Lentin Joseph's chefbot Code

Location

• Mastering ROS git

 ~/ros_packages/LentinJoseph/mastering_ros/

Motor Control Python Scripts

 cd ~/ros_packages/LentinJoseph/mastering_ros/chapter_9_codes/chefbot/chefbot_bringup/scripts
 ls
     bkup_working        pid_velocity.py        simple_navig_goals.py
     chefbot_teleop_key  robot_gui.py           twist_to_motors.py
     diff_tf.py          SerialDataGateway.py
     launchpad_node.py   SerialDataGateway.pyc

• pid_velocity.py takes wheel velocity commands and does pid power
• twist_to_motors.py takes navigation twist and converst to motor velocities

Motor Control C++ Source

 cd ~/ros_packages/LentinJoseph/mastering_ros/chapter_9_codes/chefbot_navig_cpp/src
 ls 
     bkup  diff_tf.cpp  twist_to_motor.cpp

• twist_to_motor.cpp takes nav twist and converts to motor velocities

An interesting snippet.

• dx is target linear x speed in m/sec
• dy is target linear y speed in m/sec
• dr is target angular z speed in m/sec
• w wheelbase in m

void TwistToMotors::init_variables()
{
	left = 0;
	right = 0;

	dx = dy = dr =0;

	w = 0.2 ;
	rate = 50;
	timeout_ticks = 2;
}

void TwistToMotors::spinOnce()
{
	right = ( 1.0 * dx ) + (dr * w /2);
	left = ( 1.0 * dx ) - (dr * w /2);

	std_msgs::Float32 left_;
	std_msgs::Float32 right_;

	left_.data = left;
	right_.data = right;

	pub_lmotor.publish(left_);
	pub_rmotor.publish(right_);

	ticks_since_target += 1;

	ros::spinOnce();
}

void TwistToMotors::twistCallback(const geometry_msgs::Twist &msg)
{
	ticks_since_target = 0;
	
	dx = msg.linear.x;
	dy = msg.linear.y;
	dr = msg.angular.z;
}