Rowbot Control

Controls the rowbot in Gazebo.

Requirements

As well as the standard rowbot requirements, this package also needs:

• rowbot_msgs
• shapely (pip install shapely)

How it works

• twist_to_drive is a velocity controller, accepting twist messages on '/cmd_vel'. It publishes motor commands on 'left_thrust_cmd' and 'right_thrust_cmd'.
• course_to_twist is a course controller, which controls the vessel's speed and heading. It subscribes to 'cmd_course' and publishes to '/cmd_vel'.
• waypoint_control uses either Pure Pursuit or NLGL to output a target point, which the vessel aims for. For pure pursuit, this is the next waypoint. For NLGL this is a virtual target point, which is designed to bring the robot closer to the waypoint path.

Running rowbot_control

Option 1 - basic operation

To launch the course controller for Gazebo:

roslaunch rowbot_control low_level_control.launch

You can then publish a desired course using:

 rostopic pub -r 10 /cmd_course rowbot_msgs/Course  '{speed: 1.0, yaw: 0.0}'

• Speed is in m/s
• yaw is measured CCW from East (ENU standard)

Option 2 - Waypoint Following

Ensure to not launch move_base or navigation when running this - #TODO make compatible.

To launch the waypoint following controller (this also launches the course controller):

roslaunch rowbot_control waypoint_control.launch

This controller listens for a nav_msgs/Path message on the topic /waypoints, when it receives a path message it will follow the path until it is completed.

The following parameters can be added to the waypoint_control.launch folder as private parameters for the navigate_wamv.py node:

• speed: the speed of the vehicle
• use_nlgl: Whether to use non-linear guidance law
• nlgl_radius: The radius for the NLGL algorithm - a larger number means more stability, a smaller number will turn towards the path more aggressively.
• tolerance: The allowable distance to the waypoint which will trigger the waypoint
• speed_control: Whether to use speed control - in dev, not working well.
• braking_distance: If speed control is on, the distance from the waypoint to start braking.
• minimum_forwards_speed: If speed control is on, the lower limit on the forwards speed
• request_mode: options:
  • 'hard': reaches the waypoints regardless
  • 'soft': if it veers to far from the path, or if it misses a waypoint. Requests more waypoints (and stops)
• allowable_distance_to_path: if request_mode is soft, the maxmimum distance from the path allowed until new waypoints are requested.

To send it some testing waypoints, use the simple_waypoints package:

roslaunch simple_waypoints simple_waypoints.launch

Known bugs

• When using low-level-control, at tight waypoints it will go backwards slightly