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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 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 used to define which axes of the joystick will control our 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 by scaling it and using independent axes to control 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.