Subscribe cmd_vel with Arduino

Question

Hello,

I would want to send PWM signal with an arduino in order to control motors. But, as a beginner, I am not exactly sure of what to do. I need first to publish "cmd_vel". Then I need to write a node in Arduino which subscribe to "cmd_vel", right ?

If so, I am not confident with the code I wrote :

  include "ros.h"

  include "geometry_msgs/Twist.h"
 
 ros::NodeHandle  nh;
 
 void velCallback(const geometry_msgs::Twist& vel) {   
     geometry_msgs::Twist new_vel = vel;   
     // HERE I WANT TO USE vel TO DEFINE PWM  }
 
 void setup() {   
     nh.initNode();  
     ros::Subscriber<geometry_msgs::Twist>  ("cmd_vel", &velCallback); 
}
 
 void loop()
{     
    nh.spinOnce();  
    delay(1); 
}

It is the right way to do ? And is that code correct ?

PS : Sorry but I don't how to properly insert cpp code citation

Regards,

Matt

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Originally posted by mattMGN on ROS Answers with karma: 78 on 2017-04-04

Post score: 0

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Original comments

Comment by NEngelhard on 2017-04-04:
looks ok. How are the motors connected? What kind of motors do you use? Which driver hardware do you use?

Comment by tonybaltovski on 2017-04-04:
Do you have feedback? PWM isn't velocity control.

Comment by mattMGN on 2017-04-05:
I don't want to make feedback control yet. I just want to use cmd_vel, like analogWrite(cmd_vel.linear.x). But currently when I run roscore, compile this arduino script, and run "rosrun rosserial_python serial_node.py /dev/ttyACM0". I just get this message : Connecting to /dev/ttyACM0 at 57600 baud

Comment by mattMGN on 2017-04-05:
Someone know why I am stuck to 'Connecting to /dev/ttyACM0 at 57600 baud' ? And why i can't see my node working with 'rostopic list' ?

Comment by DavidN on 2017-04-05:
Firstly , you should update the question with what you tried and any new error message you have. Secondly, can you check if the serial node is working and sending out data?

Answer 1

I finally find the right syntax to define a publisher

#include "ros.h"

#include "geometry_msgs/Twist.h"

float x; 

ros::NodeHandle nh;

void velCallback(  const geometry_msgs::Twist& vel)
{
     x = vel.linear.x - 1.0; // I CAN USE VEL AS I WANT
}

ros::Subscriber<geometry_msgs::Twist> sub("cmd_vel" , velCallback);

void setup() {
     nh.initNode();
     nh.subscribe(sub);
}

void loop() {
     nh.spinOnce();
     delay(10);
}

Thanks for support

PS : I am still don't knwo how to properly insert cpp code citation

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Originally posted by mattMGN with karma: 78 on 2017-04-06

This answer was ACCEPTED on the original site

Post score: 0

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Original comments

Comment by [email protected] on 2018-07-22:
Hello man, have you figured it out ? I'm having the issue,and would like to know more about