Thank you. I am using publish/subscribe interface to send joint commands TO arduino and service/client interface to send joint angles FROM arduino. So, when ever I am publishing new joint commands to arduino, servo_cb callback is called which in turn calls rotate_servo() method with new joint position commands. Now rotate_servo() will move all servos to target angles. The callback() is the service server and its corresponding client is in ros_hw_interface node. So when ever ros hw interface node asks for current joint positions, callback() in arduino will be called and callback() will send the current joint positions of the servos. Hope this clears your doubt. Regards, Sai Krishna.

@@roboticsandroslearning8232 That clears up a lot of things. Thank you so much for your fast respond! I needed to understand this project to advanced my understanding of ROS. Thank you for making the tutorial!

@@roboticsandroslearning8232 I have another question if you don't mind. I have a problem in motor control section. When connect ros to arduio mega using , i get [Error]: Service call failed: service [/read_joint_state] responded with an error: service cannot process request: service handler returned None. I can send command to arduino to rotate the servo, but I'm not getting the feedback, I assumed it has to do with the Error that I got. I can't figure out how to solve this error. I'm using ros melodic by the way. Thanks in advanced!

@@sheenaymu check if your arduino ros_lib have this message "three_dof_planar_manipulator::Floats_array" Else you have to update your ros_lib message. Follow below tutorial wiki.ros.org/rosserial_arduino/Tutorials/Arduino%20IDE%20Setup

@@roboticsandroslearning8232 So I solved part of my problem. I changed 3 things from my previous post. 1. change my arduino board from arduino uno to arduino mega. 2. modify the rosserial_python's SerialClient.py file. 3. Modified your arduino_code.ino's callback() function. From my previous post, I couldn't connect to the arduino board at all. I did a little of research. (1.) I changed my board from arduino uno to arduino mega. (2.) Since I'm using ROS melodic, I replaced the SerialClient.py in /opt/ros/melodic/lib/python2.7/dist-packages/rosserial_python that comes with ROS melodic with ROS kinetic SerialClient.py. By doing these 2 changes, I was able to connect with the arduino board, but I get another problem. I can send command from ROS to all the servos, But I have problem reading from the feedback. When I run your arduino code, arduino_code.ino, I can only read the feedback info from one signal. For example, what you did at 9:00 for all 3 of your servos, I can only do it for only one of my servo. (3.) When I change the arduino_code.ino's callback() function by setting one of the res.res[] = constant, like a number, I can read the feedback info from 2 servos. However when I set all 3 res.res[i] = analogRead(i), respectively, only one servo reads the feedback. I tested all the servos. They all work individually, but when I tried to read from all three servos feedback, only 1 works with your default arduino_code.ino. 2 works when I set one of the res.res[] = const. Right now I'm just tinkering with the Baud rate and understanding the serial_node.py code. Thank you for taking the time to help me out, I read all rosserial_arduino tutorials in roswiki and searched my problems in ros answers, but my problem persist.

Thanks Osama Shaheen. You can get the ik_marker.py code from my git hub. The link to this file is attached below github.com/bandasaikrishna/3-DOF_Manipulator/blob/master/three_dof_planar_manipulator/scripts/ik_marker.py

@@roboticsandroslearning8232 thank you very much

Since you have completed working on 6 dof arm in gazebo using moveit, I think you have already worked on inverse kinematics. Interactive markers can only be used in rviz, not in gazeo and moveit already provides a interactive marker.

@@roboticsandroslearning8232 what i want to implement is like to ...give a coordinate xyz ..and the robot(wid end effector) shud move to that coordinate point using any ik....so what should b my next approach? 2nd how to connect to a real robot. i just want to know it like in steps.

Yes. You can either subscribe to "/joint_states" topic or use "move_group.get_current_joint_values()" to get the current joint position values. Then later you can use "move_group.go(joint_goal, wait=True)" to execute the logged joint positions.

@@roboticsandroslearning8232 Thankyou!

Hi Sohan Anisetty, Do you have the control_manager package installed in your environment? Try installing complete ROS control package using below command and check. For ROS Kinetic: $ sudo apt-get install ros-kinetic-ros-control ros-kinetic-ros-controllers For ROS Lunar: $ sudo apt-get install ros-lunar-ros-control ros-lunar-ros-controllers For ROS Melodic: $ sudo apt-get install ros-melodic-ros-control ros-melodic-ros-controllers If the problem still exists revert back.

