Sparus AUV was built by a group of student in the UdG to face the 2010 edition of SAUC-E. It was designed with the main goal of having a small and simple torpedo-shaped vehicle with hovering capabilities.

Sparus was designed with one vertical thruster for the heave DOF and 2 horizontal thrusters for the surge and yaw DOFs.  The vertical thruster was placed in the centre of the vehicle, where the centre of gravity and buoyancy are located. The horizontal thrusters were placed in the back, separated from the longitudinal axis of the vehicle to generate a torque for the yaw DOF. The mechanical structure and components are therefore organized around this configuration. The front of the vehicle contains all the sensors and the battery housing. The back of the robot contains a second housing for the electronics, computer and the AHRS. Having the batteries in a separate housing increases the weight, length and expense of the vehicle but on the other hand it minimizes the downtime between missions by allowing battery packs to be quickly interchanged. Also, potentially explosive gases that can build up from the batteries do not interfere with sparking and high temperature electronics.

The main structure is made of aluminum profiles and stainless steel clamps that hold the two pressure housings. The battery housing is hold with only one clamp in the top, to allow its easy and fast replacement for a second battery housing. The housings were made of aluminum which easily transmits the internal heat to the environment, it is easy to machine and it is strong enough to withstand the sea pressure (they were designed for 100 m depth). In order to eliminate screws, a 1.8 mm nylon thread before the O-ring secures the end-caps. The electronics housing can be easily opened from the back of the vehicle, allowing the access to the electronics and computer in few minutes.

To give the vehicle the required buoyancy, technical foam is distributed all over the top part of the robot. It is strategically located to place the buoyancy centre at the same longitudinal position as the gravity centre but above it, assuring pitch and roll stability. The vehicle is trimmed with lead weights, in order to bring the gravity centre where the vertical thruster is placed. Small zinc anodes were added to eliminate the corrosion due to sea water and different metals on the vehicle. Finally, to reduce the water drag and to protect the components, a two-part ABS skull covers the AUV.

For connecting all the external components, two types of underwater connectors were used: SubconnR for the high current connections and Lumberg for the low current parts. Also, the umbilical cable, which is often connected and dis- connected, uses a Subconn connector. The main battery switch is IP68 rated and covered with resin. The WiFi adapter, also covered with resin, is placed on the top of the vehicle. It also has the option to be detached to float on the surface while keeping the connection with the AUV through a 5 meter Universal Serial Bus (USB) cable. The final dimensions of the vehicle are 1.22 m length by 0.23 m diameter, and the weight is around 30 kg.

The on-board embedded computer has been chosen as a trade-off between processing power, size and power consumption. An Ultra Low Voltage (ULV) Core Duo processor with the 3.5” small form factor was selected. The vehicle is also equipped with a complete sensor suite composed by two color video cameras (forward-looking and down-looking), a AHRS MTi from XSens Technologies, a Micron imaging sonar from Tritech, an echosounder, a pressure sensor and a DVL from LinkQuest which also includes a compass/tilt sensor. Temperature, voltage and pressure sensors as well as water leakage detectors are installed into the pressure vessels for safety purposes. The on-board computer, the sensors and the three thrusters are powered by two battery packs. The first one, at 12V, powers the computer, the electronics and the sensors. The second one, at 24V, is for the thrusters. Each battery pack has 10Ah of capacity, which allows for an autonomy of 2.5 hours.