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*low level* messages in ROS (Indigo)

asked 2017-04-03 08:42:39 -0500

matansar gravatar image

Hello everyone,

I'm beginner in ROS and I have a question about the messages in ROS. Are there low level messages in ROS? For example, if i want to move the robot to location (x,y), I need to send a MoveBaseGoal message. I want to know if there is a way to see messages that directly go to motor (if they exist)?


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answered 2017-04-03 11:59:30 -0500

ahendrix gravatar image

Most robots implement a cmd_vel topic with the geometry_msgs/Twist type which commands the linear and angular velocities of your mobile base. This isn't quite raw motor commands, but it's much closer to an actuator command.

Some robots perform the conversion from cmd_vel to raw motor commands in the driver node or on the embedded motor controller board, and some robots do the conversion to raw motors commands in a ROS nodes and publish additional topics that are then passed to the motor control node. You'll need to refer to the documentation for your specific robot to find out how it does this. (You may also be able to figure out by inspecting the list of topics when your robot is running)

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I have tried to find some documentation about my robot. I works on Armadillo robot (robotican, Indigo). Do you know some links for documentation? Thanks!

matansar gravatar image matansar  ( 2017-04-04 02:50:50 -0500 )edit

A quick search on the ROS wiki finds and , and this tutorial for sending cmd_vel :

ahendrix gravatar image ahendrix  ( 2017-04-04 14:21:55 -0500 )edit

answered 2017-04-03 22:54:08 -0500

updated 2017-04-03 22:59:13 -0500

you can set the logger to rospy.DEBUG, there are many other levels like rospy.DEBUG, rospy.INFO, rospy.WARN, rospy.ERROR, and rospy.FATAL.

  log4cxx::LoggerPtr my_logger =
    log4cxx::Logger::getLogger( ROSCONSOLE_DEFAULT_NAME );

and log everthing with the object my_logger

the official doc is more descriptive

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I don't see how this answers the question of how to send commands to a robot's motors.

ahendrix gravatar image ahendrix  ( 2017-04-03 23:37:51 -0500 )edit

But this logger is related to regular msgs, isn't? I want to know if there are ways to research lower level msgs, like direct commands to the motor.

matansar gravatar image matansar  ( 2017-04-04 02:49:30 -0500 )edit

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Asked: 2017-04-03 08:42:39 -0500

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Last updated: Apr 03 '17