steering_controllers_library
Library with shared functionalities for mobile robot controllers with steering drive (2 degrees of freedom). The library implements generic odometry and update methods and defines the main interfaces.
Nomenclature used for the controller is used from wikipedia.
Execution logic of the controller
The controller uses velocity input, i.e., stamped or unstamped Twist messages where linear x
and angular z
components are used.
Angular component under
Values in other components are ignored.
In the chain mode the controller provides two reference interfaces, one for linear velocity and one for steering angle position.
Other relevant features are:
support for front and rear steering configurations;
odometry publishing as Odometry and TF message;
input command timeout based on a parameter.
The command for the wheels are calculated using odometry
library where based on concrete kinematics traction and steering commands are calculated.
Currently implemented kinematics in corresponding packages are:
Description of controller’s interfaces
References (from a preceding controller)
<controller_name>/linear/velocity [double], in m/s
<controller_name>/angular/position [double] # in [rad]
Commands
front_steering == true
<front_wheels_names[i]>/position [double] # in [rad]
<rear_wheels_names[i]>/velocity [double] # in [m/s]
front_steering == false
<front_wheels_names[i]>/velocity [double] # in [m/s]
<rear_wheels_names[i]>/position [double] # in [rad]
States
Depending on the position_feedback
, different feedback types are expected
position_feedback == true
–>TRACTION_FEEDBACK_TYPE = position
position_feedback == false
–>TRACTION_FEEDBACK_TYPE = velocity
front_steering == true
<front_wheels_names[i]>/position [double] # in [rad]
<rear_wheels_names[i]>/<TRACTION_FEEDBACK_TYPE> [double] # in [m] or [m/s]
front_steering == false
<front_wheels_names[i]>/<TRACTION_FEEDBACK_TYPE> [double] # [m] or [m/s]
<rear_wheels_names[i]>/position [double] # in [rad]
Subscribers
Used when controller is not in chained mode (in_chained_mode == false
).
<controller_name>/reference [geometry_msgs/msg/TwistStamped] If parameter
use_stamped_vel
istrue
.<controller_name>/reference_unstamped [geometry_msgs/msg/Twist] If parameter
use_stamped_vel
isfalse
.
Publishers
<controller_name>/odometry [nav_msgs/msg/Odometry]
<controller_name>/tf_odometry [tf2_msgs/msg/TFMessage]
<controller_name>/controller_state [control_msgs/msg/SteeringControllerStatus]
Parameters
This controller uses the generate_parameter_library to handle its parameters.
For an exemplary parameterization see the test
folder of the controller’s package.
- reference_timeout (double)
Timeout for controller references after which they will be reset. This is especially useful for controllers that can cause unwanted and dangerous behaviour if reference is not reset, e.g., velocity controllers. If value is 0 the reference is reset after each run.
Default: 1.0
- front_steering (bool)
Is the steering on the front of the robot?
Default: true
- rear_wheels_names (string_array)
Names of rear wheel joints.
Constraints:
length is less less 5
contains no duplicates
parameter is not empty
- front_wheels_names (string_array)
Names of front wheel joints.
Constraints:
length is less less 5
contains no duplicates
parameter is not empty
- rear_wheels_state_names (string_array)
(Optional) Names of rear wheel joints to read states from. If not set joint names from ‘rear_wheels_names’ will be used.
Default: {}
Constraints:
length is less less 5
contains no duplicates
- front_wheels_state_names (string_array)
(Optional) Names of front wheel joints to read states from. If not set joint names from ‘front_wheels_names’ will be used.
Default: {}
Constraints:
length is less less 5
contains no duplicates
- open_loop (bool)
Choose if open-loop or not (feedback) is used for odometry calculation.
Default: false
- velocity_rolling_window_size (int)
The number of velocity samples to average together to compute the odometry twist.linear.x and twist.angular.z velocities.
Default: 10
- base_frame_id (string)
Base frame_id set to value of base_frame_id.
Default: “base_link”
- odom_frame_id (string)
Odometry frame_id set to value of odom_frame_id.
Default: “odom”
- enable_odom_tf (bool)
Publishing to tf is enabled or disabled?
Default: true
- twist_covariance_diagonal (double_array)
diagonal values of twist covariance matrix.
Default: {0.0, 7.0, 14.0, 21.0, 28.0, 35.0}
- pose_covariance_diagonal (double_array)
diagonal values of pose covariance matrix.
Default: {0.0, 7.0, 14.0, 21.0, 28.0, 35.0}
- position_feedback (bool)
Choice of feedback type, if position_feedback is false then
HW_IF_VELOCITY
is taken as interface type, if position_feedback is true thenHW_IF_POSITION
is taken as interface typeDefault: false
- use_stamped_vel (bool)
Choice of vel type, if use_stamped_vel is false then
geometry_msgs::msg::Twist
is taken as vel msg type, if use_stamped_vel is true thengeometry_msgs::msg::TwistStamped
is taken as vel msg typeDefault: false