![]() ![]() Their three-part architecture – goal, feedback, and result – makes ROS actions especially well-suited for long-running tasks. Once the goal succeeds or fails, the action server sends back a response on the result topic. Meanwhile, the client node publishes another request for the action’s result ( step 3). Once that server node acknowledges the goal with a response, it will start publishing feedback, or updates on its progress towards that goal, on a separate topic ( step 2). ROS 2 actions, on the other hand, introduce a completely new interface that integrates the topics and services used in a single type definition.Īt a high level, a client node initiates an action by sending a goal to a server node via a topic ( step 1 in diagram below). Under the hood, ROS 1 actions are built on top of several topics, although they do have to be activated by a service. Services, on the other hand, follow a request-response ( RPC) model – a client node makes a request to a server node, then waits for an asynchronous response. With topics, nodes follow a publisher-subscriber model – a node publishes messages on a topic, while other nodes subscribe to that topic. ![]() ![]() In this tutorial, we’ll discuss how ROS actions work, when to use them, and how to implement a simple action client and server in Python. They combine the best of both worlds, using both open-ended data streams and discrete requests to execute long-running tasks. They can publish an ongoing stream of data via topics, or initiate one-off requests via services.Īctions are a final way for ROS nodes to communicate with each other. There are several different ways that ROS 1 nodes can share information with each other. Millán ♱1 min readPublished August 23, 2022 ![]()
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