diff_drive_controller

Controller for mobile robots with differential drive.

As input it takes velocity commands for the robot body, which are translated to wheel commands for the differential drive base.

Odometry is computed from hardware feedback and published.

For an introduction to mobile robot kinematics and the nomenclature used here, see mobile_robot_kinematics.

Other features

  • Realtime-safe implementation.

  • Odometry publishing

  • Task-space velocity, acceleration and jerk limits

  • Automatic stop after command time-out

  • Chainable Controller

Description of controller’s interfaces

References

When controller is in chained mode, it exposes the following references which can be commanded by the preceding controller:

  • <controller_name>/linear/velocity double, in m/s

  • <controller_name>/angular/velocity double, in rad/s

Together, these represent the body twist (which in unchained-mode would be obtained from ~/cmd_vel). The <controller_name> is commonly set to diff_drive_controller.

Feedback

As feedback interface type the joints’ position (hardware_interface::HW_IF_POSITION) or velocity (hardware_interface::HW_IF_VELOCITY,if parameter position_feedback=false) are used.

Output

Joints’ velocity (hardware_interface::HW_IF_VELOCITY) are used.

ROS 2 Interfaces

Subscribers

~/cmd_vel [geometry_msgs/msg/TwistStamped]

Velocity command for the controller. The controller extracts the x component of the linear velocity and the z component of the angular velocity. Velocities on other components are ignored.

Publishers

~/odom [nav_msgs::msg::Odometry]

This represents an estimate of the robot’s position and velocity in free space.

/tf [tf2_msgs::msg::TFMessage]

tf tree. Published only if enable_odom_tf=true

~/cmd_vel_out [geometry_msgs/msg/TwistStamped]

Velocity command for the controller, where limits were applied. Published only if publish_limited_velocity=true

Parameters

This controller uses the generate_parameter_library to handle its parameters. The parameter definition file located in the src folder contains descriptions for all the parameters used by the controller.

An example parameter file for this controller can be found in the test directory: