Problem to build on ros2_jazzy - Attribute Error: module 'em' has no attribute 'Interpreter'

[mrRobot62]

Hi, to start - I'm a beginner on ros2.
I have a buch of Dynamical AX12+ servos on my workbench I want to use them for a robot project.

I found your package an tried to install/build it, unfortunately it crashed on cocoon build

Starting >>> dyna_controller_messages
Starting >>> motor_controller
--- stderr: dyna_controller_messages                                                               
CMake Error at /opt/ros/jazzy/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:57 (message):
  execute_process(/home/bernd/venv/ros2/bin/python3 -m rosidl_adapter
  --package-name dyna_controller_messages --arguments-file
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter__arguments__dyna_controller_messages.json
  --output-dir
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter/dyna_controller_messages
  --output-file
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter/dyna_controller_messages.idls)
  returned error code 1:

  AttributeError processing template 'msg.idl.em'

  Traceback (most recent call last):

    File "<frozen runpy>", line 198, in _run_module_as_main
    File "<frozen runpy>", line 88, in _run_code
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/__main__.py", line 19, in <module>
      sys.exit(main())
               ^^^^^^
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/main.py", line 53, in main
      abs_idl_file = convert_to_idl(
                     ^^^^^^^^^^^^^^^
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/__init__.py", line 19, in convert_to_idl
      return convert_msg_to_idl(
             ^^^^^^^^^^^^^^^^^^^
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/msg/__init__.py", line 39, in convert_msg_to_idl
      expand_template('msg.idl.em', data, output_file, encoding='iso-8859-1')
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/resource/__init__.py", line 29, in expand_template
      content = evaluate_template(template_name, data)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/resource/__init__.py", line 65, in evaluate_template
      _interpreter = em.Interpreter(
                     ^^^^^^^^^^^^^^

  AttributeError: module 'em' has no attribute 'Interpreter'

Call Stack (most recent call first):
  /opt/ros/jazzy/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:132 (rosidl_adapt_interfaces)
  CMakeLists.txt:22 (rosidl_generate_interfaces)

Can you assist me?

[2lian]

Hi, thanks for your interest,

You seem to be using ROS2 jazzy under Ubuntu 24.04. I never tested this package with this Jazzy, neither have I ever used Jazzy. So, the error might be due to a change introduced in this new version.

Such an error happening in colcon build is pretty rare. Usually, it happens when ROS2 is not sourced properly before the command. Even more so because the error happens in the dyna_controller_messages which has been generated by ROS2 hence should be as perfect as it can be.

I suspect that you sourced humble and not jazzy while copy-pasting a command of the readme. Here is the command corrected for jazzy that you should use:

source /opt/ros/jazzy/setup.bash
colcon build --symlink-install
. install/setup.bash

(just in case delete build/ install/ log/ , so colcon does not recycle your previous failed build attempts)

If this is not it, and more complicated, I will look into it further.

[mrRobot62]

mhm, I setup a second machine based on Ubuntu 22.04 and installed ros2_humble as described in the ros2-docu.

did several sudo apt updates / upgrades
made rosdep install & update
made the talker / listener test in this works perfectly.
cloned your git
tryied to colcon build as described and got more or less same error message

(ros2) bernd@ros2humbleu2204:~/ros2_ws/dynamixel_hotplug_ros2_python$ source /opt/ros/humble/setup.bash
(ros2) bernd@ros2humbleu2204:~/ros2_ws/dynamixel_hotplug_ros2_python$ colcon build --symlink-install
Starting >>> dyna_controller_messages
Starting >>> motor_controller
--- stderr: dyna_controller_messages                                                               
CMake Error at /opt/ros/humble/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:59 (message):
  execute_process(/home/bernd/venv/ros2/bin/python3 -m rosidl_adapter
  --package-name dyna_controller_messages --arguments-file
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter__arguments__dyna_controller_messages.json
  --output-dir
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter/dyna_controller_messages
  --output-file
  /home/bernd/ros2_ws/dynamixel_hotplug_ros2_python/build/dyna_controller_messages/rosidl_adapter/dyna_controller_messages.idls)
  returned error code 1:

  Traceback (most recent call last):

    File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
      return _run_code(code, main_globals, None,
    File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
      exec(code, run_globals)
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__main__.py", line 19, in <module>
      sys.exit(main())
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/main.py", line 53, in main
      abs_idl_file = convert_to_idl(
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__init__.py", line 18, in convert_to_idl
      from rosidl_adapter.msg import convert_msg_to_idl
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/msg/__init__.py", line 16, in <module>
      from rosidl_adapter.resource import expand_template
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/resource/__init__.py", line 19, in <module>
      import em

  ModuleNotFoundError: No module named 'em'

Call Stack (most recent call first):
  /opt/ros/humble/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:130 (rosidl_adapt_interfaces)
  CMakeLists.txt:22 (rosidl_generate_interfaces)


---
Failed   <<< dyna_controller_messages [0.74s, exited with code 1]
Aborted  <<< motor_controller [1.03s]          

mhm, mhm, btw: the source /opt/ros/humble/setup.bash command is set in my .bashrc file to avoid to forget it to set ;-)

Any more suggestions?
As I said I want to work with my dynamixels because I have a lot of them.
Would be very helpful if you have more ideas and assist me - I know Linus but I'm a ROS-Rookie :-)

[mrRobot62]

ahhh - if fixed it - (or better - I fixed the problem).

