentation:

Additionally, you can find more resources on ROS2 migration in the following articles: