The electrical system in this year’s robot is comprised of modular and standardized printed circuit board (PCB) designs, upgraded wiring solutions, and circuit protection improvements. This is all mounted in the same compact, easily removable, 3D printed panels used in last year’s design. This allows the robot to accomplish the tasks it sets out to do reliability and efficiently.
Electrical Power Delivery
Four, 14.8V, 94.72Wh lithium-polymer batteries are used to power the robot; three batteries power the thrusters and one powers the remaining electronics. Each thruster battery is connected to two Zubax Myxa B electronic speed controllers (ESC) and all batteries operate independently from each other. The batteries are housed in two sealable acrylic cylinders, separate from the main hull, and feed the robot through Subconn Power Series waterproof cables, capable of carrying up to 25A per contact.
The computers and embedded systems require either 12V or 5V from a stable source, thus a voltage regulation system is used to convert 14.8V from the battery to the acceptable levels required by the electronics. The regulator board uses two Murata UWE series eighth-brick isolated DC-DC converters which use a step-up/down topology. A small expansion board is mounted to the main regulator board to monitor power output of each rail and sends data through an i2c interface.
PCB Design Standardization
Each embedded system in the robot uses the Teensy 3.2 microcontroller and all have identical communication interfaces if they are required to communicate with the main computers, a Nvidia TX2. This allows for many different backup communication options. During normal operation, UAVCAN is used for reading and commanding the Teensys.
Battery Monitoring Board and Kill-Switch
This board monitors power delivered by the batteries using Texas Instrument’s INA3221 power monitoring integrated circuit (IC). It can also interrupt current flow from the three thruster batteries using low-side NMOS transistor switches, which are turned on only when the kill-switch is activated. The kill-switch uses multiple redundant hall effect sensors to detect the presence of an external neodymium magnet. Only when a magnetic field is detected, the switch allows the transistors to turn on.
Multi-purpose Actuation Board
The primary purpose of this board is to actuate the 12V solenoid valves that launch the 3D printed torpedoes. Low-side NMOS transistors with carefully designed snubber circuits, to minimize high frequency ringing from the solenoid coils during turn-off, are used to actuate the valves. Its secondary functions include RC servo motor and RGB LED strip control, using NSP Semiconductors’ PCA9685 PWM generator IC.
Internal Environment Sensor Board
To monitor the hull’s internal conditions, this board is used to monitor air temperature, pressure, and humidity using NXP’s MPL3115A2 and Honeywell’s HIH7120 ICs. Using these sensors, air leaks can be detected by looking for fast, abnormal changes in the hull’s internal environment.
This board allows the TX2 to connect to a CAN bus for interfacing with the ESCs and embedded systems, using the MCP2562 transceiver. It also provides i2c busses for connecting to sensors, such as Blue Robotics’ 300m depth sensor.
Hydrophone Signal Conditioning Board
Before the signals provided by the Teledyne TC4013 hydrophones can be processed by the signal signal processor, they need to be amplified, filtered, and DC biased. The board uses Analog Devices’ AD8336 variable gain amplifier, the LTC1264 switched-capacitor filter, and variations of the LTC624x op-amp for voltage buffering and amplitude clipping. A custom designed, +/-5V, dual-rail, on-board power supply is used to allow for pure AC amplification and filtering.