Team Kanaloa 4 of 7

P-Type and 2 N-type transistors, allowing for the quick and reliable switching of voltage polarities; the motor controllers would only have to control speed. However, the H-Bridge is a complex and advanced circuit and proved to be difficult to build and control for high current systems. The components in the H-Bridge, the P and N type transistors, were small. This made soldering difficult as the component had small surface to solder wires to. In addition, the transistor would absorb heat quickly during soldering, potentially damaging the component. Controlling the H-Bridge had its own set of difficulties. The transistors had a low impedance on the signal side, which caused them to draw more current than the Main Arduino could handle, potentially damaging it. Resistors helped to solve this issue. Each transistor within the MOSFET H-Bridge is controlled individually using the Main Arduino. During testing using multiple transistors at once was more difficult than using a single transistor. Each transistor required multiple wires and took up a lot of space on the Arduino. The main issue with the H-Bridge was the tendency for the component to damage itself. If the transistors were incorrectly activated, then the circuit could short the battery within itself, damaging components and potentially rendering the circuit unusable. This situation happened frequently, and it was ultimately decided that the MOSFET H-Bridge would be a nonviable solution.

interruptions and pauses in I2C communication. Occasionally, while the WAMV was in operation, one of the DAC’s would be unresponsive, sending a constant 2.5V (which was half the voltage supplied to it) to the motor controllers. Multiple approaches were taken to fix this issue. On the protoboard level, much soldering work took place, either to replace a DAC that was suspected of being inoperable or to resolder a connection after a DAC was resoldered. From a system level, rewiring was the approach chosen. The initial attempt at integrating the DACs placed it into the high current box. Under the assumption that interference was affecting the SDA and SCL wires to the DACs, the DACs were moved to the low current box. The problem persisted. Review of the data sheets for the MCP4725 Breakout Boards showed that the DACs may have a certain current limitation; if the design were to be repeated, adding resistors to the power pins of the DACs would reduce the chance of the internal components breaking. Also, during the testing phase, the DACs received multiple alterations to make compatible with the motor controllers which required re-soldering and removing pins. It is also highly suspect that the DACs were damaged thermally before being soldered to the protoboard. Regardless of the possible causes, a quick, inexpensive replacement was found by passing PWM signals through a low pass filter to produce a pseudo-analog signal.

As mentioned in the high current box section, one possible option for sending analog signals from the Master Arduino is to use a Digital Analog Converter (DAC). Originally for each motor controller, the design for controlling the motor controllers was to use 1 DAC for each motor controller (4 total). The DAC’s chosen were MCP4725 Breakout Boards. These boards communicated with the Master Arduino using I2C; unfortunately, with I2C each component must have a unique address and most marketable DACs have only two configurable addresses. The solution to this issue was to employ a multiplexer, the TCA9548A I2C Multiplexer, to moderate which DAC is communicating with the main Arduino. All these components were soldered on a protoboard.

###### Figure 8: Low Current System

#### C. Kill switch system

The current kill switch system consists of a Taranis QX7 transmitter, a FrSky R9 receiver, an Arduino, two relay boards, two physical buttons on the WAM-V, and LED strip shown in Figure 10. Team Kanaloa previously used a Digi XBee radio module on an Arduino but changed to using a channel on a R9 receiver to send a kill signal to an Arduino. This change was due to the XBee having difficulty sending a signal over a distance of about 300 meters while the WAM-V is out in open waters. The Taranis QX7 transmitter paired with the FrSky R9 receiver can cover a distance just over 1 km. The operational procedure of the kill switch system is to have the Arduino monitor the state of the WAM-V via the two physical buttons attached to the WAM-V and a remote switch on the Taranis QX7 transmitter. If either of the buttons or remote switch is engaged, the Arduino sends a signal to the relay

###### Figure 7: Wiring Diagram for Digital Analog Converter

While the solution seemed simple, there were many unexpected issues that propped up during the integration phase. The most prominent issue was