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We have seen that our robot is now able to move in the simulation.

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We can drive it using tell your keyboard.

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What we want to do now is to drive it through a Python script because when we are going to move forward,

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our computer vision game is just going to send us command velocities and for command velocity.

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Interpretation into robot motion is very essential.

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For that we are going to create a node and I can write the code right away.

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But what I am going to do is to just create a file here and that is going to be named as driving dot

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by or I should say driving node.

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Okay.

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Kind of.

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But the interesting thing is I am going to get all of its code from Ros Vicky Ros to Subs Publisher

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in in this specific case, we need a publisher in Python.

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Right, a simple publisher and subscriber.

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And we are going to follow a simple structure.

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I'm showing you this because the very first time I learned from this was this last week.

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So coming to the point that we have our package, writing the publisher load, you can download it to

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the minimum publisher or you can get the code from here.

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So if I paste all of the available code here, the risk line library standard messages, string.

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Okay.

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There in basic format, there is a publisher of which is defined in this class and there is a timer

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callback back for that.

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Now the point is it is publishing a string message, but what we would be requiring is a different thing.

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How do I know that?

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Let me show you.

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If we have this terminal here and I bring my robot into that simulation that we want to, I perform

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ROS to topic list to get all of the available topics we have command velocity.

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That is the main topic that we were utilizing.

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So rice top rice to topic, get rice to info, rice to topic in full.

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I think that was the command to geometric message twist and there is no publisher.

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There is one subscriber available which is this robot.

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So geometric message twist.

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This is the main thing coming to the point that in our room what is the node?

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We want geometric message here.

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So if I bring it here and bring the code and decide.

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So we want to make tree message.

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Let me copy pasted geometric message start message and I want twist inside of and this is the message

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type we want.

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You can get information about this topic as well.

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So the topic is not topic, it is command velocity.

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I'm just adjusting the mean publisher of node that is available in rice Vicky and I want it to work

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for my requirements so the message it is going to be communicating is stressed.

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The topic is command velocity and you can call it every second.

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We are going to send not minimal publisher command and let's see just the velocity publisher.

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It is going to be publishing velocities, linear and angular.

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Now in timer callback, you are going to create a message of twist.

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And here comes the reality, which I am going to perform in a moment.

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First, I need to get information about the message type, cross to interface show and the message we

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want to get information about.

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Two.

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Previously we were using the standard message.

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Let's first get information about that standard message.

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And that was standard message string.

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Yes, this was the message that was in our node.

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It says there is only one entry and that is string data entry.

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You can pass the string.

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Okay, now we are going to be using the same no practice to get information about our geometric message

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twist, which is the most common velocity message utilized.

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This contains a linear and an angular vector, so we need to get information about the interface of

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vector.

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Let's get into it.

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Vector does vector contains its own type or is it something else or is a geometric message vector?

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I'm showing you just to give you an idea how you can search about things.

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So it is also a geometric message to geometric message.

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Vector contains X-Y-Z three different values of load for linear and three different values for Angular.

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In our case, what we are going to be only interested in is linear X and angular z.

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So let's start writing about it.

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Message dot linear dot x is equal to 0.5 and message start angular z is equal to 0.3.

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Just to give a rotational angle.

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I will not be giving both at the same time.

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I'm just going to give linear for now and you are going to publish the message and do not log the data.

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We just need we don't need to integrate that as we'll just publish the data and the report is going

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to move in linear X with 0.5 velocity.

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That's it.

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We.

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You need to make this run on our system.

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For that we need to open setup by file in setup by file.

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If we open up the Google Chrome page of Wikipedia for Ros, you can see it entered and we need to add

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this specific line into our setup dot by file of our package so it knows where this executable node

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is sort of path setting.

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So we have this of package of maze board and the name of our node that I want to execute is Driving

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Node.

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What is going to be the name of an executable it will generate?

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I want it to be driving a driving maze board that is that is going to be available to us.

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Now all of the things are set up.

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Let's compile it and see how does it performs.

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Let's open up this as well.

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Now it is this.

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Yes.

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So let's go into our directory of ROS to part planning workspace.

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Now we are inside of our workspace.

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Perform call can be and I will perform allow overriding and the package name is Ms. bought.

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It's me and the scoreboard.

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Have I had it in the same name in the set of the world?

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Nope.

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It would not have appeared.

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You don't have to make such mistakes.

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Things are not going to want rice to run maize board and the name of the node was driving.

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Is it coming?

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Driving mes.

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But I'm pressing dab and it automatically completes.

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Let's see if our robot is moving in linear x or not.

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So you can see a robot is moving in linear x and basically what our achievement is, our node is publishing

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velocity that is controlling the robot.

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We are not driving it through our keyboard.

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Now let's send these velocity, which is some strong angular rotation, very less linear rotation.

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I am going to again perform at the stop this node first and give this up.

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Build it again and hold this robot and bring it back to this specific point.

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And now I am going to.

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Yes, run this node again and see if the robot starts to make anticlockwise rotation or not.

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Yes, it is making anticlockwise rotation because the linear, the angular velocity is positive.

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So it is counterclockwise when it is positive and the linear velocity is also sent.

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If I only send the angular velocity, the robot is just going to stop at 1.2 and rotate.

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But as the linear velocity is, there it is.

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Are they making a circle?

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Sort of.

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So that was it.

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I'm driving.

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Node is ready.

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What else do we need to do?

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We have to look further.

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What are the what are the important nodes we need to build?

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We talk about that and we will build them.