Error cannot load message class for

I have seen the other topics about the similar error (like here http://answers.ros.org/question/10897… ), but they don’t seem to fit to my problem.

I am using Ubuntu 12.04 and ROS Hydro.

I have a robotino_node which is publishing several things. They show up if I use rostopic list. i also can use rostopic type and rostopic info, here the robotino_node is listed as a publisher.
But if I use rostopic hz or rostopic echo the error form the topic line shows up, eg

Cannot load message class for [robotino_msgs/PowerReadings]. Are your messages built?

rosmsg show does also work, eg

[robotino_msgs/PowerReadings]
time stamp
float current
float voltage

Now interestingly if I try rostopic echo with «bumper», which is the only std_msg published by the robotino_node it shows one time

data: False
---

but that’s it.

I suspect that my cmake file for the messages is wrong, but I am not sure; it looks like this

# CATKIN_MIGRATION: removed during catkin migration
# cmake_minimum_required(VERSION 2.8.3)
project(robotino_msgs)

find_package(catkin REQUIRED COMPONENTS geometry_msgs std_msgs message_generation roscpp)

include_directories(include
 ${catkin_INCLUDE_DIRS}
)

add_message_files(
FILES
AnalogReadings.msg
BHAReadings.msg
DigitalReadings.msg
EncoderReadings.msg
GrapplerReadings.msg
GripperState.msg
MotorReadings.msg
NorthStarReadings.msg
PowerReadings.msg
SetBHAPressures.msg
SetBHAPressures.msg
SetGrapplerAxes.msg
SetGrapplerAxis.msg)

add_service_files(
FILES
ResetOdometry.srv
SetEncoderPosition.srv
SetGripperState.srv)

#add_dependencies(robotino_msgs geometry_msgs_generate_messages_cpp) #or yes?
#target_link_libraries(robotino_msgs  ${catkin_LIBRARIES} ) # or yes
## Generate added messages and services with any dependencies listed here
generate_messages(
   DEPENDENCIES geometry_msgs std_msgs
)

# catkin_package parameters: http://ros.org/doc/groovy/api/catkin/html/dev_guide/generated_cmake_api.html#catkin-package
# TODO: fill in what other packages will need to use this package
catkin_package(
   DEPENDS roscpp geometry_msgs std_msgs
   CATKIN_DEPENDS # TODO
   INCLUDE_DIRS # TODO include
   LIBRARIES # TODO
)

My launch file looks like this

    <launch>
      <arg name="hostname" default="172.26.1.1" />

        <node name="robotino_node" pkg="robotino_node" type="robotino_node" output="screen">
            <param name="hostname" value="$(arg hostname)" />
            <param name="max_linear_vel" value="0.5" />
            <param name="min_linear_vel" value="0.05" />
            <param name="max_angular_vel" value="3.0" />
            <param name="min_angular_vel" value="0.1" />
    <!--        <param name="downsample_kinect" value="true" />
            <param name="leaf_size_kinect" value="0.04" />  entfernt da KinectNode nicht aktualisiert-->
            <remap from="robotino_joint_states" to="joint_states" />
            <!--remap from="image_raw" to="image"/-->
        </node>

    <!--
      <node name="robotino_odometry_node" pkg="robotino_node" type="robotino_odometry_node" output="screen">
        <param name="hostname" value="$(arg hostname)" />
      </node>
    -->
    <!--
      <node name="robotino_laserrangefinder_node" pkg="robotino_node" type="robotino_laserrangefinder_node" output="screen">
        <param name="hostname" value="$(arg hostname)" />
        <param name="laserRangeFinderNumber" value="0" />
      </node>
    -->

    <!--
      <node name="robotino_camera_node" pkg="robotino_node" type="robotino_camera_node" output="screen">
        <param name="hostname" value="$(arg hostname)" />
        <param name="cameraNumber" value="0" />
      </node>
    -->

        <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher" output="screen">
            <param name="publish_frequency" type="double" value="20.0" />
        </node>

    <!--
      <node name="robotino_mapping_node" pkg="robotino_node" type="robotino_mapping_node" output="screen">
        <param name="hostname" value="$(arg hostname)" />
      </node>

-->

    <!--node pkg="tf" type="static_transform_publisher" name="laser_link_broadcaster" args="0.12 0 0.025 0 0 0 base_link laser_link 50" /-->

    <param name="robot_description" textfile="$(find robotino_description)/urdf/robotino.urdf" />
</launch>

So even if just the std_msgs work, shouldn’t at least the bumper published with … (more)

3 Answers

I know this is very late, but I just encountered the exact same problem. My problem originated from not having the .msg file added in my CMake file when I built. Here is how I resolved it:

First, ensure the file has been added to the CMakeLists.txt (yours already has)

Second, clean your build by running «catkin_make clean» in the root of your workspace.

Third, remake your project with «catkin_make»

Lastly, resource the devel/setup.bash in your workspace.

I know this is not a great answer, but I encountered the exact same problem where rosmsg could find my message, but rostopic could not, and these are the exact steps I took that resolved it.

Please Check your ROS_PACKAE_PATH. Make sure you run rostopic echo on your workspace executing terminal. Try following,

1. roscd or cd ~/catkin_ws
2. source devel/setup.bash
3. rostopic echo /topic

Source source devel/setup.bash from your Catkin workspace.

Other answer mentions this among many other things to look at, but really this is the only thing you need to do if your packages run and communicate and only rostopic is a problem.

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