Real turtlebot robot not responding

ROSDS Support
1

I’m testing out my ‘services’ assignment code (ROS Basics in Python course) on the real turtlebot robot. However, it does not seem to be responding to any ‘/cmd_vel’ commands I publish. Manual movement via joystick works fine, and my code runs perfectly in simulation.

So I checked a few things:

In one terminal window I called the ‘pub’ command to simply rotate in place:

user:~$ rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: -0.2"
publishing and latching message. Press ctrl-C to terminate

And then in another window I printed out the next five ‘/odom’ readings:

user:~$ rostopic echo /odom -n5
header:
  seq: 10094
  stamp:
    secs: 1666318740
    nsecs: 520212015
  frame_id: "odom"
child_frame_id: "base_footprint"
pose:
  pose:
    position:
      x: 0.6423773169517517
      y: 1.0993964672088623
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: -0.9937102198600769
      w: 0.11198201030492783
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: 0.004381328355520964
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---
header:
  seq: 10095
  stamp:
    secs: 1666318740
    nsecs: 552212015
  frame_id: "odom"
child_frame_id: "base_footprint"
pose:
  pose:
    position:
      x: 0.6423773169517517
      y: 1.0993964672088623
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: -0.9937176704406738
      w: 0.11191626638174057
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: -0.004135072231292725
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---
header:
  seq: 10096
  stamp:
    secs: 1666318740
    nsecs: 642212015
  frame_id: "odom"
child_frame_id: "base_footprint"
pose:
  pose:
    position:
      x: 0.6423773169517517
      y: 1.0993964672088623
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: -0.9937560558319092
      w: 0.11157438158988953
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: -0.007645288947969675
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---
header:
  seq: 10097
  stamp:
    secs: 1666318740
    nsecs: 674212015
  frame_id: "odom"
child_frame_id: "base_footprint"
pose:
  pose:
    position:
      x: 0.6423773169517517
      y: 1.0993964672088623
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: -0.9937523007392883
      w: 0.11160825937986374
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: 0.002130866050720215
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---
header:
  seq: 10098
  stamp:
    secs: 1666318740
    nsecs: 756212015
  frame_id: "odom"
child_frame_id: "base_footprint"
pose:
  pose:
    position:
      x: 0.6423773169517517
      y: 1.0993964672088623
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: -0.9937716126441956
      w: 0.1114358976483345
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: -0.00423047598451376
  covariance: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
---

As you can see, the ‘twist.twist.angular.z’ stays effectively at 0.

Any thoughts on what could be the cause of this?

2

Hi,

Let me look into this. Maybe it’s a matter of the robot needing a reset. I will restate your reservations and let you know what I find out.

3

Were you able to assess the issue? I just now tried running my project again and I’m having the same problem.

I did, however, notice that this time when I “manually” publish to the ‘/cmd_vel’ topic, the robot moves just a little in the indicated direction and then stops. For example if I do:

user:~$ rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.1
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0"
publishing and latching message. Press ctrl-C to terminate

it moves a tiny bit forward and then stops. Same with angular velocity commands about z: just a tiny bit of rotation and then stops.

4

I think I now understand what is happening.

You need to publish to cmd_vel with a rate in order for the robot to keep accepting new messages:

rostopic pub -r10 /cmd_vel...

You will need to do the same with your programs

5

Thanks for looking into this. Hmm… this is new, though. I never heard of the “-r10” option. And I don’t believe I have come across it in the ROS Basics coursework so far. My understanding was that the ‘/cmd_vel’ already accepts rate values ([m/s] for linear and [rad/s] for angular), and up to now it has worked just fine without the “-r10”. Certainly in the gazebo simulation environment I have never had to use this option, and my code works fine there. Perhaps this is only something to be used for the real robot?

In any case, I shall give it a try. But what is the equivalent of using “-r10” in code? Typically, you create a publisher object and simply use the ‘.publish()’ method with a ‘Twist()’ object command as its argument. If you could point me to any relevant documentation on this option that would be great.

6

Hi @torino ,

This is just the rate of publishing. If you perform rostopic pub --help you will get that info.

You can set this rate in ROS by setting rate as 10 per second (Hz).
Python: rate = rospy.Rate(10)
C++: ros::Rate rate(10);

That should help you achieve the same behavior as -r10 option in rostopic pub ... command.

Regards,
Girish

7

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