WEBVTT 00:00.080 --> 00:06.260 Let's experiment a bit more with topics using the total SIM package and the 2D robot simulation. 00:06.260 --> 00:08.600 So let's start by running total sim. 00:08.600 --> 00:17.240 So we use Ros to run total sim and total sim node okay. 00:17.270 --> 00:22.850 So this we have done already in the previous section that's going to start this window. 00:24.260 --> 00:31.910 Let's actually re size here so we can put the window on the side. 00:34.130 --> 00:34.670 Okay. 00:34.700 --> 00:44.750 And I'm going to start here Ros to run total SIM with total Teleop key okay. 00:44.780 --> 00:48.320 So we can you can see we can control the robot here. 00:48.320 --> 00:54.770 And so what we have guessed previously we could only guess that is that this node here is going to communicate 00:54.770 --> 00:55.700 with that one. 00:55.700 --> 01:03.110 Because if we press the keyboard here and the robot is moving, it means that this node must receive 01:03.110 --> 01:04.640 something from that node. 01:04.670 --> 01:05.780 Let's just run. 01:05.790 --> 01:10.560 our cute graph and you can see. 01:10.560 --> 01:19.770 So we have nodes and topics all here that yes the Teleop turtle is you see sending a command velocity 01:19.800 --> 01:20.580 topic here. 01:20.610 --> 01:22.290 Turtle one Cmdvel. 01:22.290 --> 01:23.160 So that's a topic. 01:23.160 --> 01:26.340 And this one is sending data to that topic. 01:26.340 --> 01:28.230 And then this one is a subscriber. 01:28.260 --> 01:32.280 We have more stuff here that we don't need to worry about that for now. 01:32.280 --> 01:35.250 But you can see this is what's interesting for us. 01:35.250 --> 01:37.020 That topic here. 01:37.020 --> 01:39.450 And that's how the two nodes communicate. 01:39.450 --> 01:40.890 So I can close that. 01:40.890 --> 01:44.310 And I can find the same information using the command line. 01:44.310 --> 01:52.260 So Ros2 node list I have my two nodes and then ros2 node info for example with the turtle sim. 01:53.460 --> 02:03.090 And you can see you can see here in the subscribers we have turtle one Cmdvel plus the type okay. 02:03.120 --> 02:05.100 So geometry message. 02:05.130 --> 02:06.030 Twist. 02:06.030 --> 02:09.600 So that's yet another package with messages okay. 02:09.630 --> 02:21.940 And if I do Ross to node info with Teleop turtle, then you can see for that one we have a publisher 02:21.940 --> 02:28.240 that's turtle one Cmdvel with the same data type, so we can find the publisher and the subscriber. 02:28.330 --> 02:34.420 Now I can also do Ross two topic list. 02:34.780 --> 02:37.540 You see we still have the parameter events and the Ross out. 02:37.540 --> 02:41.650 I told you we will always have those and we have three more topics. 02:41.650 --> 02:44.620 But the one that's interesting for us here is that one. 02:44.920 --> 02:51.370 Ross two topic info with Cmdvel. 02:52.300 --> 02:56.830 You see, we have one publisher, one subscriber, so it's the publisher and the subscriber here. 02:56.830 --> 03:05.410 And we also have the type if you want to see the exact data type of that interface, you do Ross two 03:06.250 --> 03:12.760 interface show and you just provide this and you can see here. 03:12.760 --> 03:18.380 So we have this comment, but it's a bit more complex because we have a vector three. 03:18.380 --> 03:19.520 So that's a linear. 03:19.520 --> 03:26.240 And inside this linear field we have x y and z field which are float numbers. 03:26.270 --> 03:26.780 Okay. 03:26.780 --> 03:35.210 So we have linear x linear y linear z and then angular dot x y and z. 03:35.240 --> 03:35.690 Great. 03:35.690 --> 03:38.510 And you can see that we just run those two nodes. 03:38.510 --> 03:42.470 And with our graph you could already get a good idea of what's going on. 03:42.470 --> 03:47.960 And then with the command line tools, we wrote to node and wrote to topic and also wrote to interface. 03:47.960 --> 03:53.810 You can get all the information you need so that you can then create any publisher or subscriber to 03:53.840 --> 03:54.440 that topic. 03:54.470 --> 04:00.200 Okay, you have the name, you have the interface, and you know what's inside the interface. 