# Medusa

The vehicles, Medusa Autonomous Marine Vehicles, are autonomous submerged/semi-submerged robotic vehicles developed at the Laboratory of Robotics and Systems in Engineering and Science (LARSyS)/ISR of the Instituto Superior Técnico of Lisbon, Portugal.

## Physics:

Each Medusa class vehicle weighs approximately 30[Kg] in air and consists of two acrylic housing tubes of size 150[mm] by 1035[mm] (diameter x length) with Aluminum end caps, attached to a central Aluminum frame. The distance between the two bodies is 150[mm].

 Height 875[mm] Width 350[mm] Length 1035[mm] Bodies diameter 150[mm] Weight in air from 27[Kg] Energy 830[Wh] LIPO battery cluster Endurance 11 hours at 1.5 knots Propulsion system Diver version: 4 thruster

roll and pitch do not need to be actuated because of the buoyancy, which guarantee that the vehicle has large enough metacentric height. Since the first version of this vehicle was intended to be a surface craft, in the state which is $\text{Medusa}_S$, the heave motion is not being controlled as well. By the aid of two vertical thrusters, the $\text{Medusa}_D$ vehicle is intended to be a diving vehicle as the heave motion is being controlled independently of horizontal motion.

## Hardware:

The lower underwater tube contains two packs of 7-cell lithium polymer batteries together with the thruster electronics, an underwater camera, an acoustic modem (Tritech UK) which provides range measurements to other beacons, and other minor sensors. The upper body, partially out of the water, contains the main computer unit (Epic computer NANO PV D5251, with an Intel Atom D525 dual-core processor, low power, 1.8GHz with 2GB RAM and 64GB solid state disk drive) together with navigation sensors which are an attitude sensor – VECTORNAV VN-100 providing roll, pitch, and yaw ($\phi,\theta,\psi$) of the Medusa with respect to the inertial frame and bod-fixed angular velocity vector, and a Global Positioning System (GPS – Ashtech MB100) which provides the position of the Medusa in inertial frame.

Attached to the main frame there are two stern thrusters (SEABOTIX HPDC1507 Brushless thrusters), which control directly the surge and yaw motions. Moreover a model of thruster is used to get an estimate of the forward velocity of the vehicle, in the body frame, given the rotational speed of the propellers (rpm) of thruster. At the nominal speed of 1.0[m/s], the vehicles have an autonomy of 12 hours. The maximum speed of the vehicles is 1.5 [m/s]. Inner vehicle and vehicle/underwater target communications are enabled via Wi-Fi and an acoustic modem network, respectively.

• Epic computer NANO PVD5251, with an Intel Atom D525 dual-core processor, low power, 1.8GHz with 2GB RAM
• 64GB Solid State Disk
• Attitude sensor – VECTORNAV VN-100
• Global Positioning System (GPS – Ashtech MB100)
• Two packs in parallel of 7-cell Lithium polymer batteries (7S2P). Each cell has 3.7[V] nominal voltage, 330[g] weight, 16Ah, Total weight: 4.6[Kg], Total capacity: 830[Wh]
• Echo-Sounder (Tritech Micron)
• Acoustic modem (Tritech UK)
• Two stern thrusters (SEABOTIX HPDC1507 Brushless thrusters)