fake_joint_driver

This package contains a node to provide hardware_interface::PositionJointInterface, which simply loopback the command joint position to the actual position. In other words, it is faking a perfect joint controller. It can be used from ros_controllers such as JointTrajectoryController. You can check your own joint trajectories on rviz, without using Gazebo or others.

Quick start

launch the nodes

On one terminal, do:

$ roslaunch fake_joint_driver fake-joint-driver.test

This launch file does:

1. Loading robot description of simple 3-DOF arm in robot/arm3.urdf.xacro
2. Launching fake_joint_driver_node and robot_state_publisher
3. Launching controller manager to spawn ros_controllers (joint_state_controller and joint_trajecotry_controller)

See the robot in rviz

On another terminal, do:

$ rviz

Add robot model to see the robot.

Set trajectory with rqt_joint_trajectory_controller

On another terminal, do:

$ rqt

Choose Plugins->Robot tools->Joint trajectory controller to load the plugin. Select controller manager and controller, then you can see sliders to set the joint trajectory goals.

Parameters

• use_robot_description

When it is true, the driver read the parameter /robot_description to obtain the joint list to control by this driver. When it is false, you must specify the joint list by include_joints parameters.

• include_joints

This is the list of the joints which the driver node should control.

• exclude_joints

This is the list of the joints which the driver node should not control.

• start_position

This is a map to specify the initial position of the joint. You can use this to avoid collision in zero joint angle.

Use like:

  <!-- fake_joint_driver_node -->
  <node name="fake_joint_driver" pkg="fake_joint_driver" type="fake_joint_driver_node">
    <!-- Set joint start position -->
    <rosparam param="start_position">{LARM_JOINT2: -1.7, RARM_JOINT2: -1.7}</rosparam>
  </node>

Caution

You can set target joints for joint_trajectory_controller in the config/controllers.yaml. Note somehow you cannot see any controllers and joints in rqt_joint_trajectory_controller if any joints have no joint position limits in URDF file. It is easy to be trapped.

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