How to set the default Yaw angle for the robot in Gazebo launchfile?

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In the launch file, there is a format for setting the XYZ coordinates, like this:

<launch>
    <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
    <arg name="x_pos" default="-1.0"/>
    <arg name="y_pos" default="-6.0"/>
    <arg name="z_pos" default="0.0"/>

But I want to set the robot`s Yaw or Roll, pitch, or Quaternion, How to set them or what the code is, like this:

<arg name="x_pos" default="-1.0"/>

Originally posted by Guapiii on ROS Answers with karma: 3 on 2021-07-01

Post score: 0

score 0 · Accepted Answer · answered Jul 05 '21 at 09:16

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In the launch file

Which launch file are you talking about ? You should include it in your question, or at least tell the node you are trying to launch.

I'm assuming that you want to launch a turtlebot simulation, so it's the node spawn_model from the package gazebo_ros that will handle the initial position. You should have something like this in your launch file :

<node pkg="gazebo_ros" type="spawn_model" name="spawn_urdf"  args="-urdf -model turtlebot3_$(arg model) -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />

Now if you look at all the arguments of the script spawn_model here you will see this :

-x <x in meters> - optional: initial pose, use 0 if left out
-y <y in meters> - optional: initial pose, use 0 if left out
-z <z in meters> - optional: initial pose, use 0 if left out
-R <roll in radians> - optional: initial pose, use 0 if left out
-P <pitch in radians> - optional: initial pose, use 0 if left out
-Y <yaw in radians> - optional: initial pose, use 0 if left out

So you just have to add this in the args of the node spawn_model, after -z $(arg z_pos) for example : -R $(arg ROLL) , with ROLL being the argument name that you should define at the beginning of your launch file.

Edit : You seem to have a little confusion with the arguments of a launch file, the name isn't relevant at all, it's like declaring a variable. The important part is the value you assign to it. You should have a look at the wiki for more explanations.

In your case you have this :

<node pkg="gazebo_ros" type="spawn_model" name="spawn_urdf"  args="-urdf -model turtlebot3_$(arg model) -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />

You give to the node spawn_model a list of arguments, for example you specify the x value by adding -x VALUE where VALUE is set at the beginning of your launch file like this :

<arg name="x_pos" default="-1.0"/>

So if you want to set the roll, pitch or yaw you have to add in the list -R for the roll, -P for the pitch and -Y for the yaw. Like this :

<arg name="roll" default="0.0"/>
<arg name="pitch" default="0.0"/>
<arg name="yaw" default="0.0"/>
<node pkg="gazebo_ros" type="spawn_model" name="spawn_urdf"  args="-urdf -model turtlebot3_$(arg model) -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -R $(arg roll) -P $(arg pitch) -Y $(arg yaw) -param robot_description" />

(you can name the arguments whatever you want, you just need to use them properly)

Originally posted by Delb with karma: 3907 on 2021-07-05

This answer was ACCEPTED on the original site

Post score: 0

Original comments

Comment by Guapiii on 2021-07-07:
I am sorry for not being clear enough in my question. The launch file i am using is ros/melodic/share/turtlebot3_gazebo/turtlebot3_world.launch I used your method to add: <arg name="YAW" default="1.5"/> after <arg name="z_pos" default="0.0"/> But it doesn`t work

Comment by Guapiii on 2021-07-08:
It is true that I do not know enough about the parameters of the launch file. I used your method successfully! Thank you very much for your answer!

How to set the default Yaw angle for the robot in Gazebo launchfile?

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Original comments