ROS Topics and Nodes Deep Dive

Ubuntu Version : 20.04
ROS1 Version : NOETIC

This Video makes you understand how nodes communicate under ROS Umbrella .
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[SPeeDKiLL]

when i type in rqt_graph i get the error:

This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

But i used Xlaunch and the turtlesim functions correctly. But when i type in rqt_graph, i get the above error. Do you have maybe an idea why?

[MosesOkpalefe]

Hi, I have been following a few of your videos to really wrap my head around the workings of ROS using turtlesim. I must say your videos are really good and have helped me a lot these last few weeks so a big thank you for your efforts and commitment. I have a question though.

I have spawn two turtles and I am trying to move a specific turtle to a specific location. I have gone through the go2goal tutorial and I understand we need just two parameters and threshold to move the turtle so like in your video, ```linear velocity in x```, ```angular velocity in z``` and the threshold (i.e. when to stop usually a distance).

My challenge is that I am trying to get the position of turtle1 and then use that to calculate the distance, lin_vel.x and ang_vel.z with which turtle2 has to travel. I have written a subscriber function to turtle1 but I want to assign the the x and y positions of turtle1 to a variable that I can use in the move function for turtle2.

I may be struggling due to my beginner level python skills or maybe a poor understanding of how node, topics, subsribers work. Any help will be appreciated. I can show you the code I have written.

[AniketMajetychb]

Hello, everytime I want to run a ros command(rosrun, rostopic, etc.) in a new window, the terminal tells me to install rosbash first(apt install rosbash), for which I have to go to root directory to do so. Everything is working fine, but is there a way around having to use the root deirectory everytime?

[_UtkarshBassi]

I want to write a code in python for turtle to 2 rotation, radius 2, speed 3
Will you please help me

[ShubhamTiwari-ngsp]

how can i use ros2 with arduino mega for serial

[yyjadeja]

Hi Luqman, I have run this

1. # rosrun turtlesim turtlesim_node
qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

2. export QT_QPA_PLATFORM=offscreen
export
export RUNLEVEL=3
source .bashrc

3. # rosrun turtlesim turtlesim_node
QStandardPaths: XDG_RUNTIME_DIR points to non-existing path '/some/directory/you/specify', please create it with 0700 permissions.
[ INFO] [1672405618.508857089]: Starting turtlesim with node name /turtlesim
[ INFO] [1672405618.513468860]: Spawning turtle [turtle1] at x=[5.544445], y=[5.544445],
but haven't got anything on display as you got turtlesim on your screen. how to get visulisation or display

[AhmetOğuzMertoğlu]

rostopic pub /turtle1/cmd_vel geometry_msgs/Twist "linear:
Why can't I get output when I write this? Everything I do is like you do.