WEBVTT 00:00.230 --> 00:01.910 To simulate our robot in gazebo. 00:02.210 --> 00:05.450 We only need the Urdf model and a launch file. 00:05.570 --> 00:07.250 To start the simulation. 00:07.670 --> 00:14.510 However, the Urdf model we have developed so far is not enough for the simulation as it doesn't contain 00:14.510 --> 00:20.690 all the information needed for Gazebo to simulate the physics and the forces that are acting on the 00:20.690 --> 00:21.380 robot. 00:21.560 --> 00:26.090 So let's add the missing tags inside the Urdf model of our robot. 00:26.180 --> 00:31.940 So in Visual Studio Code, let's go back to the Arduino board description, to the folder, and let's 00:31.940 --> 00:36.020 continue modifying the Arduino Urdf acro model. 00:36.810 --> 00:44.010 First of all, let's notice that each link only has a visual component associated with it that is represented 00:44.010 --> 00:45.360 by the robot mesh. 00:45.360 --> 00:48.930 So here we set for each link a certain robot mesh. 00:49.350 --> 00:55.800 However, while this is enough for RVs to display the robot model, it is not enough for Gazebo to simulate 00:55.800 --> 00:56.220 it. 00:56.520 --> 01:02.970 To achieve this, gazebo needs to know the volume occupied in the space by the link, not just its visualization. 01:03.180 --> 01:09.060 This is indicated with another tag that is called Collision. 01:09.060 --> 01:12.930 And so inside this tag we have the freedom to define the volume. 01:12.930 --> 01:15.720 So the space occupied by a certain link. 01:15.840 --> 01:22.790 For example, we can set that the base link occupy the exact same space as defined in the mesh. 01:22.800 --> 01:29.940 So basically we can copy the content of the visual tag and we can paste it within the collision tag. 01:30.150 --> 01:35.880 In this case, we have decided to use the same mesh both for the visualization and also for the simulation 01:35.880 --> 01:37.030 of the base link. 01:37.240 --> 01:39.400 However, this is not always the case. 01:39.760 --> 01:47.500 A mesh is in general a complex geometry consisting of many surfaces and edges, and it can be computationally 01:47.500 --> 01:53.860 very easy to simulate such geometries, especially when they interact with each other or with other 01:53.860 --> 01:54.820 surfaces. 01:55.420 --> 02:00.880 However, since our robot is very simple and there are very few links and so very few meshes, we can 02:00.880 --> 02:02.890 afford to use the entire mesh. 02:02.890 --> 02:09.100 So the complete mesh also for simulating the robot and so for defining the volume it occupies. 02:09.490 --> 02:15.160 So now let's continue adding the collision tag also to the other links. 02:17.780 --> 02:18.740 And within it. 02:18.740 --> 02:23.720 Let's paste still for all the links, the content of the visual tag. 02:23.720 --> 02:29.960 So for all the links, we are going to use the same mesh that we visualize in our vs also for simulating 02:29.960 --> 02:30.740 the volume. 02:31.550 --> 02:36.470 So let's continue with the forward drive arm. 02:40.260 --> 02:42.060 And then with the horizontal arm. 02:50.180 --> 02:51.830 Then with the closer port. 02:54.320 --> 02:56.180 So let's copy the content. 02:58.100 --> 02:59.240 And then with the gripper. 02:59.240 --> 02:59.840 Right? 03:11.960 --> 03:14.450 And finally the gripper left. 03:16.780 --> 03:18.940 In which you copy its content. 03:20.620 --> 03:25.920 Now let's add another essential piece of information for the simulation of each link. 03:25.920 --> 03:27.540 And this is the inertia. 03:28.260 --> 03:34.560 The inertia of a body, or in this case of a link, is a measure of its resistance to change in the 03:34.560 --> 03:35.250 motion. 03:35.250 --> 03:38.430 And it strongly depends on the mass of the body itself. 03:38.430 --> 03:41.010 And also this mass is distributed. 03:41.280 --> 03:47.220 So starting from the first link from this one, the base link, let's add the inertia matrix of the 03:47.220 --> 03:50.850 body using the tag inertial. 03:51.330 --> 03:57.840 Don't worry if these terms are unfamiliar to you, they are physical parameters of a rigid body that 03:57.840 --> 04:01.650 help understand how it moves under the action of external forces. 04:01.770 --> 04:05.370 So let's add this tag for the base link for the moment. 04:05.370 --> 04:12.210 And this tag will contain a mass and also an inertia. 04:16.310 --> 04:19.040 And let's assign the value of the mass of the body. 04:19.040 --> 04:20.900 So here within the mass tag. 04:21.440 --> 04:25.250 So let's assign it a value of one. 04:26.000 --> 04:28.820 So for the first link, let's assign a value of one. 04:28.820 --> 04:30.800 And for the inertia tag. 04:30.800 --> 04:38.930 So for this one here, we need to assign six attributes that indicate the value of the inertia matrix 04:38.930 --> 04:40.400 of this rigid body. 04:40.700 --> 04:46.610 Once again, we are going to use some default values for this matrix since it is not required in this 04:46.610 --> 04:50.540 course to calculate the correct inertia values of the robot. 04:50.630 --> 04:56.360 And we are going to use these same values for the inertia of all the links that belongs to the robot. 