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Diagram

sequenceDiagram
    participant MR as Mission Runner
    participant OM as Orca Manager
    participant BT as Behavior Tree
    box Nav2 Plugins
    participant P as Planner
    participant C3D as Controller 3D
    participant GC as Goal Checker
    participant PC as Progress Checker
    end
    participant BC as Base Controller
    participant MA as MAVROS/ArduSub

    MR->>MR: Define waypoints[1]
    MR->>OM: Set AUV mode[2]
    OM->>MA: Set ALT_HOLD mode[3]
    OM->>BC: Enable control[4]
    MR->>BT: Send waypoints[5]
    BT->>P: Request path[6]
    P->>BT: Return 3D path[7]
    loop Until all waypoints reached
        BT->>C3D: Follow path[8]
        C3D->>BC: Publish vel cmds[9]
        BC->>BC: Read SLAM pose[10]
        BC->>MA: Publish RC override[11]
        MA->>BC: Publish local position[12]
        MA->>OM: Publish vehicle state[13]
        BC->>BT: Publish motion and odometry[14]
        BT->>GC: Check goal[15]
        Note over BT,PC: Progress Checker used internally[16]
        GC->>BT: Goal status[17]
    end
    BT->>MR: All waypoints reached[18]
    MR->>OM: Set ROV mode[19]
    OM->>MA: Set MANUAL mode[20]
    OM->>BC: Disable control[21]
Loading
  1. Mission Runner: Define waypoints
  2. Mission Runner: Set AUV mode
  3. Orca Manager: Set ALT_HOLD mode
  4. Orca Manager: Enable control
  5. Mission Runner: Send nav goal
  6. Behavior Tree: Request path
  7. Planner: Return 3D path
  8. Behavior Tree: Follow path
  9. Controller: Publish vel cmds
  10. Base Controller: Read SLAM pose
  11. Base Controller: Publish RC override
  12. MAVROS/ArduSub: Publish local position
  13. MAVROS/ArduSub: Publish vehicle state
  14. Base Controller: Publish motion and odometry
  15. Behavior Tree: Check goal
  16. Progress Checker: Check progress (internal to Nav2)
  17. Goal Checker: Goal status
  18. Mission Runner: Goal reached
  19. Mission Runner: Set ROV mode
  20. Orca Manager: Set MANUAL mode
  21. Orca Manager: Disable control

Orca4 Nav2 Plugins

The following Nav2 plugins provide basic 3D planning and control suitable for open water. They all ignore the global and local costmaps. They all largely ignore yaw, though the PurePursuitController3D will generate a value for yaw (angular.z) in cmd_vel.

Note for Humble: Nav2 now includes a velocity smoother node which takes cmd_vel output from the Nav2 controller(s) and does velocity, acceleration, and deadband smoothing. This node isn't 3D-aware, so it isn't used in Orca4.

StraightLinePlanner3D

The StraightLinePlanner3D plugin is similar to the StraightLinePlanner plugin. The planner can plan in two segments (vertical motion first, then horizontal) or one segment (vertical and horizontal motion combined).

Parameters:

Parameter Type Default Notes
planning_dist double 0.1 How far apart the plan poses are, m
z_before_xy bool false If true plan in 2 segments: z then xy

PurePursuitController3D

The PurePursuitController3D plugin is similar to the PurePursuitController plugin. It limits horizontal, vertical and yaw acceleration to reduce pitching and drift. The BlueROV2 frame is holonomic, but forward/backward drag is lower than the left/right drag, so the controller generates diff-drive motion (linear.x, linear.z and angular.z).

Parameters:

Parameter Type Default Notes
xy_vel double 0.4 Desired horizontal velocity, m/s
xy_accel double 0.4 Max horizontal acceleration, m/s^2
z_vel double 0.2 Desired vertical velocity, m/s
z_accel double 0.2 Max vertical acceleration, m/s^2
yaw_vel double 0.4 Desired yaw velocity, r/s
yaw_accel double 0.4 Max yaw acceleration, r/s^2
lookahead_dist double 1.0 Lookahead distance for pure pursuit algorithm, m
transform_tolerance double 1.0 How stale a transform can be and still be used, s
goal_tolerance double 0.1 Stop moving when goal is closer than goal_tolerance. Should be less than the values in GoalChecker3D
tick_rate double 20 The BT tick rate, used to calculate dt

ProgressChecker3D

The ProgressChecker3D plugin is similar to the SimpleProgressChecker plugin.

Parameters:

Parameter Type Default Notes
radius double 0.5 Minimum distance to move, m
time_allowance double 10.0 Time allowed to move the minimum distance, s

GoalChecker3D

The GoalChecker3D plugin is similar to the SimpleGoalChecker plugin.

Parameters:

Parameter Type Default Notes
xy_goal_tolerance double 0.25 Horizontal goal tolerance
z_goal_tolerance double 0.25 Vertical goal tolerance