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Navigation System
To navigate the Stingray to each of the objectives, the planner node calculates the necessary bearing and depth that the vehicle needs to maintain in order to get to the target. These target values are passed to the navigation node where the controls software performs the command based on sensor data from the IMU and depth sensor.
Compass
An Ocean server OS-50003-axissolid state compass is used to determine the attitude of the vehicle. The compass uses a combination of magnetometers and accelerometers to determine the angles of pitch, roll, and yaw where the latter is used as a compass heading. These values are output from the compass as an ASCII stream via USB.
Depth Sensor
A SSI Technologies P51-15-S-B-I36-4.5V-R pressure sensor is used to measure the depth of the vehicle relative to the surface of the water. The 0.5 - 4.5V DC output voltage range supplied by the depth sensor is measured by using the Labjack data acquisition card. The depth sensor output voltage corresponds to a pressure in the range 14.7 - 29.5 psi. Given the finite resolution of the Labjack voltage measurement, the final resolution of the depth measurements is within 2.44mm.
Controls Software
In order to maintain target values for pitch, roll, yaw and depth, the Stingray implements a number of proportional-integral-derivative (PID) loops. These loops use sensor data from the IMU, depth sensor, vision, and sonar for feedback to control each of the propulsion actuators.
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