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Nodes

control_mux.py

Selects the highest priority (lowest priority value) control_options and publish as control_input

Subscribed topics:

• control_options: an all_seaing_interfaces/ControlMessage message with all the options for the control input.

Published topics:

• cmd_vel: a geometry_msgs/Twist message with the chosen control input.

controller_server.py

Hosts ROS action servers for controlling the boat (e.g waypoint following) with an internal PID controller.

Subscribed topics:

• odometry/filtered: a nav_msgs/Odometry message containing the (filtered) robot odometry.

Published topics:

• control_options: an all_seaing_interfaces/ControlOption message which contains the desired robot twist.
• control_marker: a visualization_msgs/Marker message for visualization.

Parameters:

• global_frame_id: string parameter. Specifies the id of the global frame. Defaults to odom.
• Kpid_x, Kpid_y, Kpid_theta: double array parameters. [Kp, Ki, Kd] values for the robot's x, y, theta movements.
• max_vel: double array parameter. The desired maximum [x, y, theta] velocities of the robot.

Action servers:

• waypoint: an all_seaing_interfaces/Waypoint action server for following the requested [x, y, theta] values. The theta value can be ignored if ignore_theta = True. The threshold values determine how close the robot must be to the target [x, y, theta] for the service to be completed.

xdrive_controller.py

Converts the cmd_vel Twist message to thruster values based on the boat's dimensions and the center of mass. See here for the detailed math.

Subscribed topics:

• cmd_vel: a geometry_msgs/Twist message with the robot's velocity.

Published topics:

• thrusters/front_left/thrust, thrusters/front_right/thrust, thrusters/back_left/thrust, thrusters/back_right/thrust: std_msgs/Float64 messages to send thruster PWM commands.

Parameters:

• front_right_xy, back_left_xy, front_left_xy, back_right_xy: double array parameters. The [x, y] coordinates of each thruster. The positive x direction corresponds to the "forward" direction and the positive y direction corresponds to the "left" direction.
• thruster_angle: double parameter. Angle of the thrusters in degrees (e.g. 60 if facing 15 degrees "more forward").
• drag_constants: double array parameter. The empirically determined [x, y, theta] constants representing the value $\frac{1}{2}\rho c_dA$ where $\rho$ is the fluid density, $c_d$ is the drag coefficient, and $A$ is the reference area.
• output_range: double array parameter. The [min, max] range of the output thruster values (e.g. [1100, 1900] for the pixhawk PWM range).
• smoothing_factor: double parameter. Let this value be $\alpha$. Then, $x_n\leftarrow\alpha x_{n-1}+(1-\alpha) x_n$ where $x_n$ is the thrust output at timestep $n$.