why does this not move my turtle when i do the rosrun command. It doesnt give me an error but it also doesnt move my robot
If I understand correctly, I am setting it to be able to publish values to “/cmd_vel”, I am setting the values I want with the function turtlemovement and then I am telling it to actually publish by command j.turtlemovement(). Shouldnt this move my robot?
Thank you!
Hi, can you please try removing the ‘rospy.spin()’ from ‘move_robot’ and add the following to the end of your script.
rate = rospy.Rate(20)
if name == ‘main’:
while not rospy.is_shutdown():
vel_pub = CmdVelPub()
vel_pub.move_robot(‘forward’)
rate.sleep()
I hope this helps 
The method defined to publish in ‘/cmd/vel’ is never called in the first example
I did this (except changed the ’ to ") and defined a random string to the var “name” before starting the class. the program seems to “run” without error but there is no movement of the robot
in regards to: The method defined to publish in ‘/cmd/vel’ is never called in the first example
how do I do this? I tried adding a function later but it said: “publisher” object is not callable
Please copy/paste the raw code here so we can easily correct it.
With reference to the very first code you shared, the last part of your code should look like this:
# Bring everything under "if name == main"
if __name__ == ‘__main__’:
j = moveturt()
j.turtlemovement()
rospy.spin() # this is optional, since the program publishes only once and does nothing after that
Furthermore, in def turtlemovement(self, ...):
angular_speed = 0, unless you want your turtle to turn as it movesprint("moving"): self.publish_once_in_cmd_vel()
rospy.spin()
#!/usr/bin/env python
import rospy
from geometry_msgs.msg import Twist
rospy.init_node('topic_publisher')
class moveturt():
def __init__(self):
self.turtpublish = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
self.cmd = Twist()
self.rate = rospy.Rate(10) # 10hz
self.publish_once_in_cmd_vel()
rospy.on_shutdown(self.shutdownhook)
def shutdownhook(self):
# works better than the rospy.is_shutdown()
self.ctrl_c = True
def publish_once_in_cmd_vel(self):
"""
This is because publishing in topics sometimes fails the first time you publish.
In continuous publishing systems, this is no big deal, but in systems that publish only
once, it IS very important.
"""
while not self.ctrl_c:
connections = self.turtpublish.get_num_connections()
if connections > 0:
self.turtpublish.publish(self.cmd)
rospy.loginfo("Cmd Published")
break
else:
self.rate.sleep()
def turtlemovement(self, linear_speed=2, angular_speed=2):
self.cmd.linear.x = linear_speed
self.cmd.angular.z = angular_speed
angular_speed = 0,
rospy.loginfo("Moving")
print("moving")
self.publish_once_in_cmd_vel()
if __name__ == '__main__':
j = moveturt()
j.turtlemovement()
rospy.spin() # this is optional since the program publishes only once and does nothing after that
the formating isnt great when I copy and paste so here is teh screen shot for reference:
I get the following error:
Traceback (most recent call last):
File “/home/user/catkin_ws/src/my_turtlebot_topics/scripts/step1bb.py”, line 47, in
j = moveturt()
File “/home/user/catkin_ws/src/my_turtlebot_topics/scripts/step1bb.py”, line 14, in init
self.publish_once_in_cmd_vel()
File “/home/user/catkin_ws/src/my_turtlebot_topics/scripts/step1bb.py”, line 27, in publish_once_in_cmd_vel
while not self.ctrl_c:
AttributeError: ‘moveturt’ object has no attribute ‘ctrl_c’
Ive tried to do things like
def shutdownhook(self, ctrl_c = True):
or
def shutdownhook(self, True):
but still get errors
update: Ive used the following and have been able to get some movement. However, i get the error:
user:~/catkin_ws$ rosrun my_turtlebot_topics step1bbc.py
[INFO] [1621188274.283000, 0.000000]: Moving
moving
Traceback (most recent call last):
File “/home/user/catkin_ws/src/my_turtlebot_topics/scripts/step1bbc.py”, line 33, in
j.turtpublish()
TypeError: ‘Publisher’ object is not callable
To get proper formatting, paste your code between a set of opening and closing tildes (I edited the code for you):
``` → opening tilde
← your code here →
``` → closing tilde
Now to the code. It should be something like:
#!/usr/bin/env python
import rospy
from geometry_msgs.msg import Twist
rospy.init_node('topic_publisher')
class moveturt():
# This is equal to `self.ctrl_c = False` in def __init__(self)
ctrl_c = False
def __init__(self):
self.turtpublish = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
self.cmd = Twist()
self.rate = rospy.Rate(10) # 10hz
self.publish_once_in_cmd_vel()
rospy.on_shutdown(self.shutdownhook)
def shutdownhook(self):
# works better than the rospy.is_shutdown()
self.ctrl_c = True
def publish_once_in_cmd_vel(self):
"""
This is because publishing in topics sometimes fails the first time you publish.
In continuous publishing systems, this is no big deal, but in systems that publish only
once, it IS very important.
"""
while not self.ctrl_c:
connections = self.turtpublish.get_num_connections()
if connections > 0:
self.turtpublish.publish(self.cmd)
rospy.loginfo("Cmd Published")
break
else:
self.rate.sleep()
def turtlemovement(self, linear_speed=0.2, angular_speed=0):
self.cmd.linear.x = linear_speed
self.cmd.angular.z = angular_speed
# angular_speed = 0 # remove this line
rospy.loginfo("Moving")
print("moving")
self.publish_once_in_cmd_vel()
if __name__ == '__main__':
j = moveturt()
j.turtlemovement()
rospy.spin() # this is optional since the program publishes only once and does nothing after that
I recommend that you look at the following resources to build your knowledge of Python and some ROS concepts:
removing rospy.spin() solved my problem
Im not sure why it creates a problem however. Shouldnt it just keep publishing into the same arguments to the /cmd_vel if it is continously running?
Also, I tried
self.ctrl_c = False in def init(self)
on a prior occastion but it gives me the following error:
AttributeError: ‘moveturt’ object has no attribute ‘ctrl_c’
Thank you!!
Very helpful support
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