To avoid noise interferance

Sorry I didn't get you

Yes you can! Use demo.launch file to run the robot. It provide fake controllers. So in this case you need not use hardware interface node. You can subscribe or publish on fake controllers to control the robot.

Hi Manu Mohan I did not understand your requirement. Why do you want to save the position of servos on Arduino..?

@@roboticsandroslearning8232 I am trying to make a robotic arm where controled by a smart phone and I need to code it easy to . that's why I am ask you that how to store the positions of that servos to Arduino and run the code when I click the specific button on that android app. Can you help me

Hi Houssem Trabelsi, For real robot you can either run real_robot.launch file in three_dof_planar_manipulator_moveit_config package or check_motor_controls.launch file in three_dof_planar_manipulator package. Along with this launch file you also have to run serial_node to communicate with arduino. I have a plan to describe in detail about this manipulator in my blog but it will take some time as I'm currently busy with other things. Most of the details are covered in the video itself. If you still have any query feel free to post it in the comments.

@@roboticsandroslearning8232 after a long period i found the problem you should put the exact dimension of your res array so in Floats_array.srv you change float32 req --- float32[7] res number of joints and every thing it will be ok it works for me

Same error.Any solution???

Have you finished the project bro. I am doing something similar now...

Floats_array.h is a custom message generated by three_dof_planar_manipulator package. You can find this file in srv folder of three_dof_planar_manipulator package. github.com/bandasaikrishna/3-DOF_Manipulator/tree/master/three_dof_planar_manipulator/srv.

@@roboticsandroslearning8232 how add srv file?

Hi @@Geonbbang Sorry, I didn't get your question. Can you be more specific about your question. What exactly you want to know. How to add a custom srv file in you package or how to use Floats_array.h file..?

@@roboticsandroslearning8232 There is no Floats_array.h file in Aduino IDE.

Hi @@Geonbbang , Floats_array.h is not a default ros message. This is generated in the "three_dof_planar_manipulator" package. So this is a custom message. To add custom message headers to arduino library, delete the old "ros_lib" folder(if exists) inside ~/sketchbook/libraries and run below command, Command: rosrun rosserial_arduino make_libraries.py ~/sketchbook/libraries ROS wiki link: wiki.ros.org/rosserial/Tutorials/Adding%20Other%20Messages If you still have any question, feel free to ask.

Go through "Mastering ROS for Robotics Programming" by Lentin Joseph.

Hey did you find a way to do it? I'm getting fixed frame error in rviz can you help?

Follow the steps in below link to add custom messages to arduino lib wiki.ros.org/rosserial_arduino/Tutorials/Adding%20Custom%20Messages

Thanks for your reply! But the problem not solved. Should i make a separate package for arduino code. Including rosserial dependencies

@@dilanjanatu4217 Hey! I am facing the same error where it says no directory.. Did you solve this issue? I'll appreciate any help. Thanks.

Same issue too. Any solution for this?

Hi Houssem Trabelsi, Yes, I faced the same issue when working with 6-DOF arm. So I have stopped reading the joint position values and made a work around for "ROBOTHardwareInterface::read()" in robot_hardware_interface_node.cpp file. Check robot_hardware_interface_node.cpp and arduino_code.ino form my 6-DOF_Manipulator code. 6-DOF_Manipulator: github.com/bandasaikrishna/6-DOF_Manipulator Hope this could solves your issue.

after a long period i found the problem you should put the exact dimension of your res array so in Floats_array.srv you change float32 req --- float32[7] res number of joints and every thing it will be ok it works for me@@roboticsandroslearning8232

Hi @@houssemtrabelsi6090 , I happy that you have solved the error. You fixed the error by setting the length of the array to a fixed length in the srv file. We are setting the length of the array in our arduino code as well ("res.res_length=3;"). So our arduino should work fine too. Have you tried changing length to 7 in arduino code "res.res_length=7;"..? If not, can you try changing the length and let me know the result. Check below links for understanding array messages for rosserial. wiki.ros.org/rosserial/Overview/Limitations wiki.ros.org/rosserial/Overview/Messages

@@roboticsandroslearning8232 I tried but gives me the same proble

Hi @@houssemtrabelsi6090 Thanks for the confirmation.

In command prompt window.

@@roboticsandroslearning8232 Thanks a lot bro. It would be very helpful if you could guide me through which extensions are needed and where they are required. I'm quite new at this and would very much appreciate the help