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BlueBoat USV

BlueBoatUSV BlueBoatUSV2

The BlueBoat USV (Unmanned Surface Vehicle) is a small autonomous watercraft developed by Blue Robotics. It is designed for various marine applications including navigation experiments, environmental monitoring, and autonomous surface operations.

System Overview

The BlueBoat is a compact, versatile unmanned surface vehicle that provides an excellent platform for marine robotics research and development. Its modular design allows for extensive customization with various sensors and payloads.

Key Features

  • Marine-Grade Design: Waterproof and corrosion-resistant construction
  • Autonomous Capabilities: GPS navigation and waypoint following
  • Modular Payload Bay: Customizable sensor and equipment mounting
  • Long Endurance: Extended operation time for marine missions
  • Remote Control: Manual override and telemetry capabilities
  • Open Source: Hardware and software designs available for customization

Specifications

  • Length: Approximately 1.2m
  • Beam (Width): 0.6m
  • Draft: 0.15m (shallow water capable)
  • Weight: ~25kg (varies with payload)
  • Max Speed: ~5 knots (2.5 m/s)
  • Endurance: Several hours (battery dependent)
  • Communication: Long-range radio telemetry

Components

Propulsion System

  • Motors: Two thruster motors for differential thrust control
  • left_motor: Port side propulsion unit
  • right_motor: Starboard side propulsion unit
  • Propellers: Optimized for efficiency and maneuverability
  • Control: Variable speed control with reverse capability

Hull Design

  • Catamaran Configuration: Twin-hull design for stability
  • Buoyancy: Positive buoyancy with safety margins
  • Payload Bay: Central compartment for sensors and electronics
  • Waterproofing: Sealed electronics compartments

Available Sensors

  • GPS: High-precision positioning for navigation
  • IMU: 9-axis inertial measurement unit for orientation
  • Camera: Optional visual monitoring and recording
  • Depth Sensor: Water depth measurement capability
  • Environmental Sensors: Temperature, pH, conductivity (optional)

Control Interface

The BlueBoat USV integrates seamlessly with Simulink through the webots-simulink bridge:

% Motor control functions
wb_motor_set_velocity.m     % Set thruster velocities
wb_motor_get_position.m     % Get motor positions
wb_robot_step.m             % Main simulation step

% Sensor interface functions
wb_gps_get_values.m         % GPS position data
wb_imu_get_values.m         % Orientation and acceleration
wb_camera_get_image.m       % Visual data acquisition

The control system implements:

  1. Waypoint Navigation: GPS-based path following
  2. Station Keeping: Position holding against currents
  3. Heading Control: Compass-based directional control
  4. Speed Control: Velocity regulation for efficiency

Control System Design

System Block Diagram

flowchart TB
    subgraph Reference["Reference Inputs"]
        R1[/"Position Reference<br/>(x_d, y_d)"/]
        R2[/"Heading Reference<br/>(ψ_d)"/]
        R3[/"Velocity Reference<br/>(u_d)"/]
    end

    subgraph Guidance["Guidance System"]
        WP[Waypoint<br/>Manager]
        LOS[Line-of-Sight<br/>Algorithm]
        PP[Path<br/>Planner]
    end

    subgraph Navigation["Navigation System"]
        GPS[GPS<br/>Receiver]
        IMU[IMU<br/>Sensor]
        COMP[Compass]
        EKF[Extended<br/>Kalman Filter]
    end

    subgraph Control["Control System"]
        subgraph OuterLoop["Outer Loop - Position"]
            PC[Position<br/>Controller]
        end
        subgraph MiddleLoop["Middle Loop - Heading"]
            HC[Heading<br/>Controller]
        end
        subgraph InnerLoop["Inner Loop - Velocity"]
            VC[Velocity<br/>Controller]
        end
    end

    subgraph Actuators["Propulsion System"]
        MIX[Differential<br/>Thrust Mixer]
        LM[Left<br/>Motor]
        RM[Right<br/>Motor]
    end