Normally I create every time a virtual environment for python. Did the same for my Ubuntu 22.04 installation.
it seems that this was my problem.

I reinstalled every thing again, this time without a venv. Installed rod_humble again and cloned your repo.

tataaaaaa.

No Problem with colcon build :-)

So - no further issue

[mrRobot62]

New Status on ros_jazzy under Ubuntu 24.04 - compiling possible

ok, on my PI5 machine with Ubuntu 24.04 - I'm now able to compile too - but I had to to some additional steps

1. remove my installed venv environment
2. reinstalled ros2 completly new for jazzy
3. cloned your git again and tried to compile
4. known failure ModuleNotFoundError: No module named 'em'
5. do some research and found this: [https://github.com/My ROS system is ROS2 foxy, but there was an error compiling ROS bridge on Ubuntu 20. I don't know how to solve it carla-simulator/ros-bridge#712
6. try to install pip install empy==3.3.4 - not possible under Ubunto 24.04 (=> error: externally-managed-environment)
7. install pipx (sudo apt install pipx)
8. pipx install colcon-common-extensions --include-deps
9. pipx install empy==3.3.4
10. pipx ensurepath

for saftey issues - removed your git and cloned it again

go into folder
set source /opt/ros/jazzy/setup.bash
colcon build ---symlink-install

and got this :-)

colcon build --symlink-install
Starting >>> dyna_controller_messages
Starting >>> motor_controller
Finished <<< motor_controller [3.47s]                                        
Finished <<< dyna_controller_messages [11.0s]        

(Ignore error ....not port/path may not exist - I had not U2D2 plugged in for this test)

bernd@ros-pi:~/ros2_ws/dynamixel_hotplug_ros2_python$ ros2 launch src/motor_controller/launch/multi_port_launch.py
[INFO] [launch]: All log files can be found below /home/bernd/.ros/log/2025-01-12-17-58-47-759287-ros-pi-6124
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [u2d2_dyna_controller-1]: process started with pid [6128]
[INFO] [u2d2_dyna_controller-2]: process started with pid [6129]
[INFO] [u2d2_dyna_controller-3]: process started with pid [6130]
[INFO] [u2d2_dyna_controller-4]: process started with pid [6131]
[INFO] [u2d2_dyna_controller-5]: process started with pid [6132]
[INFO] [angle_remapper-6]: process started with pid [6133]
[u2d2_dyna_controller-2] [WARN] [1736701129.239258187] [Dyna_port_1]: Port port_1 [path: /dev/ttyUSB1, proto: 2.00]: Serial error 2 on opening, port/path may not exist
[u2d2_dyna_controller-2] [WARN] [1736701129.241391085] [Dyna_port_1]: Port port_1: failed to open. Silently retrying every 1 s.
[u2d2_dyna_controller-1] [WARN] [1736701129.243769498] [Dyna_port_0]: Port port_0 [path: /dev/ttyUSB0, proto: 2.00]: Serial error 2 on opening, port/path may not exist
...

Tataaaaa :-)

[mrRobot62]

Sorry for spamming ;-)

As you know I want to Use AX12 servos. As I understand your source code, in launch_settings.py

MotorSeries = "X_SERIES"
# The motor series changes the adresses used on the serial port
# Only the Xseries addresses are usable, update `motor_address_table` in multi_controller.py for another motor
# 'X_SERIES'  # X330 (5.0 V recommended), X430, X540, 2X430
# 'MX_SERIES'    # MX series with 2.0 firmware update.
# 'PRO_SERIES'   # H54, H42, M54, M42, L54, L42
# 'PRO_A_SERIES' # PRO series with (A) firmware update.
# 'P_SERIES'     # PH54, PH42, PM54
# 'XL320'        # [WARNING] Operating Voltage : 7.4V

you set MotorSeries, but I don't know what is the right name for AX-Servos :-/ - Do you know?
AX12 Servos are running with protocols 1.0, in multi protocol_handler.py. Not sure, maybe I have to adapt the baud rate as well.

However the missing link ist the correct name for MotorSeries.

