Error trying to rostopic echo the state of the robot

[TONiiV]

Hi,

I launched a kuka robot from the kuka_experimental using

roslaunch kuka_kr16_support load_kr16_2.launch

and then I tried to launch the kuka hw interface

roslaunch kuka_rsi_hw_interface test_hardware_interface.launch

It came up with some warnings, but it seems to connect to the robot successfully.

Then when I try to

rostopic echo /position_trajectory_controller/state

this error poped up:

**Traceback (most recent call last):
  File "/home/ipa325/catkin_ws/src/kuka_experimental/kuka_rsi_simulator/scripts/kuka_rsi_simulator", line 80, in <module>
    rsi_act_pub.publish(msg)
  File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 882, in publish
    self.impl.publish(data)
  File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 1066, in publish
    serialize_message(b, self.seq, message)
  File "/opt/ros/noetic/lib/python3/dist-packages/rospy/msg.py", line 152, in serialize_message
    msg.serialize(b)
  File "/opt/ros/noetic/lib/python3/dist-packages/std_msgs/msg/_String.py", line 56, in serialize
    _x = _x.encode('utf-8')
AttributeError: 'bytes' object has no attribute 'encode'**

It seems to be something wrong with python. The python version is 3.10, ros noetic and ubuntu LTS 20.14. Did anyone come across with the similar problem? And btw is anyone using any Cartesian controller?

Thanks.

[gavanderhoorn]

This doesn't look like an issue with one of the packages here.

/position_trajectory_controller/state is of type control_msgs/JointTrajectoryControllerState, which is a standard message from `control_msgs.

I'm going to close this, as I don't believe this is something we control / cause.

[gavanderhoorn]

Having written that:

The python version is 3.10

ROS Noetic is built against Python 3.8, which is the default version of Python on Ubuntu Focal.

You may want to check what's going on there.

Especially around encoding/decoding of strings and bytearrays there have been a few breaking changes in various Python 3.x versions.

I would not assume there is always (bw) compatibility between Python 3.8 and 3.10.

[gavanderhoorn]

Spoke too soon.

It could be something needs to be updated here:

https://github.com/ros-industrial/kuka_experimental/blob/bd165a723b0547f6daef4203bc8d0ef89188fae0/kuka_rsi_simulator/scripts/kuka_rsi_simulator#L13-L27

I can't test anything right now, but if xml.etree.ElementTree.tostring() returns a bytes instead of a str (or the other way around), rospy.Publisher.publish(..) will probably not be able to deal with that.

[gavanderhoorn]

I'm confused why this would be happening when you rostopic echo /position_trajectory_controller/state btw.

The code mentioned in the trace has nothing to do with that topic.

[TONiiV]

I'm confused as well. Maybe it is because I manually changed the default python version into 3.10 earlier. Right now I can't access the device anymore. Later I may update more informations.

[gavanderhoorn]

Closing due to inactivity.