    subgraph Plant["USV Dynamics"]
        USV[BlueBoat<br/>Vehicle]
    end

    R1 --> WP
    WP --> LOS
    LOS --> PP
    PP --> PC
    R2 --> HC
    R3 --> VC

    PC --> HC
    HC --> VC
    VC --> MIX

    MIX --> LM
    MIX --> RM
    LM --> USV
    RM --> USV

    USV --> GPS
    USV --> IMU
    USV --> COMP
    GPS --> EKF
    IMU --> EKF
    COMP --> EKF

    EKF --> PC
    EKF --> HC
    EKF --> VC

    style Reference fill:#e1f5fe
    style Guidance fill:#fff3e0
    style Navigation fill:#f3e5f5
    style Control fill:#e8f5e9
    style Actuators fill:#ffebee
    style Plant fill:#fce4ec

State-Space Model

The BlueBoat USV dynamics are modeled using a 6-DOF state-space representation:

flowchart LR
    subgraph Inputs["Control Inputs u"]
        U1["τ_u (Surge Force)"]
        U2["τ_r (Yaw Moment)"]
    end

    subgraph StateSpace["State-Space Model<br/>ẋ = Ax + Bu<br/>y = Cx"]
        subgraph States["State Vector x"]
            S1["x - North Position"]
            S2["y - East Position"]
            S3["ψ - Heading Angle"]
            S4["u - Surge Velocity"]
            S5["v - Sway Velocity"]
            S6["r - Yaw Rate"]
        end
    end

    subgraph Outputs["Outputs y"]
        Y1["Position (x, y)"]
        Y2["Heading (ψ)"]
        Y3["Velocities (u, v, r)"]
    end

    Inputs --> StateSpace
    StateSpace --> Outputs

    style Inputs fill:#ffcdd2
    style StateSpace fill:#c8e6c9
    style Outputs fill:#bbdefb

State-Space Matrices

%% BlueBoat USV State-Space Model
% State vector: x = [x, y, psi, u, v, r]'
% x, y: Position in NED frame [m]
% psi: Heading angle [rad]
% u: Surge velocity [m/s]
% v: Sway velocity [m/s]
% r: Yaw rate [rad/s]

% Physical Parameters
m = 25;           % Mass [kg]
Iz = 5;           % Yaw moment of inertia [kg*m^2]
L = 1.2;          % Length [m]
B = 0.6;          % Beam width [m]

% Hydrodynamic Coefficients (linearized)
Xu = -5;          % Surge damping [N*s/m]
Yv = -20;         % Sway damping [N*s/m]
Nr = -2;          % Yaw damping [N*m*s/rad]

% Added Mass
Xu_dot = -2;      % Surge added mass [kg]
Yv_dot = -10;     % Sway added mass [kg]
Nr_dot = -1;      % Yaw added mass [kg*m^2]

% Effective mass/inertia
m_u = m - Xu_dot;
m_v = m - Yv_dot;
Iz_r = Iz - Nr_dot;

% Linearized State-Space Matrices (at constant velocity U0)
U0 = 1.0;  % Nominal surge velocity [m/s]

% A matrix (6x6) - System dynamics
A = [0, 0, -U0, 1, 0, 0;
     0, 0,  U0, 0, 1, 0;
     0, 0,   0, 0, 0, 1;
     0, 0,   0, Xu/m_u, 0, 0;
     0, 0,   0, 0, Yv/m_v, 0;
     0, 0,   0, 0, 0, Nr/Iz_r];

% B matrix (6x2) - Input mapping
B = [0, 0;
     0, 0;
     0, 0;
     1/m_u, 0;
     0, 0;
     0, 1/Iz_r];

% C matrix (6x6) - Full state output
C = eye(6);

% D matrix (6x2) - No direct feedthrough
D = zeros(6, 2);

