Hardware Architecture

The Otter ASV is a 2 meters long catamaran propelled by two electrical fixed thrusters. This means that steering has to be done through differential thrust by the controller.

The control box is based around a Raspberry Pi 4 with 4GB of RAM. Connected through it's GPIO pins is a Strato Pi CAN board that provides a robust power supply in addition to multiple communications interfaces and an independent hardware watchdog. A CAN network connects the Raspberry Pi to the Torqeedo Interface card. Thus it has access to both power channel and motor control. There is a passive PoE injector providing power for the external BulletAC IP67. It also contains a SLIM interface board that synchronizes and reads the RS-485 serial communication from the TBR-700 -/RT hydrophone.

The thrusters used by the Otter are two Ultralight 403 motors by Torqeedo. They can provide a maximum propulsive power of 180 W each, and would be the equivalent of 1HP each according to the manufacturer. It can do a maximum of 1200rpm at the propeller, and has a gear ration of 7:1.

The batteries are of the shelf Torqeedo batteries developed for use with their electrical outboard motors. The Otter can carry four of these batteries, for a total capacity of 3660Wh, or 124Ah. This provides the Otter with up to 20 hours of battery powered operation, depending on speed and payload(according to Maritime Robotics).

Delivered by Maritime Robotics, the hull is designed to be light and portable. At 200cm length and 108cm width, transport and handling can become an issue, but the Otter solves this by being built in a highly modular way. According to the manufacturer, it's possible to disassemble it into parts of under 20Kg each, making it possible to move it by a single person.

Inner dimensions: HxLxW=8×23.7x49cm

Overview:

Detailed wiring:

There is also fuses between the Torqeedo secondary power lines and everything that goes outside the control box, but that is for simplicity left out of the diagram.

• Strato Pi CAN setup