04:57.100 --> 04:59.450 So let's start by adding the property i. 04:59.500 --> 04:59.890 X. 04:59.890 --> 05:00.520 X. 05:01.630 --> 05:06.460 Then i x, y and then i x. 05:06.640 --> 05:07.360 Z. 05:08.530 --> 05:10.330 And let's set this 1 to 1. 05:10.510 --> 05:13.900 So 1.0, then zero. 05:14.590 --> 05:16.390 So 0.0. 05:16.750 --> 05:18.910 And again, 0.0. 05:18.940 --> 05:31.380 Then let's add other properties that are i y y that we set to 1.0 and i y z that we set instead to zero. 05:31.390 --> 05:37.660 And then finally there is the property i, z, z that we set to 1.0. 05:38.710 --> 05:43.840 Just to give you an idea of the meaning of these parameters, they correspond to a matrix with three 05:43.840 --> 05:51.190 rows and three columns called identity matrix because it contains all values equal to zero except for 05:51.190 --> 05:53.230 the main diagonal where it has value. 05:53.230 --> 05:53.740 One. 05:54.010 --> 06:00.190 The logical meaning of this matrix is that the inertia of the link will be the same in all the directions 06:00.190 --> 06:02.290 without any multiplicative factor. 06:03.080 --> 06:03.770 In theory. 06:03.790 --> 06:06.440 Now we should add these same tag inertial. 06:06.440 --> 06:09.740 So basically this is same one for each link. 06:10.010 --> 06:15.860 But since we are assuming that the inertia matrix is the same for all the links, so the only thing 06:15.860 --> 06:18.980 that we would need to change is the inertial tag. 06:18.980 --> 06:22.040 So basically it's the mass value, this one. 06:22.610 --> 06:29.180 To avoid rewriting all the code and in order to adhere to one of the good programming practices, which 06:29.180 --> 06:33.020 is not to repeat the code but use reusable components. 06:33.360 --> 06:39.920 Chakra provides a tool called macro, which can be compared to the functions in the standard programming 06:39.920 --> 06:40.700 languages. 06:40.820 --> 06:46.550 So with a macro, we can define a reusable portion of code simply by using this name. 06:46.550 --> 06:51.890 So we can refer to the full content of the macro simply by calling the name of the macro. 06:52.190 --> 06:57.740 And optionally, we can also pass some parameters to the macro as if it was a function. 06:58.370 --> 07:02.570 So let's create our first macro with the exact format. 07:02.690 --> 07:08.330 So let's use the tag Sakura macro and let's close it. 07:08.480 --> 07:13.820 And like a regular function, we need to assign a name to it, which is the one that we are going to 07:13.820 --> 07:15.190 use in order to call. 07:15.200 --> 07:22.880 So in order to use this macro, so let's assign a name and optionally we can also assign so we can also 07:22.880 --> 07:24.500 pass some parameters. 07:25.520 --> 07:33.290 So this one, in order to configure the behavior of the macro itself, let's call this macro default 07:34.490 --> 07:35.300 inertia. 07:38.000 --> 07:44.870 And the only parameter that it received and that we want to configure is the mass of the link. 07:45.080 --> 07:48.650 Now, inside this function, let's copy. 07:49.820 --> 07:55.820 All the content of the inertia that we have just created for the base link and let's paste it here. 07:55.820 --> 08:02.960 So now we have that the inertial tag, instead of being copied within each link, is within this macro. 08:02.960 --> 08:08.060 So the macro that we called default inertial and here we just need to change. 08:08.060 --> 08:13.340 So in order to use this macro, we need to replace the value of the mass with the mass tag. 08:13.340 --> 08:20.240 So here, instead of using an hardcoded value, we can use the mass. 08:20.240 --> 08:26.510 So basically the value that this macro here received as input, so received as parameter. 08:27.190 --> 08:29.860 Now we can start using this macro here. 08:29.860 --> 08:32.380 So the default inertial in each link. 08:32.380 --> 08:35.620 So whenever we need to define the inertia of the link. 08:36.230 --> 08:42.890 To use these macro, we can use the tag sacrum followed by the name of the macro that we want to use 08:42.920 --> 08:45.950 that we called default. 08:47.470 --> 08:48.220 Inertial. 08:49.980 --> 08:53.820 And to this tag here, we need to pass the mass. 08:53.820 --> 08:55.500 So we need to provide the mass. 08:55.500 --> 08:56.820 And for the first link. 08:56.820 --> 09:00.120 So for the base link, let's use a mass of one. 09:00.600 --> 09:05.300 Now we just need to copy this line and paste it within each link. 09:05.310 --> 09:07.860 So let's start with the base plate. 09:07.980 --> 09:15.190 And here let's set the mass to 0.1, then into the forward drive arm. 09:15.510 --> 09:18.720 And here let's set again the mass to 0.1. 09:19.700 --> 09:21.380 Then the horizontal arm. 09:23.210 --> 09:26.390 And this also uses a mass of 0.1. 09:27.610 --> 09:29.590 Then the close support. 09:29.590 --> 09:31.780 So here and here. 09:31.780 --> 09:35.710 Instead, let's use a mass of 0.05. 09:35.920 --> 09:43.000 And finally, for the gripper right here, let's use a mass of 0.01. 09:43.000 --> 09:45.940 And the same for the gripper left. 09:45.940 --> 09:47.770 So 0.01. 09:48.370 --> 09:51.370 We can save this file with this. 09:51.370 --> 09:56.620 Our RDF model contains all the necessary tags for the simulation of the robot in Gazebo. 09:57.040 --> 10:03.880 In the next lesson, we are going to start the simulation in Gazebo using again the Ros two launch files.