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AquaUrsa Electrical - 2015

Electrical Platform

The electrical system for AquaUrsa is divided into several 'core' boards. The purpose of this was to make the design more modular and to add multiple layers of redundancy to the system.  The team utilized CadSoft Eagle for the design of the electrical schematics and for the PCB layout.  All of the team's PCBs are fabricated by the wonderful people at Alberta Printed Circuits in Calgary, Alberta, Canada.

 

The overall electrical system architecture is somewhat modified to what was used on the 2014 platform. Its main components are:

  • An ODROID-C1 Quad-Cord ARM board that is responsible for communicating with the various 'nodes' and running the PID controllers and mission planner.
  • An Intel Atom embedded computer (EC) that processes vision data from the forward-facing and downward-facing cameras
  • A power distribution board that steps the 18.5 V lithium-polymer battery output to 12, 5, and 3.3 V to power all electronic components.
  • Motor controllers that are driven by the Motor Control 'node' to send the appropriate PWM signals to the thrusters
  • A sensor 'node' that processes data from the IMU and depth sensor.

 

The 'node' architecture allows for easy expandability, as all the nodes are able to communicate with the main computer (ODROID) via USB. Additional nodes (eg. torpedo node, marker-dropper node, sonar node) can be added as needed.

The custom-designed boards are described further below.

 

Motor Node and Controllers

Without adequate, robust motor control, AquaUrsa would literally be dead in the water. This is indeed the lynch-pin of the entire electrical system. In past years, off-the shelf components were used, but these devices often required unnecessary compromises. Commercial devices often lacked required features like feedback, had an excess of features that complicated their integration, and generally larger form factors.

To address these concerns, ARVP has developed a purpose-built motor controller based on the L298 H-bridge integrated circuit. This IC can drive one motor at 2 A or two motors at 4 A in a “bridged” configuration. Three motor control boards, each with two L298 ICs, are used, allowing up to six thrusters to be operated. Each channel accepts a PWM signal for thrust level and a binary direction signal. Power is passed directly from the 18.5 V batteries to the motor controller boards. In addition to these inputs, a “sense” pin feeds an analog voltage, proportional to motor current draw to the on-board ADC for reading by the motor control board, and an active-high “enable” pin disables the load when pulled low, to implement required kill-switch functionality.

Sensor Node

Numerous sensors allow AquaUrsa to determine its orientation, bearing, and depth, and other mission-specific information:

  • An Ocean Servers OS4000 3-axis compass and accelerometer to determine orientation and heading.
  • An OpenROV IMU/Compass/Depth Sensor used for depth sensor functionality and as a backup for the main IMU.
  • Four SQ26R1 hydrophones positioned at the corners of the frame, for passive sonar.
  • Two USB video cameras used by the embedded computer for image processing.

These sensors are connected the the sensor node, which uses a Teensy 3.1 at it's core for reading data from the sensors, which it passes back to the mission computer.

Sonar Node

AquaUrsa’s passive sonar system enables it to detect to detect the acoustic pinger located at the end of the RoboSub course. Four Cetecean Research SQ26 hydrophones measure audio from the environment. The system is still under development, but the 'brains' of the sonar node is a Beaglebone Black

Power

In previous years, voltages required to power the different electrical components were provided by separate boards. To simplify AquaUrsa’s internal wiring and reduce assembly and troubleshooting times during competition, all of these boards’ functionality has been rolled into a single power distribution board. A dedicated 18.5 V lithium-polymer battery provides input to a Vicor voltage regulator module, which steps the battery voltage down to 12 V, and a Murata regulator provides 5 and 3.3 V. Each of the 12, 5, and 3.3 V outputs can be any required loads using Molex Minifit connectors. Standardizing electronics power to use these connectors will improve organization and consistency of electrical wiring, as well as allowing all of the electronics to be powered by an ATX 2.0 compliant PC power supply during testing, since the connectors follow the ATX2.0 standard.

 

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