Right way to move robots in Gazebo with ROS

asked 2017-02-26 04:13:47 -0500

Entrack
1 ●1 ●1 ●1

Setup:

Pioneer2DX in Gazebo world
Test python script, which rotates robot's right wheel for a second, using ROS service "gazebo/apply_body_wrench":

#!/usr/bin/env python

#ros
import rospy
#msgs
from gazebo_msgs.srv import ApplyBodyWrench
#position
from geometry_msgs.msg import *

apply_wrench = rospy.ServiceProxy("gazebo/apply_body_wrench", ApplyBodyWrench)

wrench = Wrench()
wrench.torque.z = 30.0

apply_wrench("pioneer2dx::right_wheel", "", None, wrench, rospy.Time.from_sec(0), rospy.Duration.from_sec(1.0))

In the result robot moves a little, but the wheel does not change it's relative orientation to the robot. So, the force is created, but the robot rotates not because of the wheel's motion. Nevertheless, when I apply the same torque to the same wheel through Gazebo GUI, it rotates.

So, the questions are:

Why does it happen?
How to make robot move properly? (Maybe I am using the wrong method)

answered 2017-02-27 03:01:30 -0500

Entrack
1 ●1 ●1 ●1

I have solved the problem of moving the robot another way. But anyway maybe it will be helpful to someone else.

I don't know the reason of the issue with wheels, but moving pioneer2dx can be performed using the pluguin. You just add this to your .world file:

<model name='pioneer2dx'>
  <!-- Your model code -->
  <plugin name='differential_drive_controller'
  filename='libgazebo_ros_diff_drive.so'>
  <alwaysOn>true</alwaysOn>
  <updateRate>100</updateRate>
  <leftJoint>left_wheel_hinge</leftJoint>
  <rightJoint>right_wheel_hinge</rightJoint>
  <wheelSeparation>0.39</wheelSeparation>
  <wheelDiameter>0.15</wheelDiameter>
  <torque>5</torque>
  <commandTopic>cmd_vel</commandTopic>
   <odometryTopic>odom</odometryTopic>
   <odometryFrame>odom</odometryFrame>
  <robotBaseFrame>chassis</robotBaseFrame>
  </plugin>
</model>

Once your world is running, you can use this to drive your Pioneer2DX:

publisher = rospy.Publisher('/%s/cmd_vel' % topic, Twist, queue_size=8)
msg = Twist()
msg.linear.x = your_linear_speed
msg.angular.z = your_angular_speed
publisher.publish(msg)

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