Skip to content
This repository has been archived by the owner on Nov 8, 2023. It is now read-only.

Latest commit

 

History

History
65 lines (56 loc) · 3.49 KB

README.md

File metadata and controls

65 lines (56 loc) · 3.49 KB
Raw

Orca3 Base Controller

Orca3 is designed for the BlueRobotics BlueROV2, a simple but powerful ROV (Remotely Operated Vehicle) with two vertical thrusters and four vectored horizontal thrusters. See orca_gazebo for more information.

BaseController

The BaseController node does the following:

  • subscribe to /cmd_vel from the Nav2 system
  • predict motion using a constant acceleration (trapezoidal velocity) model. Roll and pitch are not modeled.
  • publish odometry on /odom, and broadcast the odom->base_link transform
  • subscribe to /barometer and run a PID controller to hold depth at the target value
  • calculate required thrust forces and publish /thrust messages for the Gazebo simulation
  • publish diagnotics on /depth, /motion and /pid_z

Thrust force includes these components:

  • thrust due to acceleration
  • thrust to counteract the predicted drag. I've estimated the drag of the BlueROV2 frame, but this is very rough, and each actual AUV will have different drag properties.
  • thrust to hold depth, this includes a static component based on buoyancy and the output of the PID controller

Motion model parameters

There's a very simple motion model that considers buoyancy and drag. It does not consider added mass, hydrodynamic damping, etc.

Parameter Type Default Notes
mdl_mass double 9.75 Mass, kg
mdl_volume double 0.01 Displacement volume, m^3
mdl_fluid_density double 997 Fluid density, kg/m^3, typically 997 for freshwater, 1027 for seawater
mdl_thrust_scale double 0.7 Global thrust scale, used to boost small thrust values typical for AUV operation
mdl_drag_coef_x double 0.8 Drag coefficient for forward / back motion
mdl_drag_coef_y double 0.95 Drag coefficient for strafing motion
mdl_drag_coef_z double 0.95 Drag coefficient for vertical motion
mdl_drag_partial_const_yaw double 0.004 Drag coefficient for yaw motion
mdl_thrust_dz_pwm int16 35 Thruster deadzone

Control parameters

Parameter Type Default Notes
auto_arm bool false Arm the controller on boot
stamp_msgs_with_current_time bool false Use now() vs Barometer.header.stamp
x_vel double 0.4 Max forward / back velocity, m/s
y_vel double 0.4 Max strafing velocity, m/s
z_vel double 0.2 Max vertical velocity, m/s
x_accel double 0.4 Max forward / back acceleration, m/s^2
y_accel double 0.4 Max strafing acceleration, m/s^2
z_accel double 0.2 Max vertical acceleration, m/s^2
yaw_vel double 0.4 Max yaw velocity, r/s
yaw_accel double 0.4 Max yaw acceleration, r/s^2
map_frame_id string map Map frame id
odom_frame_id string odom Odom frame id
base_frame_id string base_link Base frame id
publish_tf bool base_link Publish odom->base_link transform
thruster_xy_limit double 0.5 Limit the x and y effort in the vectored horizontal thrusters to provide enough pwm range for yaw motion
thruster_accel_limit double 1.0 Limit rapid changes to thruster values
pid_enabled bool true Turn the depth PID controller on or off
pid_z_kp double 0.5 Kp
pid_z_ki double 0 Ki
pid_z_kd double 0 Kd
pid_z_i_max double 0.1 Windup prevention: max acceleration from Ki term, m/s^2
hover_thrust bool true Add static hover thrust to counteract buoyancy