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Vehicle Control Overview#

Overview of the vehicle control system architecture and integration with Autoware.

System Architecture#

The vehicle control system bridges Autoware's high-level planning with low-level actuator control.

Data Flow: 

Autoware Control → Control Commands → Actuator Node → PCA9685 (I2C) → Motor/Steering
                                           ↓
                        Hall Effect Sensor → Velocity Report Node → Velocity Status
                                           ↓
                        IMU Sensor → Yaw Rate Feedback (for steering)

Software Components#

Autoware Control Stack (src/universe/autoware.universe/control/): 

trajectory_follower_node       # Computes control commands from trajectory
       ↓
vehicle_cmd_gate               # Safety gate
       ↓
/control/command/control_cmd   # Control command topic

Vehicle Interface (src/vehicle/autosdv_vehicle_launch/autosdv_vehicle_interface/): 

Actuator Node (actuator.py)
  ├─ Subscribes: /control/command/control_cmd
  ├─ Subscribes: /vehicle/status/velocity_status (for speed feedback)
  ├─ Subscribes: /sensing/imu/imu_data (for yaw rate feedback)
  ├─ Multi-mode longitudinal controller (4 modes)
  ├─ Dual-mode lateral controller (2 modes based on speed)
  └─ Outputs PWM signals to PCA9685 (I2C)

Velocity Report Node (velocity_report.py)
  ├─ Reads: Hall effect sensor (KY-003) on GPIO pin
  ├─ Calculates velocity from wheel rotation
  └─ Publishes: /vehicle/status/velocity_status

Component Roles#

Actuator Node#

Converts Autoware control commands to PWM signals for motor and steering.

Responsibilities: - Subscribe to control commands from Autoware - Implement multi-mode longitudinal controller (speed control) - Implement dual-mode lateral controller (steering control) - Send PWM signals to PCA9685 via I2C - Monitor velocity and IMU feedback - Ensure safe operation with watchdog timers

Velocity Report Node#

Measures vehicle speed using hall effect sensor.

Responsibilities: - Read hall effect sensor pulses from GPIO - Calculate velocity from wheel rotation - Publish velocity reports for feedback control - Provide velocity data to Autoware stack

PCA9685 PWM Driver#

Hardware interface to ESC and servo.

Responsibilities: - Receive I2C commands from actuator.py - Generate PWM signals at 60 Hz - Drive motor ESC (channel 0) and steering servo (channel 1)

Topic Architecture#

Key Topics#

Topic Type Description Rate
/control/command/control_cmd AckermannControlCommand Throttle, brake, steering commands 10 Hz
/vehicle/status/velocity_status VelocityReport Current velocity from sensor 20 Hz
/vehicle/status/control_mode ControlModeReport Manual/Auto mode 1 Hz
/vehicle/command/actuation_cmd Custom PWM values to PCA9685 10 Hz
/sensing/imu/imu_data Imu IMU data for yaw rate feedback 100 Hz

Subscriptions (Actuator Node)#

  • ~/input/control_cmd - Control commands from Autoware
  • ~/input/velocity_status - Current vehicle velocity (for speed control feedback)
  • ~/input/imu - IMU data for yaw rate feedback (steering control)

Publications (Actuator Node)#

  • ~/debug/control_values - Debug control values
  • ~/debug/pwm_values - Debug PWM outputs
  • ~/debug/pid_values - Debug PID state

Autoware Integration#

Control Command Flow#

  1. Planning: Autoware's planning stack generates target trajectory
  2. Control: trajectory_follower_node converts trajectory to control commands
  3. Safety Gate: vehicle_cmd_gate applies safety checks and mode switching
  4. Vehicle Interface: Actuator node converts commands to PWM
  5. Hardware: PCA9685 drives motor ESC and steering servo
  6. Feedback: Velocity and IMU data flow back to controllers

Control Modes#

MANUAL (0): RC controller or keyboard control - Control commands from external sources - Direct PWM control via controller GUI

AUTO (1): Autoware autonomous control - Control commands from trajectory follower - Safety limits enforced by vehicle_cmd_gate

Switching: 

# Switch to AUTO mode
ros2 service call /vehicle/set_control_mode autoware_auto_vehicle_msgs/srv/ControlModeCommand "{mode: 1}"

# Switch to MANUAL mode
ros2 service call /vehicle/set_control_mode autoware_auto_vehicle_msgs/srv/ControlModeCommand "{mode: 0}"

Safety Features#

Control Mode Gate#

  • Enforces velocity limits (0-3 m/s)
  • Enforces steering angle limits (±0.5 rad)
  • Enforces acceleration limits (±2 m/s²)
  • Rejects commands outside safe ranges

Watchdog Timer#

Actuator Node includes watchdog timer:

# actuator.py watchdog implementation
last_command_time = time.time()
TIMEOUT_SECONDS = 1.0

def check_watchdog():
    if time.time() - last_command_time > TIMEOUT_SECONDS:
        # No command for 1 second → EMERGENCY STOP
        pwm.set_pwm(0, 0, 370)   # Motor: dead zone
        pwm.set_pwm(1, 0, 400)   # Steering: center

Additional timeout: Vehicle interface monitors velocity feedback - If no feedback for >2 seconds → publish STOP command - Ensures vehicle stops even if communication fails

Emergency Stop#

Trigger: 

# Publish zero velocity
ros2 topic pub /control/command/control_cmd autoware_auto_control_msgs/AckermannControlCommand "{
  longitudinal: {speed: 0.0, acceleration: -5.0}
}" -1

# Or switch to MANUAL mode
ros2 service call /vehicle/set_control_mode ... "{mode: 0}"

Behavior: - Maximum braking applied (PWM 340) - Steering held at current angle - Control mode switches to MANUAL

Hardware Summary#

Component Interface Details
PCA9685 I2C (0x40, bus 1) 16-channel PWM, 60 Hz
Motor ESC PWM (channel 0) Range: 280-460, Init: 370
Steering Servo PWM (channel 1) Range: 350-450, Init: 400
Hall Effect Sensor GPIO KY-003, velocity measurement
IMU ROS topic Yaw rate feedback for steering

For detailed hardware specifications, see Hardware.

Configuration Files#

  • Actuator parameters: src/vehicle/autosdv_vehicle_launch/autosdv_vehicle_interface/params/actuator.yaml
  • Velocity report parameters: src/vehicle/autosdv_vehicle_launch/autosdv_vehicle_interface/params/velocity_report.yaml
  • Vehicle information: src/param/autoware_individual_params/.../vehicle_info.param.yaml

Next Steps#