Python vs C++ – see the major difference between running code in the two major languages used by ROS. Let’s go!
Step 1: Create an account and Login to Robot Ignite Academy
On Robot Ignite Academy, you get access to the best online ROS courses and environment. No need to install and set up ROS locally – the only thing you need is a browser!
You’ll now have access to the simulation screen with a Notebook, an Editor, four Shells, and a Simulation Window. We are only using the Editor and Shells for this demo.
Step 2: Create a ROS package and some Python and C++ code
2. 1 Create a package by typing the following command in the shell
cd ~/catkin_ws/src
catkin_create_pkg obiwan rospy roscpp
2.2 Then in the src folder under the obiwan package. Let’s put the two source file obiwancpp.cpp and obiwanpy.py.
#! /usr/bin/env python
import rospy
rospy.init_node("Obiwan")
rate = rospy.Rate(2)
while not rospy.is_shutdown():
print "Help me Obi-Wan Kenobi, you're my only hope"
rate.sleep()
#include <ros/ros.h>
int main(int argc, char** argv) {
ros::init(argc,argv,"ObiWan");
ros::NodeHandle nh;
ros::Rate loop_rate(2);
while(ros::ok())
{
ROS_INFO("Help me Obi-Wan Kenobi, you'are my only hope");
}
return 0;
}
2.3 Type the following command to compile the package
cd ~/catkin_ws
catkin_make
source devel/setup.bash
2.4 After compile, let’s try to run the python script first
rosrun obiwan obiwanpy.py
You should see the output. The script executed without any problem.
2.5 Now try to run the C++ file in the same way. I bet it didn’t run! It turns out, to use the C++ file, you have to uncomment the following part in CMakeLists.txt.
Then compile and run again. You’ll see the output now.
Step 3: Master the Concept – Python vs C++ in ROS
The main difference between using C++ and Python in ROS is that you have to write down comments every time to include all the source files in CMakeLists.txt to compile and generate the executable.
QED 🙂
Extras: Video
Here is a sights and sounds version of the post, in case you prefer to see the action that way!
Further learning
If you are a ROS beginner and would like to learn more about programming ROS, please check one of the courses below, depending on which programming language you’re more familiar with:
In this video we are going to show how to solve the problem of a pioneer 3dx gazebo robot that still moves even after releasing the keyboard, using keyboard twist teleop.
Step 1. Create a project in ROS Development Studio(ROSDS)
ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s create a new project and call it pioneer3dx_do_not_stop.
Step 2. Clone the repository
To reproduce the problem, we have to clone it from the original repository. Create a folder called p3dx under the simulation_ws/src and run the following commands to clone the repository.
cd simulation_ws/src/
mkdir p3dx && cd p3dx
git clone https://github.com/RafBerkvens/ua_ros_p3dx.git
Then you can run the simulation from Simulations->select launch file->gazebo.launch
You can try to control the robot by sending the command to the /p3dx/cmd_vel topic. Then you’ll see the problem. The robot won’t stop even when we stop sending command.
To fix this, we comment out these lines in the /p3dx/p3dx_description/urdf/pioneer3dx.gazebo file
We want to change the controller which support timeout control and we also have to specify transmission property. Several parts have been changed in the repository. You can find the changes in detail here. We also need a parameter file for the controller. Create a file called control.yaml under the /p3dx/p3dx_control/ directory with the following content.
We also have to modify the gazeno.launch file like this to launch the controller.
<launch>
<!-- these are the arguments you can pass this launch file, for example
paused:=true -->
<arg name="paused" default="false" />
<arg name="use_sim_time" default="true" />
<arg name="gui" default="true" />
<arg name="headless" default="false" />
<arg name="debug" default="false" />
<!-- We resume the logic in empty_world.launch, changing only the name of
the world to be launched -->
<include file="$(find gazebo_ros)/launch/empty_world.launch">
<!--<arg name="world_name" value="$(find p3dx_gazebo)/worlds/p3dx.world" />-->
<arg name="debug" value="$(arg debug)" />
<arg name="gui" value="$(arg gui)" />
<arg name="paused" value="$(arg paused)" />
<arg name="use_sim_time" value="$(arg use_sim_time)" />
<arg name="headless" value="$(arg headless)" />
</include>
<group ns="/p3dx">
<!-- Load the URDF into the ROS Parameter Server -->
<param name="robot_description"
command="$(find xacro)/xacro.py --inorder '$(find p3dx_description)/urdf/pioneer3dx.xacro'" />
<!-- Run a python script to the send a service call to gazebo_ros to spawn
a URDF robot -->
<node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model"
respawn="false" output="screen" args="-urdf -param robot_description -model p3dx" />
<rosparam command="load" file="$(find p3dx_control)/config/control.yaml" />
<node name="base_controller_spawner" pkg="controller_manager" type="spawner"
args="--namespace=/p3dx
p3dx_joint_publisher
p3dx_velocity_controller
--shutdown-timeout 3"
output="screen"/>
<!-- ros_control p3rd launch file -->
<!-- <include file="$(find p3dx_control)/launch/control.launch" /> -->
</group>
</launch>
Now you launch the simulation again and execute the following command rosrun teleop_twist_keyboard teleop_twist_keyboard.py cmd_vel:=/p3dx/p3dx_velocity_controller/cmd_vel . You’ll see that the robot stops when you release the key. You can also change the time for timeout in the control.yaml file.
