ROS and MORSE tutorial ros

This is an extension of the current tutorial using the ROS as our middleware (instead of raw sockets).

The builder script is almost the same as the one used in the sockets tutorial. The difference is in the interface, which in this case is ROS. You can find it in examples/tutorials/tutorial-1-ros.py.

Configuring ROS

pose.add_stream('ros')
motion.add_stream('ros')

Running the simulation

Run morse with:

morse run examples/tutorials/tutorial-1-ros.py

In another terminal, use the rostopic, rqt_plot and rqt_graph commands to control the robot.

rostopic

First, send a motion command to the robot’s MotionVW actuator:

rostopic pub -1 /atrv/motion geometry_msgs/Twist "{linear: {x: .5}, angular: {z: .5}}"

• pub stands for publish
• -1 will publish 1 message
• /atrv/motion corresponds to the robots’s motion controller topic
• geometry_msgs/Twist is the message’s type
• "{linear: {x: .8}, angular: {z: .5}}" the message in JSON format
  • 0.8 m/s for the linear speed v
  • 0.5 rad/s for the angular speed w

Second, look at its pose:

rostopic echo -n10 /atrv/pose

• echo will subscribe and print
• -n10 will print 10 messages
• /atrv/pose corresponds to the robots’s pose sensor topic

rqt_plot

Once you send a motion command, you can plot the pose in realtime with:

rqt_plot /atrv/pose/pose/position/x,/atrv/pose/pose/position/y /atrv/pose/pose/orientation/z

Note

in former ROS versions, this tool was called rxplot

rqt_grah

This is an alternative to rostopic list showing a collection of nodes and topics.

rospy

From a terminal, start an interactive Python session by typing python3 and type the following code:

import rospy
from geometry_msgs.msg import PoseStamped
from geometry_msgs.msg import Twist

cmd = rospy.Publisher("/atrv/motion", Twist)
motion = Twist()
def callback(msg):
     position = msg.pose.position
     if position.x < 1:
        motion.linear.x = +0.5
     if position.x > 2:
        motion.linear.x = -0.5
     cmd.publish(motion)

rospy.init_node("rostuto1")
rospy.Subscriber("/atrv/pose", PoseStamped, callback)
rospy.spin() # this will block until you press Ctrl+C

You should see the robot move forward then backward after one minute.

Notes

For more information, visit the ROS wiki, where you will find many well written tutorials