% Create state-space system
sys = ss(A, B, C, D);
sys.StateName = {'x', 'y', 'psi', 'u', 'v', 'r'};
sys.InputName = {'tau_u', 'tau_r'};
sys.OutputName = {'x', 'y', 'psi', 'u', 'v', 'r'};

Control Architecture Detail

flowchart TB
    subgraph HeadingControl["Heading Control Loop"]
        PSI_D[/"ψ_d<br/>(Desired Heading)"/]
        PSI[/"ψ<br/>(Actual Heading)"/]
        ERR_PSI((+<br/>-))
        PID_H[PID Controller<br/>Kp=2.0, Ki=0.1, Kd=0.5]
        TAU_R["τ_r<br/>(Yaw Moment)"]

        PSI_D --> ERR_PSI
        PSI --> ERR_PSI
        ERR_PSI --> PID_H
        PID_H --> TAU_R
    end

    subgraph VelocityControl["Velocity Control Loop"]
        U_D[/"u_d<br/>(Desired Velocity)"/]
        U[/"u<br/>(Actual Velocity)"/]
        ERR_U((+<br/>-))
        PID_V[PID Controller<br/>Kp=50, Ki=5, Kd=10]
        TAU_U["τ_u<br/>(Surge Force)"]

        U_D --> ERR_U
        U --> ERR_U
        ERR_U --> PID_V
        PID_V --> TAU_U
    end

    subgraph ThrustAllocation["Differential Thrust Allocation"]
        ALLOC[Thrust<br/>Allocator]
        T_L["T_L<br/>(Left Thrust)"]
        T_R["T_R<br/>(Right Thrust)"]

        TAU_U --> ALLOC
        TAU_R --> ALLOC
        ALLOC --> T_L
        ALLOC --> T_R
    end

    subgraph Equations["Thrust Allocation"]
        EQ1["T_L = (τ_u/2) - (τ_r/B)"]
        EQ2["T_R = (τ_u/2) + (τ_r/B)"]
    end

    style HeadingControl fill:#e3f2fd
    style VelocityControl fill:#f3e5f5
    style ThrustAllocation fill:#fff8e1
    style Equations fill:#f5f5f5

Line-of-Sight Guidance

flowchart LR
    subgraph LOSGuidance["LOS Guidance Algorithm"]
        WP1["Waypoint k<br/>(x_k, y_k)"]
        WP2["Waypoint k+1<br/>(x_{k+1}, y_{k+1})"]
        POS["Current Position<br/>(x, y)"]

        ALPHA["Path Angle<br/>α_k = atan2(y_{k+1}-y_k, x_{k+1}-x_k)"]

        CROSS["Cross-Track Error<br/>e = -(x-x_k)sin(α_k) + (y-y_k)cos(α_k)"]

        DELTA["Lookahead Distance<br/>Δ"]

        PSI_D["Desired Heading<br/>ψ_d = α_k + atan(-e/Δ)"]
    end

    WP1 --> ALPHA
    WP2 --> ALPHA
    POS --> CROSS
    ALPHA --> CROSS
    CROSS --> PSI_D
    DELTA --> PSI_D
    ALPHA --> PSI_D

    style LOSGuidance fill:#e8f5e9

Marine Vehicle Dynamics

The BlueBoat follows marine vehicle dynamics principles:

% Surge motion (forward/backward)
X = thrust_force - drag_force

% Yaw motion (turning)
N = differential_thrust * beam_width/2

% Simple heading control
heading_error = desired_heading - current_heading;
rudder_command = Kp * heading_error;

Differential Thrust Control

The BlueBoat uses differential thrust for maneuvering:

# Forward movement
left_motor_speed = base_speed
right_motor_speed = base_speed

# Turn right
left_motor_speed = base_speed + turn_rate
right_motor_speed = base_speed - turn_rate

# Reverse
left_motor_speed = -base_speed
right_motor_speed = -base_speed

GPS Waypoint Following

The BlueBoat implements several navigation modes:

