Messages and Topics¶

The Rover gateway bridges CAN bus messages with ROS2 topics, using both standard ROS2 messages (like geometry_msgs/Twist) and custom messages defined in the gateway_msgs package. All topics use the /rover/ namespace prefix.

Messages¶

The gateway uses both standard and custom ROS2 messages. All messages in the gateway_msgs/ package are custom.

geometry_msgs/Twist¶

Vehicle control message containing linear and angular velocity components.

Message Definition:

geometry_msgs/Vector3 linear
geometry_msgs/Vector3 angular

Field Usage:

linear.x (float64): Forward/backward throttle command
Range: -1.0 to 1.0
-1.0 = full reverse, 0.0 = neutral, 1.0 = full forward
Internally converted to PWM pulse width (1000-2000µs, 1500µs neutral)
angular.z (float64): Steering angle in radians
Range: ±π/4 radians (±45 degrees)
Positive = right turn, negative = left turn
Other fields: Unused by Rover

Safety Notes:

Physical radio overrides all /rover/cmd_vel commands when active
Direction changes require stopping at neutral for 2 seconds
Values are validated and clamped to safe ranges

gateway_msgs/BatteryStatus¶

Battery monitoring with cell voltages, output power, and regulated power.

Message Definition:

# Cell voltages in millivolts
uint16[] cell_voltages_mv

# Battery output voltage in millivolts
uint32 output_voltage_mv

# Battery output current in milliamps
uint32 output_current_ma

# Regulated output voltage in millivolts
uint32 regulated_voltage_mv

# Regulated output current in milliamps
uint32 regulated_current_ma

Field Details:

cell_voltages_mv: Array of 6 values for individual cells (LiPo battery)
output_voltage_mv: Raw battery pack output voltage
output_current_ma: Current being drawn from battery
regulated_voltage_mv: Voltage after regulation (5V/3.3V rails)
regulated_current_ma: Current on regulated outputs

CAN Mapping:

Cell voltages split across two CAN messages (3 cells each)
Published only when both messages received

gateway_msgs/WheelStatus¶

Wheel speed and RPM information.

Message Definition:

# Wheel RPM (revolutions per minute)
float32 rpm

# Wheel speed in kilometers per hour
float32 speed_kph

Field Details:

rpm: Raw wheel rotation speed
speed_kph: Calculated linear speed (based on wheel diameter)

gateway_msgs/ObstacleDistance¶

Distance measurements from ultrasonic sensors.

Message Definition:

# Distance readings in millimeters for each sensor
# Array of 4 distance values
uint16[] distances_mm

Field Details:

distances_mm: Array of exactly 4 measurements in millimeters
Each element corresponds to a sensor position (left to right)
Value of 0 may indicate sensor error or out-of-range

gateway_msgs/CANStatus¶

CAN bus communication status.

Message Definition:

# Whether CAN communication is enabled
bool can_enabled

# Timestamp when the status was last updated
uint64 timestamp

Field Details:

can_enabled: True when CAN active, False when disabled
timestamp: Microsecond timestamp of status update

Usage:

CAN is disabled during FREEZE action mode or LISTEN_ONLY/SILENT communication modes
Used by firmware update utility to pause operation of all modules

gateway_msgs/ReportFrequency¶

Configuration for sensor reporting frequency.

Message Definition:

# Frequency in Hz for sensor reporting
uint32 frequency_hz

Field Details:

frequency_hz: Desired reporting frequency
Valid range: 1-100 Hz
Out-of-range values are clamped

Topics¶

Topics follow the pattern:

/rover/<node_name>/<message_type>

For multi-instance components (wheels, batteries, obstacle detectors):

/rover/<component>_<position>/<message_type>

Control Topics¶

/rover/cmd_vel¶

Type: geometry_msgs/Twist

Direction: Subscribed by gateway

QoS: RELIABLE

Purpose: Control commands for throttle and steering

Example:

# Drive forward at half speed with slight right turn
ros2 topic pub /rover/cmd_vel geometry_msgs/Twist \
  "linear: {x: 0.5, y: 0.0, z: 0.0}
   angular: {x: 0.0, y: 0.0, z: 0.349}"

Python Example:

from geometry_msgs.msg import Twist
import math

cmd = Twist()
cmd.linear.x = 0.5    # 50% forward throttle
cmd.angular.z = math.radians(20)  # 20 degrees right
publisher.publish(cmd)

Monitoring Topics¶

Read-only topics

All topics in this section are published by the gateway. Do not publish to these topics - they are for monitoring only.

/rover/radio/cmd_vel¶

Type: geometry_msgs/Twist

Direction: Published by gateway

QoS: BEST_EFFORT

Purpose: Radio control commands (published when physical radio active)

Battery Monitor Topics¶

Instances:

battery_monitor_control_system - Control system battery
battery_monitor_ad_system - Autonomous driving system battery

/rover/battery_monitor_*/cell_voltages¶

Type: gateway_msgs/BatteryStatus

QoS: BEST_EFFORT

Purpose: Individual cell voltages

Example:

ros2 topic echo /rover/battery_monitor_control_system/cell_voltages

/rover/battery_monitor_*/output¶

Type: gateway_msgs/BatteryStatus

QoS: BEST_EFFORT

Purpose: Battery output voltage and current

/rover/battery_monitor_*/regulated¶

Type: gateway_msgs/BatteryStatus

QoS: BEST_EFFORT

Purpose: Regulated output voltage and current

Wheel Topics¶

Instances:

wheel_front_left
wheel_front_right
wheel_rear_left
wheel_rear_right

/rover/wheel_*/wheel_status¶

Type: gateway_msgs/WheelStatus

QoS: BEST_EFFORT

Purpose: Wheel speed and RPM

Example:

# Monitor front left wheel
ros2 topic echo /rover/wheel_front_left/wheel_status

Obstacle Detector Topics¶

Instances:

obstacle_detector_front
obstacle_detector_rear

/rover/obstacle_detector_*/obstacle_distance¶

Type: gateway_msgs/ObstacleDistance

QoS: BEST_EFFORT

Purpose: Distance readings from ultrasonic sensors

Example:

ros2 topic echo /rover/obstacle_detector_front/obstacle_distance

/rover/mayor/can_status¶

Type: gateway_msgs/CANStatus

QoS: RELIABLE

Purpose: CAN bus status information

Configuration Topics¶

/rover/wheel_*/report_frequency_hz¶

Type: gateway_msgs/ReportFrequency

QoS: RELIABLE

Direction: Subscribed by gateway

Purpose: Configure wheel reporting frequency

Instances:

wheel_front_left
wheel_front_right
wheel_rear_left
wheel_rear_right

Example:

# Set to 50 Hz
ros2 topic pub /rover/wheel_front_left/report_frequency_hz \
  gateway_msgs/ReportFrequency "{frequency_hz: 50}"

Topic Discovery¶

List all active Rover topics:

ros2 topic list | grep /rover

Monitor a specific topic:

ros2 topic echo /rover/wheel_front_left/wheel_status

Check topic info:

ros2 topic info /rover/cmd_vel

Get message type details:

ros2 interface show geometry_msgs/Twist
ros2 interface show gateway_msgs/BatteryStatus

Measure topic frequency:

ros2 topic hz /rover/wheel_front_left/wheel_status