# ENDURUNS: An Integrated and Flexible Approach for Seabed Survey Through Autonomous Mobile Vehicles
## 3 System Functionalities
### Hybrid Underwater Autonomous Vehicle  
The ENDURUNS underwater vehicle is a torpedo shaped AUV with gliding capability. It has been designed with a modular approach, implemented as cylindrical sections, connected one to each other, leading to different AUV configurations according to the mission needs. Special effort was spent for a design with a minimal amount of protrusions, therefore the vehicle steering, in both horizontal and vertical plane, is obtained through a suitable modulation of the four rear thrusters. Moreover, in order to simplify the construction, the vehicle hull is wet and the electronic components are contained in pressure resistant cylinders. The remaining inner parts are filled with appropriate syntactic foam.  
Figure 2 shows an overview of the vehicle, where the section (a) corresponds to the propulsion module containing the four thrusters and related servo boards, (b) the navigation module containing the housings with the avionics and the acoustic modem for the AUV/USV communication, (c) the primary energy module containing two battery housings acting as moving ballast in gliding mode, (d) the secondary energy module containing the fuel cell and the associated gas storage containers, (e) the payload module containing the inductive charger and the mission camera and finally the (f) nose module containing the forward looking sonar and the variable buoyancy system. The propulsion, navigation and primary energy modules must be always present, as they provide the basic functionalities of motion, sensing, processing and energy. The remaining modules can be added or removed depending on the specific application context.  
The gliding capability is provided by three main components: (i) a variable buoyancy system, positioned at the vehicle bow, module (a), for maximizing the change of pitch of the vehicle associated with the variation of buoyancy; (ii) a mobile ballast in the rear section, module (c), allowing to maintain a predetermined pitch during both ascending and descending steps for maximizing the vehicle performance during gliding navigation; (iii) two wings for increasing the lift, with symmetrical profile, positioned at the centre line of the vehicle to not induce hydrodynamic effects during the navigation phases in AUV mode.  
Table 4 summarises the most relevant components and sensors necessary for the navigation, installed onboard the AUV.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Component** & **Model** & **Description** \\ \hline Thrusters & Model 500 AUV, Teenadyne & propeller specifically developed for submarine vehicles. The forward force at 3 knots is about 12 kg! \\ \hline Doppler Velocity Log (DVL) & 500, Nortek & it provides the AUV altitude from the bottom between 0.3 m and 200 m \\ \hline Inertial Navigation System (INS) & Phins C3, iXBlue, & based on FOG (Fiber Optic Gyro) technology it provides very accurate angular measurements and position estimations \\ \hline Acoustic Modem and USBL transponder & SACR 18/34H, EvoLogics & AUV/USV underwater acoustic communication with additional functionality of acoustic transponder \\ \hline Depthmeter & PA-33k, [PERSON] & nominal accuracy of 0.02\% of its maximum value \\ \hline Attitude and Heading Reference System (AHRS) & Orientus, Advanced & it measures the heading and attitude of the vehicle only while gliding \\ \hline GPS receiver & NEO-6M-001, Ublox & it computes the absolute AUV position at sea surface \\ \hline Inductive charger & Magellrom, WiSub & allows data transfer and power when the AUV and USV are docked. \\ \hline \hline \end{tabular}
\end{table}
Table 4: The main AUV navigation components and sensors.