Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags.

How to Write a Generic Teleoperation Node

The Code

   1 #include <ros/ros.h>
   2 #include <turtlesim/Velocity.h>
   3 #include <joy/Joy.h>
   4 
   5 class TeleopTurtle
   6 {
   7 public:
   8   TeleopTurtle();
   9 
  10 private:
  11   void joyCallback(const joy::Joy::ConstPtr& joy);
  12 
  13   ros::NodeHandle nh_;
  14 
  15   int linear_, angular_;
  16   double l_scale_, a_scale_;
  17   ros::Publisher vel_pub_;
  18   ros::Subscriber joy_sub_;
  19 
  20 };
  21 
  22 TeleopTurtle::TeleopTurtle():
  23   linear_(1),
  24   angular_(2),
  25   l_scale_(50.0),
  26   a_scale_(2.0)
  27 {
  28 
  29   nh_.param("axis_linear", linear_, linear_);
  30   nh_.param("axis_angular", angular_, angular_);
  31   nh_.param("scale_angular", a_scale_, a_scale_);
  32   nh_.param("scale_linear", l_scale_, l_scale_);
  33 
  34 
  35   vel_pub_ = nh_.advertise<turtlesim::Velocity>("turtle1/command_velocity", 1);
  36   joy_sub_ = nh_.subscribe<joy::Joy>("joy", 10, &TeleopTurtle::joyCallback, this);
  37 }
  38 
  39 void TeleopTurtle::joyCallback(const joy::Joy::ConstPtr& joy)
  40 {
  41   turtlesim::Velocity vel;
  42   vel.angular = a_scale_*joy->axes[angular_];
  43   vel.linear = l_scale_*joy->axes[linear_];
  44   vel_pub_.publish(vel);
  45 }
  46 
  47 int main(int argc, char** argv)
  48 {
  49   ros::init(argc, argv, "teleop_turtle");
  50   TeleopTurtle teleop_turtle;
  51 
  52   ros::spin();
  53 }

The Code Explained

Now, let's break down the code piece by piece.

Error: No code_block found

• turtlesim/Velocity.h includes the turtle velocity msg, so that we can publish velocity commands to the turtle
• joy/Joy.h includes the joystick msg, so that we can listen to the joy topic

Error: No code_block found Here we create the TeleopTurtle class and the define the joyCallback function that will take a joy msg. We also create a node handle, publisher, and subscriber for later use.

Error: No code_block found Here we initialize some parameters, the linear_ and angular_ variables are use to define which axes of the joystick will control out turtle. We also check the parameter server for new scalar values for driving the turtle.

Error: No code_block found Here we create a publisher that will advertise on the command_velocity topic of the turtle.

Error: No code_block found Here we subscribe to the joystick topic for the input to drive the turtle, we are buffering 10 messages joystick topic.

Error: No code_block found Here we take the data from the joystick and manipulate it, scaling it and using independent axes for controlling the linear and angular velocity of the turtle.

Error: No code_block found Lastly we initialize our ros node, create a teleop_turtle, and spin our node until we get a Crtl-C.