How to get keyboard input to move robot in Python?

asked 2021-08-26 21:30:56 -0600

ModernNoob gravatar image

updated 2021-08-28 12:58:13 -0600

I am working on a simulation with ros and gazebo and I wanted to move a robot with my keystrokes. I had tried to use the keyboard module, but when I ran it with ros run robot_sim move.py it will return an error saying that I must be root to use this module. Is there any other modules/methods that would allow me to get the keystrokes in real time and publish it to a ROS node?

I fixed this issue by stealing someone else's C++ code to get the keystrokes and I use my Python script to subscribe to it:

#include <termios.h>
#include <ros/ros.h>
#include "std_msgs/Int32.h"


int getch() {
    static struct termios oldt, newt;
    tcgetattr( STDIN_FILENO, &oldt);           
    newt = oldt;
    newt.c_lflag &= ~(ICANON);                
    tcsetattr( STDIN_FILENO, TCSANOW, &newt);  
    int ch = getchar();                  
    tcsetattr( STDIN_FILENO, TCSANOW, &oldt); 
    return ch;
}

int main(int argc, char **argv)
{

    ros::init(argc, argv, "keyboard");
    ros::NodeHandle n;

    ros::Publisher pub = n.advertise<std_msgs::Int32>("key_detector", 1000);
    ros::Rate loop_rate(10);


    while (ros::ok())
    {

        std_msgs::Int32 c;
        c.data = getch();  
        pub.publish(c);
        ros::spinOnce();
        loop_rate.sleep();
    }
}
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Comments

Please edit your question to provide a link to the demo/code you downloaded. Most demos support keyboard input control, but you first have to run a "teleop" ros node - the exact name differs for each demo.

You are correct to not use root for this very basic operation. I would be wary of that "keyboard module" you found.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-08-28 09:38:45 -0600 )edit

I'd edited my post with the code I am using right now. It appears that it is working fine after testing it yesterday. I am using mavros and px4 firmware. Now I can get my keyboard input, I am just confuse how to translate that into commands. I know there is an area that I can publish called 

/mavros/setpoint_attitude/cmd_vel

so do I just publish it to that node and it will just run whatever my keyboard is telling it to run?

ModernNoob gravatar image ModernNoob  ( 2021-08-28 13:02:00 -0600 )edit
1

Not sue if I understood well, but I believe you have to dig a bit deeper.

/mavros/setpoint_attitude/cmd_vel is supposed to be the main topic for moving your robot. But when you break it down, you might see some cmd_vel data (x / y / z / angular) related to the keyboard inputs:

Example:

rostopic pub /mobile_base_controller/cmd_vel geometry_msgs/Twist "linear:
  x: 0.5
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0" -r 3

or:

rostopic pub /mobile_base_controller/cmd_vel geometry_msgs/Twist -r 3 -- '[0.5,0.0,0.0]' '[0.0, 0.0, 0.0]'

So, every time a cmd_vel topic is published, it has this data on it, to make the robot move according to its internal programming.
This #q331522 can also help. Again: If I understood well your question.

msantos gravatar image msantos  ( 2021-08-29 06:56:10 -0600 )edit
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