04:00.380 --> 04:05.720 Just as an additional as a bonus step here, I'm going to also try to publish because now we know what 04:05.720 --> 04:06.230 we have. 04:06.230 --> 04:12.020 So I'm going to publish using Ros2 topic pub. 04:12.110 --> 04:13.790 Let's say I want to publish. 04:13.790 --> 04:16.700 So Dash r I want to publish twice per second. 04:16.850 --> 04:18.230 What's the topic. 04:18.260 --> 04:23.690 The topic is Turtle one Cmdvel. 04:23.690 --> 04:24.980 What is the interface? 04:24.980 --> 04:27.650 The interface is geometry. 04:27.680 --> 04:31.730 Message twist okay, so that's all the information that we found. 04:31.730 --> 04:35.390 And then then what do we need to provide. 04:35.390 --> 04:38.630 So I'm just going to what I'm going to stop that one. 04:38.960 --> 04:49.400 And I'm just going to do this again Ros2 interface show with geometry messages and twist. 04:51.830 --> 04:52.070 Okay. 04:52.100 --> 04:53.660 So this time it's a bit more complex. 04:53.660 --> 04:57.800 So we have the double quotes and then curly brackets. 04:57.800 --> 05:01.880 And we're going to provide for example linear like this. 05:01.880 --> 05:06.980 And we need to put a colon and then another set of curly brackets okay. 05:07.010 --> 05:09.200 Because it's the linear field. 05:09.200 --> 05:12.050 But inside the linear field we have more stuff. 05:12.080 --> 05:17.690 And then I can do x and provide a value for example 1.0. 05:17.690 --> 05:22.340 So here I'm going to send the command so that the turtle can just do a circle. 05:22.340 --> 05:31.260 To do a circle we just need to send a Uh, linear x command and angular z command that are constant. 05:31.350 --> 05:31.560 Okay. 05:31.590 --> 05:33.450 Because here we are in 2D. 05:33.750 --> 05:36.660 So this is a 3D vector okay. 05:36.690 --> 05:42.660 And just to keep things simple here, well x just means that we are going to go forward and backward. 05:42.660 --> 05:47.430 So we only need to go forward and backward and then to make it rotate on itself. 05:47.460 --> 05:47.940 Okay. 05:47.940 --> 05:53.970 We are not going to flip the turtle on the y axis in 3D because what here doesn't exist. 05:53.970 --> 05:56.910 And we cannot also elevate the turtle here. 05:56.910 --> 05:59.580 So the y and z axis don't exist. 05:59.580 --> 06:03.870 And for the angular rotation the x and y rotation also don't exist. 06:03.870 --> 06:06.270 It's only the z rotation. 06:06.300 --> 06:09.330 Okay I'm going to come back to this in the final project. 06:09.360 --> 06:12.600 I'm going to explain also the right hand rule if you don't know that. 06:12.600 --> 06:15.240 So there will be more explanation in the final project. 06:15.240 --> 06:20.310 For now you just have to know that if you want to to move the turtle, you just need to provide the 06:20.310 --> 06:22.290 linear X and the angular Z. 06:22.290 --> 06:28.650 And if you omit some fields, it's okay because the default value is simply going to be zero. 06:28.650 --> 06:32.680 So I can just put x x1 and then after this one. 06:32.680 --> 06:40.360 So I have linear x1 I'm going to put angular and then like that. 06:40.360 --> 06:45.490 So you see it starts to be a bit more complicated as you have a more complex interface. 06:45.490 --> 06:47.860 And I'm going to put Z. 06:48.010 --> 06:55.120 So actually inside the if I change the side here like that okay. 06:55.600 --> 06:58.210 So Z let's say 1.0. 06:58.240 --> 06:58.810 All right. 06:58.810 --> 07:04.540 So make sure you correctly open and close all the curly brackets because it can be a bit tricky. 07:04.540 --> 07:06.850 And with this we should press enter. 07:06.850 --> 07:08.500 And it should work. 07:09.340 --> 07:11.200 You see now the turtle is moving. 07:11.740 --> 07:13.930 It should move in a circle okay. 07:14.050 --> 07:17.950 And if I press ctrl C it's going to stop. 07:17.980 --> 07:18.550 All right. 07:18.550 --> 07:23.530 And so what happened here is that I created a publisher directly from the terminal. 07:23.530 --> 07:28.750 And because I have a subscriber already here, then this node with the subscriber is going to receive 07:28.750 --> 07:30.280 the data from the publisher. 07:30.280 --> 07:32.620 And then here it's going to make the turtle move. 07:32.620 --> 07:35.170 And we can easily see that it's working.