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Welcome to your second project.

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This project will deal with creating your own launch files.

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As you saw in the previous lecture.

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Launch files help so that with one command we can automatically run all nodes we are interested in and

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configure them with parameter values.

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In the previous project, a few lectures back we created two nodes, one which publishes the RPM of

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our robot and another which publishes the calculated speed of our robot based on that RPM value and

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our robots wheel radius.

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So now I want you to create a launch file so that with one command you can configure your parameter

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such as the RPM value for the RPM publisher node and a wheel radius parameter for our speed calculator

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node.

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When launching them, then I want to be able to see the speed topic being published to the screen.

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So I also want you to configure the launch file so it runs a ROS two topic echo terminal command to

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print the values coming in from the speed topic.

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So let's break down what this project structure will look like.

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In this project, you will create a launch file that when run in terminal, will run your RPM publisher,

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node and speed calculator node as well as set your wheel radius parameter for the speed calc node to

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utilize.

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This way with one single terminal command utilizing the launch file, we can run multiple nodes and

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configure our parameter.

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As always, remember when attempting this project to make sure you recompile your workspace when you

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make changes, such as adding new launch files and ensure your terminal is source to your workspace.

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With that, pause the video and give yourself about 10 minutes to give this project a go.

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How'd it go?

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I hope you are able to enjoy using just one terminal to launch the entire project rather than having

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three terminal tabs open running different commands.

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Let me show you one of the ways which you could have done it.

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All right with VTS code Open.

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The first thing I will do is create a new launch file.

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I will go ahead and call mine Speed Project launch dot pie.

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And I'll go ahead and copy the contents we made from our previous launch file.

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Since we need to launch the RPM node, we can leave this node as is, but I will go ahead and copy it.

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And add a second node to the launch description list.

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This node will be our speed calc node so we can keep the package name the same, but we will change

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the executable to speed pub py.

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I'll also change the name of this node to speed pub node.

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Great.

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With that, I'm almost done now.

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All I have to do is set my wheel radius parameter.

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I can do this with the parameter argument which I set equal to a list of objects or better known in

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python as dictionaries which contain the name of the parameters and its values.

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In this case, the parameter I want to set is the wheel underscore radius, and I'll just set it 2.5

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to show that the value I set in the launch file will overtake the default value we set in our speed

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node.

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Note that you cannot set a parameter value in the launch file unless you have declared the parameter

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within your code.

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But all right.

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With that, this is all I need to launch the entire Speed Calc project in one command, so I'll go ahead

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and save the file and go to terminal run build task to recompile our workspace.

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Since we created a new launch file.

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All right.

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So that's gone ahead successfully.

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Now, go ahead and open up my terminal, and then I'll go ahead and source my setup file and run this

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new speed project file.

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Here we can see printed to the screen that our two nodes have indeed been launched.

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We can double check this by opening a new terminal tab.

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And running the Ross to Node list command.

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And here we can see our two nodes are running.

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We can even subscribe to our speed topic for a good measure.

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And we see it's running.

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Now let's double check that our parameter for our speed node was properly set, so I can use the RAA

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two parameter list command.

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And here we see under the speed node, the wheel radius parameter, which I can get with raw super ram

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get.

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And here we see the value is 0.5, which is what we set in our launch file, which supersedes the default

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value, which should be 0.125.

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All right.

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With that, congratulations on completing another roster project.

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You've successfully created a launch file that launches multiple nodes and initializes our parameter

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values all within one command in one terminal.

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So it really helps minimize the workload that we have to do manually in other terminals.

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All right.

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Congratulations on completing another raw soup project.

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You have successfully created a launch file that launches multiple nodes, initializes parameter values,

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and can execute various commands all within a single terminal command.