  1. Direct Navigation: Straight-line path to target
  2. Waypoint Following: Sequential waypoint navigation
  3. Loiter Mode: Circular pattern around a point
  4. Return-to-Launch: Automatic return to start position

Environmental Adaptation

  • Current Compensation: Drift correction using GPS feedback
  • Wind Resistance: Heading adjustments for wind effects
  • Wave Response: Motion filtering for sensor stability

Mission Planning

Typical Mission Profiles

  1. Environmental Monitoring:
  2. Water quality sampling along transects
  3. Temperature and pH measurement

  4. Pollution detection and mapping

  5. Bathymetric Surveys:

  6. Depth mapping using sonar
  7. Underwater terrain modeling

  8. Harbor and coastal surveys

  9. Search and Rescue Support:

  10. Visual search patterns
  11. Emergency equipment delivery

  12. Communication relay operations

  13. Research Applications:

  14. Marine biology data collection
  15. Oceanographic measurements
  16. Long-term environmental monitoring

Usage Examples

Basic Operation

  1. Setup: Load the BlueBoat world file in Webots
  2. Configuration: Set desired sensors in the body_slot
  3. Mission Planning: Define waypoints and mission parameters
  4. Execution: Launch autonomous mission or manual control
% Example mission parameters
mission_waypoints = [
    0, 0;       % Start position
    100, 0;     % First waypoint
    100, 100;   % Second waypoint
    0, 100;     % Third waypoint
    0, 0        % Return home
];

% Control loop
for i = 1:length(mission_waypoints)
    navigate_to_waypoint(mission_waypoints(i,:));
    wait_for_arrival();
end

Sensor Integration

The BlueBoat's modular design allows for various sensor configurations:

  • Basic Configuration: GPS + IMU for navigation
  • Mapping Configuration: + Sonar for bathymetry
  • Monitoring Configuration: + Water quality sensors
  • Research Configuration: + Multiple scientific instruments

Performance Characteristics

Operating Parameters

  • Typical Speed: 2-3 knots for efficient operation
  • Maximum Speed: ~5 knots in calm conditions
  • Turning Radius: ~2 boat lengths minimum
  • Position Accuracy: ±2-5 meters (GPS dependent)
  • Mission Duration: 2-6 hours (battery/fuel dependent)

Environmental Limits

  • Wave Height: Up to 0.5m significant wave height
  • Wind Speed: Up to 15 knots sustained
  • Operating Temperature: -10°C to +50°C
  • Water Depth: Minimum 0.2m depth required

Safety and Regulations

Safety Features

  • Fail-Safe Return: Automatic return on communication loss
  • Low Battery Return: Automatic return at low power
  • Emergency Stop: Remote emergency shutdown capability
  • Status Monitoring: Real-time telemetry and alerts

Regulatory Compliance

  • Maritime Regulations: Comply with local USV regulations
  • Navigation Rules: Follow maritime traffic rules
  • Communication: Maintain VHF radio monitoring
  • Visual Identification: Proper lighting and marking

Applications and Use Cases

Research and Development

  • Algorithm Testing: Navigation and control algorithm validation
  • Sensor Development: New marine sensor integration and testing
  • Multi-Vehicle Operations: Swarm and collaborative behaviors

Commercial Applications

  • Aquaculture: Fish farm monitoring and maintenance
  • Port Operations: Harbor patrol and monitoring
  • Environmental Services: Water quality monitoring and assessment

Educational Applications

  • Marine Robotics Courses: Hands-on USV control and programming
  • Oceanography: Data collection methods and instruments
  • Control Systems: Marine vehicle dynamics and control

References

Educational Purpose: The BlueBoat USV simulation provides an excellent platform for learning marine robotics concepts including marine vehicle dynamics, GPS navigation, environmental monitoring, and autonomous surface operations. The integration with Simulink enables rapid development and testing of marine control algorithms in a realistic virtual environment before deployment on actual hardware.