If you are interested in this topic, please check our ROS control 101 course, which explains the ros controller much into detail.
Edit by: Tony Huang
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Step 1. Create a project in ROS Development Studio(ROSDS)
ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s create a new project and call it moveit_qa.
Step 2. Use the moveit package
In this tutorial, we have already preconfigured the fetch robot and moveit package for it. If you want to know how to configure the moveit package, please check our ROS Manipulation in 5 days course. Then we create a file called execute_trajectories.py inside the fetch_moveit_config folder with the following content.
Then we run the script again. The robot should do several movements as we planned.
Want to learn more?
If you want to learn more about the motion planning with moveit package, please check our ROS Manipulation in 5 Days course.
Edit by: Tony Huang
Feedback
Did you like this video? Do you have questions about what is explained? Whatever the case, please leave a comment on the comments section below, so we can interact and learn from each other.
If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.
Still on the series of Markers and how to use them, in the previous Live Class we looked at the Basic RViz Markers and how they are created. Today’s class will delve deeper into other types of Markers available to us in RViz.
We will see:
▸ How to create dynamic BoundingBox Markers
▸ How to add Simple Overlays in ROS RVIZ
Every Tuesday at 18:00 CET/CEST.
This is a LIVE Class on how to develop with ROS. In Live Classes you practice with me at the same time that I explain, with the provided free ROS material.
IMPORTANT: Remember to be on time for the class because at the beginning of the class we will share the code with the attendants.
IMPORTANT 2: in order to start practicing quickly, we are using the ROS Development Studio for doing the practice. You will need a free account to attend the class. Go to http://rds.theconstructsim.com and create an account prior to the class.
Step 1. Create a project in ROS Development Studio(ROSDS)
ROSDS helps you follow our tutorial in a fast pace without dealing without setting up an environment locally. If you haven’t had an account yet, you can create a free account here. Let’s create a new project and call it edit_map_qa.
Step 2. Map generation
In ROS, you can generate a map with SLAM algorithm like gmapping. The map file normally has the .pgm and .yaml foramt where the .pgm is basically an image and .yaml file contains some information like origin, resolution and etc. In this tutorial, I a map is generated using the summit xl robot.
Step 3. Edit map
There are many edit tools available. As a demonstration, we use GIMP on mac to edit the .pgm image. For example, Add a wall in the map.
Step 4. Publish the new map to the map server
Now, you can launch the navigation package again, you’ll see that a new ‘wall’ appears on the map. If you do the path planning again, you should notice that the path is changed due to the wall is blocking the way now.
Want to learn more?
If you are interested in this topic and want to learn more about the navigation stack in ROS and how to use map sever, please check our ROS Navigation in 5 Days Online Course for more information.
Edit by: Tony Huang
Feedback
Did you like this video? Do you have questions about what is explained? Whatever the case, please leave a comment on the comments section below, so we can interact and learn from each other.
If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.
In this video we are going to see how to tune and tweak the parameters required for navigation, using a graphical tool. This tool will enable us to modify parameters on-the-run, allowing us to quickly and painlessly test various parameter settings.
Step1. Create a project in Robot Ignite Academy(RIA)
We have the best online ROS course available in RIA. It helps you learn ROS in the easiest way without setting up ROS environment locally. The only thing you need is a browser! Create an account here and start to browse the trial course for free now! We’ll use the ROS Navigation in 5 days course as an example today. Please go to Unit 0: Guide for ROS Navigation in 5 Days.
Step2. Check the parameter
We use turtlebot 2 as an example. You can use the following command to navigate to the parameter file.
roscd turtlebot_navigation_gazebo
cd param
cat dwa_local_planner_params.yaml
Let’s launch the navigation stack with the following command
If you checked the parameters, you’ll see there are lots of different parameters. How can we tune them? Let’s use a built-in graphical tool called rqt_reconfigure with the following command.
rosrun rqt_reconfigure rqt_reconfigure
Step3. Tune the parameter
For example, the question is about the inflation_radius. You can find it under move_base->global_costmap->inflation_layer.
The best part of this graphical tool is that the change will apply to the simulation immediately, so you can run and tune your navigation stack at the same time. You can also save the parameter to a .yaml file if you click the button on the top left corner.
Want to learn more?
If you want to learn more about the navigation stack and what is the meaning of each parameter, please check our ROS navigation in 5 days course.
Edit by: Tony Huang
Feedback
Did you like this video? Do you have questions about what is explained? Whatever the case, please leave a comment on the comments section below, so we can interact and learn from each other.
If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.