[2lian]

Good job making colcon work on a venv, usually it is not advised to use a venv with ROS2. If you keep having issues with ROS in the future, it could stem from this. For developing a bigger package than this one, I find that ros2 dependencies and packages management are a bit rough (especially Foxy), I hope Jazzy improved on that.

About the dynamixel AX12+, the package was made with the X series in mind as it is the most popular (and only one I have). To add support for an AX series, you need to provide the corresponding address table here:

dynamixel_hotplug_ros2_python/src/motor_controller/motor_controller/python_package_include/multi_controller.py

Line 39 in 52f2a30

motor_address_table = {

(the "BAUDRATE" entry is not used, so don't worry about it). Then you can use "AX_SERIES" for the ros parameter.

Those already provided address come from the dynamixel SDK. Sadly your AX address table is not provided by the SDK, so you will have to make it yourself based on the docs: https://emanual.robotis.com/docs/en/dxl/ax/ax-12a/#control-table-of-eeprom-area.

The current code requires all entries that are used by the X_series:

    'X_SERIES': {
        "ADDR_TORQUE_ENABLE": 64,

        "ADDR_LED_RED": 65,
        "LEN_LED_RED": 1,

        "ADDR_GOAL_POSITION": 116,
        "LEN_GOAL_POSITION": 4,

        "ADDR_PRESENT_POSITION": 132,
        "LEN_PRESENT_POSITION": 4,

        "ADDR_MAX_VELOCITY": 112,
        "LEN_MAX_VELOCITY": 4,

        "DXL_MINIMUM_POSITION_VALUE": 0,
        "DXL_MAXIMUM_POSITION_VALUE": 4095,
    }

I think those are the corresponding addresses:

motor_address_table = {
...
    'AX_SERIES': {
        "ADDR_TORQUE_ENABLE": 24,

        "ADDR_LED_RED": 25,
        "LEN_LED_RED": 1,

        "ADDR_GOAL_POSITION": 30,
        "LEN_GOAL_POSITION": 2,

        "ADDR_PRESENT_POSITION": 36,
        "LEN_PRESENT_POSITION": 2,

        "ADDR_MAX_VELOCITY": 32,
        "LEN_MAX_VELOCITY": 2,

        "DXL_MINIMUM_POSITION_VALUE": 0,
        "DXL_MAXIMUM_POSITION_VALUE": 1023,
...
    }
...

You will also need to change the protocol as the new "2.0" is used but AX12+ is not compatible. You can change this to "1.0" here:

dynamixel_hotplug_ros2_python/src/motor_controller/motor_controller/u2d2_dyna_controller.py

Line 183 in 52f2a30

self.PROTOCOL_VERSION: str = "2.00"

.

Because I do not have access to an AX series nor the 1.0 protocol, I would gladly accept a PR adding support to the AX series, and making the "1.0" protocol a ros parameter instead of hard-coded.

PS: The AX12+ seems pretty old and dynamixel advises users transition to XL430-W250 . You might encounter software support issues by using this motor.

[2lian]

PSS: If you want me to make you a branch with those changes to try out, I can quickly make this as it is not that difficult. However you'll need to debug it in case of issues because I do not have access to the motor.

[mrRobot62]

Hi, uh, thanks for your very quick responses. Why do I use AX12 Servos - because I have three old Bionical-Robotis Kits from the past university time :-).

For "private use" Dynamixels are to expensive to by a bunch. So I will stay and use my AX12. And yes find support for them is a challenge :-)

I forked your repo - in this case I can "play around" the software.

BTW: Ubuntu ist not a RT-OS, do you know: is the communication between PI and Dynamixels with half duplex UART robust enough for a robot with ROS2?

Idea behind: the physical control of the Dynas via an ESP32 (as Actuator & Sensor Node) and then only a simple communication (like RS485) between PI and several ESP32s. ESP32 & AX12+ works on my workbench. RS485 to be able to send broadcast messages to all ESP32

[2lian]

For "private use" Dynamixels are to expensive to by a bunch. So I will stay and use my AX12. And yes find support for them is a challenge :-)

I forked your repo - in this case I can "play around" the software.

I very well understand the struggle. Yes please play around with the repo.

BTW: Ubuntu is not a RT-OS, do you know: is the communication between PI and Dynamixels with half duplex UART robust enough for a robot with ROS2?

Idea behind: the physical control of the Dynas via an ESP32 (as Actuator & Sensor Node) and then only a simple communication (like RS485) between PI and several ESP32s. ESP32 & AX12+ works on my workbench. RS485 to be able to send broadcast messages to all ESP32

I don't know about that. I use the usb u2d2 module from robotis https://www.robotis.us/u2d2/ and it was more than enough for my walking robot. If you just need position control to simply set some angles below 100Hz for sure you don't need to worry.