Gazebo Controllers Configuration

This repository explains systematic steps for setting Gazebo controllers config file to properly start spawned robots controllers. This content completes the previous two repos rrr_arm and rrr_arm_config. The first shows a simple arm built from primitive geometry and interfaced wih Gazebo. The second explains how to use MoveIt assistant with the simple arm.

I noticed an issue with MoveIt's setup assistant that is the auto generated controllers config files do not work directly as expected. This results in starting Gazebo with arms fallen down. I will explain the systematic steps to get a join controlled from writing the joint model to launching its controller.

The joint definition starts at the URDF file. Let's assume a joint of type revolute. The definition of the joint should be similar to the following

<joint name="right_arm_shoulder_pan_joint" type="revolute">
    <parent link="right_arm_shoulder" />
    <child link="right_arm_shoulder_pan_link" />
    <origin xyz="0 0.025 0" rpy="0 0 0" />
    <limit lower="-1.57" upper="1.57" effort="10" velocity="3" />
    <axis xyz="0 0 1" />
</joint>

Define a transmission with the name of the joint in the URDF

<transmission name="tran1">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="right_arm_shoulder_pan_joint">
        <hardwareInterface>EffortJointInterface</hardwareInterface>
    </joint>
    <actuator name="motor1">
        <hardwareInterface>EffortJointInterface</hardwareInterface>
        <mechanicalReduction>1</mechanicalReduction>
    </actuator>
</transmission>

Write the control.yaml file. There is a convention to use the joint_name_position_controller. For example: right_arm_shoulder_pan_joint_position_controller.

# Publish all joint states
joint_state_controller:
  type: joint_state_controller/JointStateController
  publish_rate: 50  
  
# Position Controllers
right_arm_shoulder_pan_joint_position_controller:
  type: effort_controllers/JointPositionController
  joint: right_arm_shoulder_pan_joint
  pid: {p: 100.0, i: 0.01, d: 10.0}

Notice the above control config is without a namespace, which will eliminate a lot of confusion specially if multi-arm system is to be controlled. The confusion with namespace is because it needs to be set in the control.yaml, passed as an argument in the controller spawner node, and the robot state publisher joint should remap its default /joint_states to /namespace/joint_states. **It is recommended to avoid namespaces and make use of expressive joint names that show the arm/robot to which the joint belongs. **

Notice it is normal that control.yaml file gets huge as we control multi-arm systems or arms with multi-finger hands. Be careful to list all the controllers as described above. A single typo in the control.yaml is enough not to get any joint controller launched.

Write the controller spawner launch file

<?xml version="1.0"?>
<launch>
    <!-- Load joint controller configurations from YAML file to parameter server -->
    <rosparam file="$(find robot_pkg)/config/control.yaml" command="load" />
    <!-- load the controllers -->
    <node name="controller_spawner" pkg="controller_manager" type="spawner" respawn="false" output="screen" args="right_arm_shoulder_pan_joint_position_controller" />
</launch>

Notice all the controllers should follow in the above controller_spawner node args like args="right_arm_shoulder_pan_joint_position_controller left_shoulder_pan_joint_position_controller " and so on ...

Common errors with controllers setting:

Error:

Controller Spawner: Waiting for service controller_manager/load_controller
[WARN] [1629886820.301987, 290.848000]: Controller Spawner couldn't find the expected controller_manager ROS interface.

Solution: Install pre-requisite packages of your ROS distro

sudo apt install ros-$ROS_DISTRO-ros-control*

This command installs ros-control and ros-controllers packages. If the previous error persists and you are using namespaces in the control.yaml file, double check the points where the namespace should be included (point 3 above).

Error:

Could not switch controllers due to resource conflict.

Solution: The reason is that the same joint is assigned to different controllers. Make sure there is a single controller per joint.

Robotawi/gazebo-controllers-config

Gazebo Controllers Configuration

Common errors with controllers setting:

References: