[ros2] Port skid_steer_drive to ROS2

[shiveshkhaitan]

Differential drive plugin has been modified to integrate skid steer drive into it. Any number of wheel pairs (1: diff drive, 2: skid_steer_drive or greater than 2) can be specified in the sdf and accordingly the joint names, wheel separations, and wheel diameters have to be specified.
Example:

      <plugin name='diff_drive' filename='libgazebo_ros_diff_drive.so'>

        <ros>
          <namespace>/demo</namespace>
          <argument>cmd_vel:=cmd_demo</argument>
          <argument>odom:=odom_demo</argument>
        </ros>

        <!-- Number of wheel pairs -->
        <num_wheel_pairs>2</num_wheel_pairs>
        
        <!-- wheels0 -->
        <left_joint0>left_wheel_joint0</left_joint0>
        <right_joint0>right_wheel_joint0</right_joint0>
        
        <!-- wheels1-->
        <left_joint1>left_wheel_joint1</left_joint1>
        <right_joint1>right_wheel_joint1</right_joint1>

        <!-- kinematics -->
        <wheel_separation0>1.25</wheel_separation0>
        <wheel_separation1>1.25</wheel_separation1>

        <wheel_diameter0>1.0</wheel_diameter0>
        <wheel_diameter1>0.6</wheel_diameter1>

        <!-- limits -->
        <max_wheel_torque>20</max_wheel_torque>
        <max_wheel_acceleration>1.0</max_wheel_acceleration>

        <!-- output -->
        <publish_odom>true</publish_odom>
        <publish_odom_tf>true</publish_odom_tf>
        <publish_wheel_tf>true</publish_wheel_tf>

        <odometry_frame>odom_demo</odometry_frame>
        <robot_base_frame>chassis</robot_base_frame>

      </plugin>

Here there are 2 wheel pairs specified. Thus it will behave as skid steer drive. Similarly any number can be specified for num_wheel_pairs. The joint names, wheel separations, and wheel diameter for each pair has to be specified with their index number appended to the base tag.

For example <wheel_separation3> specifies the spacing for <left_joint3> and <right_joint3> and so. The indexing starts from 0 to (num_wheel_pairs - 1).

[chapulina]

Works for me, and I love the demo vehicle!

Mind adding a note to the wiki about migrating the skid steer plugin?

Also, don't forget to remove the skid steer files from .ros1_unported.

[shiveshkhaitan]

Migration guide is available at ROS 2 Migration: Skid Steer drive

[chapulina]

Works great for me, thanks for iterating 😄

[LihanChen2004]

May I ask if the modified controller supports translational movement similar to the 4WD Mecanum?

I used the description file of nexus_4wd_mecanum_simulator and replace the original control plugin with the libgazebo_ros_diff_drive.so plugin in ROS2 Humble. However, it seems to have some directional issues.

When I send a clockwise rotation command, it actually moves forward.
Moreover, there is no movement at all when I issue left or right translation commands.

<gazebo>
<plugin name='skid_steer_drive' filename='libgazebo_ros_diff_drive.so'>
    <ros>
      <namespace>/</namespace>
      <remapping>cmd_vel:=cmd_vel</remapping>
      <remapping>odom:=odom</remapping>
    </ros>

    <num_wheel_pairs>2</num_wheel_pairs>

    <left_joint>lower_left_wheel_joint</left_joint>
    <right_joint>lower_right_wheel_joint</right_joint>

    <left_joint>upper_left_wheel_joint</left_joint>
    <right_joint>upper_right_wheel_joint</right_joint>

    <wheel_separation>0.6</wheel_separation>
    <wheel_separation>0.6</wheel_separation>

    <wheel_diameter>0.4</wheel_diameter>
    <wheel_diameter>0.4</wheel_diameter>

    <max_wheel_torque>3</max_wheel_torque>
    <max_wheel_acceleration>6.0</max_wheel_acceleration>

    <publish_odom>false</publish_odom>
    <publish_odom_tf>false</publish_odom_tf>
    <publish_wheel_tf>true</publish_wheel_tf>
    <odometry_frame>odom</odometry_frame>
    <robot_base_frame>base</robot_base_frame>

</plugin>
</gazebo>