data_pub

Data Pub

The data_pub package contains scripts that interface with various sensors, currently interfacing with the DVL (Doppler Velocity Log), pressure sensor (depth), voltage sensor, and temperature/humidity. You can launch all nodes in this package using the pub_all.launch file.

Additionally, the package allows control over the marker dropper servo. The servo is controlled by publishing a Bool message to the servo_control service.

Config File

This package contains a config file for each robot, stored at config/<ROBOT_NAME>.yaml, where <ROBOT_NAME> is the value of the ROBOT_NAME enviornment variable corresponding to each robot. Config files for all robots must be structured as below:

dvl:
  ftdi: DVL_FTDI_string
  negate_x_vel: true or false
  negate_y_vel: true or false
  negate_z_vel: true or false

There must be only one top-level key, dvl. Under it, there must be the following keys:

• ftdi: The FTDI string that uniquely identifies the DVL for that robot and can be used to find the port the DVL is connected to.
• negate_x_vel: Boolean indicating whether the DVL's X velocity should be negated by the dvl_to_odom script before being published.
• negate_y_vel: Boolean indicating whether the DVL's Y velocity should be negated by the dvl_to_odom script before being published.
• negate_z_vel: Boolean indicating whether the DVL's Z velocity should be negated by the dvl_to_odom script before being published.

DVL

We use the Teledyne Pathfinder DVL for velocity measurements. The DVL is connected to the robot's main computer via a USB serial converter.

The dvl_raw script publishes the raw DVL data to the /sensors/dvl/raw topic with type custom_msgs/DVLRaw. It obtains the DVL's FTDI string from the config file mentioned above and uses it to find the DVL's port.

The dvl_to_odom script converts the raw DVL data and publishes it to /sensors/dvl/odom with type nav_msgs/Odometry for use in sensor_fusion. It obtains the DVL's negation values from the config file mentioned above and uses them to negate the DVL's X, Y, and Z velocities before publishing the odometry message.

You can launch both scripts using the pub_dvl.launch file.

External Sensors

The pressure Arduino obtains data from the Blue Robotics Bar02 Pressure Sensor and a generic voltage sensor and sends the data as raw serial messages to the robot's main computer.

To connect to the pressure Arduino, the pressure_voltage.py script obtains its FTDI string from the config file for the current robot (as indicated by the ROBOT_NAME environment variable) in the offboard_comms package. The FTDI string is used to find the pressure Arduino's port.

The data obtained from serial contains tags P: and V: identifying pressure (depth) and voltage, respectively.

The pressure_voltage.py script can be launched using the pub_pressure_voltage.launch file.

Pressure/Depth

The depth data obtained is filtered, converted into a geometry_msgs/PoseWithCovarianceStamped message, and published to the /sensors/depth topic, for use in sensor_fusion.

Two filters are applied to the depth:

1. Values with absolute value greater than 7 are ignored.
2. A median filter is applied to the 3 most recent values.

These filters are applied to eliminate noise in the data that would otherwise result in an inaccurate Z position in state.

All data in this PoseWithCovarianceStamped message is set to 0 except for the pose.pose.position.z value, which is set to the depth in meters. The pose.pose.orientation is set to the identity quaternion. Except for the pose.pose.position.z value, all other values are unused in sensor_fusion.

Voltage

The same node also gets voltage data from the voltage sensor on the same arduino and is published as a Float64 to /sensors/voltage, without modification.

Temperature/Humidity

On a different Arduino, both temperature and humidity readings are gathered by a DHT11 sensor, dumped over serial, and published to the /sensors/temperature and /sensors/humidity topics, respectively. The data is published as a Float64.

The data obtained from serial contains tags T: and H: identifying temperature and humidity, respectively.

Temperature is measured in degrees Fahrenheit and humidity is measured in percentage.

The servo_sensors.py script can be launched using the pub_servo_sensors.launch file. This Arduino also houses the servo for the marker dropper, and is designed to be a general-purpose sensor Arduino for future use.

Servo

The servo_control service allows control over the marker dropper servo. The marker dropper holds two rounds that can be dropped individually. The service takes a Bool message with the following values:

• True: Drop the "left" round.
• False: Drop the "right" round.