THE AUV PIRAJUBA
Pirajuba is a AUV with 1.78m in length, 0.234m in maximum diameter that has the "Myring" geometry (Myring, 1976), which has already been applied in the investigation of aircraft’s fuselage and other AUVs such as Maya and Remus (Prestero, 2001).
The vehicle has autonomy of four hours at cruising speed of 1m/s.
The embedded systems are grouped in three pressure vessels, consisting by cylinders of aluminum: the main, which includes the control, sensing and energy systems; the maneuver vessel, which includes the servo-actuators of rudders and corresponding drive electronics; and the propulsion vessel, with include the motor reducer system of the propeller actuation. The three vessels are linked by sea connectors and grouped in a glass-fiber hull flooded ("free-flooding"). The embedded system in the main pressure vessel is arranged in a rack structure of nylon, with longitudinal metallic elements of bulkhead union (which also are of nylon).
The hardware architecture includes a central unit based on a PC/104, and a number of distributed units based on a microprocessor boards. The main unit performs the principal tasks during the mission as the acquisition of data from sensors, navigation, guidance, control and management of the mission.The embedded sensors are an Inertial Measurement Unit (IMU), a GPS receiver, a module of electronic compass TCM2, a depth sensor, current sensors in the actuators and a liquid level sensor. The IMU, compass and GPS have RS232 standard output and are read directly by the central unit.
The actuation system consists of four "high torque" futaba servos and a servo motor of 150W. All actuators are controlled from an Ethernet network link. And to make the interface between the actuators input (PWM and +10V) and the Ethernet network were used RCM4200 modules, which have capacity of A/D conversion and PWM generation. TheRCM4200 modules also make the interface with analog sensors in general, as the depth sensor, the current sensors, andthe liquid presence sensors.
The protocol used in the Ethernet network is the UDP-IP, exchanging messages in the ASCII format standard among the main unit and the other nodes. On the same network is found the data link, which is a 9Xtend-pkg-E Ethernet RF modem, that has a bandwidth of 115Kbps and connects the embedded network and the base station when the vehicle is near the surface.
The base station consists of a PC with a Linux based operating system that execute a program to capture the commands on a joystick, display on screen the states of AUV and send commands to the embedded system.