Update example 1.

example_1.md

@@ -10,36 +10,66 @@ First, bringup [Stretch in the empty world simulation](getting_started). Open a
 ```
 python move.py
 ```
-This will drive the robot forward ... 
+This will drive the robot forward ...
 
 
 ```python
 #!/usr/bin/env python
 
+# Every python controller needs these lines
 import rospy
 
+# The Twist message is used to send velocities to the robot.
 from geometry_msgs.msg import Twist
 
 class Move:
 	def __init__(self):
+		# Setup a publisher that will send the velocity commands for the Stretch
+		# This will publish on a topic called "/stretch_diff_drive_controller/cmd_vel"
+		# with a message type Twist.
 		self.pub = rospy.Publisher('/stretch_diff_drive_controller/cmd_vel', Twist, queue_size=1)
 
 	def move_forward(self):
+		# Make a Twist message.  We're going to set all of the elements, since we
+		# can't depend on them defaulting to safe values.
 		command = Twist()
+
+		# A Twist has three linear velocities (in meters per second), along each of the axes.
+		# For Stretch, it will only pay attention to the x velocity, since it can't
+		# directly move in the y direction or the z direction.
 		command.linear.x = 0.1
 		command.linear.y = 0.0
 		command.linear.z = 0.0
+
+		# A Twist also has three rotational velocities (in radians per second).
+		# The Stretch will only respond to rotations around the z (vertical) axis.
 		command.angular.x = 0.0
 		command.angular.y = 0.0
 		command.angular.z = 0.0
+
+		# Publish the Twist commands
 		self.pub.publish(command)
 
 if __name__ == '__main__':
+	# Initialize the node, and call it "move".
 	rospy.init_node('move')
+
+	# Setup Move class to base_motion
 	base_motion = Move()
+
+	# Rate allows us to control the (approximate) rate at which we publish things.
+	# For this example, we want to publish at 10Hz.
 	rate = rospy.Rate(10)
 
+	# This will loop until ROS shuts down the node.  This can be done on the
+	# command line with a ctrl-C, or automatically from roslaunch.
 	while not rospy.is_shutdown():
+		# Run the move_foward function in the Move class
 		base_motion.move_forward()
+
+		# Do an idle wait to control the publish rate.  If we don't control the
+		# rate, the node will publish as fast as it can, and consume all of the
+		# available CPU resources.  This will also add a lot of network traffic,
+		# possibly slowing down other things.
 		rate.sleep()
 ```