Final Design

System Model

Key Components

Heave Plate The final design of the heave-plate was a 1.58mm thick central hexagonal plate, surrounded by six respective “petals” that were attached along the edge using marine-grade hinges. Upon the descent of the heave-plate, drag causes these “petals” to close. This mechanism decreases the projected area of the plate, which allows it to descend at a higher velocity, as the smaller area decreases the drag force acting on the plate. Once it reaches its target depth, the weight of the petals causes them to open, increasing the surface area . To prevent overextension of the petals and decrease the stress on the joints of the plate, a bottom frame was fixed to the central plate. This frame provides a surface for the petals to contact upon opening, maintaining a flat, hexagonal plane with a new, increased surface area. This larger surface area generates a larger drag force which limits upward movement of the plate when oscillating waves cause the buoy to float. Finally, the central plate is equipped with an attachment that allows the actuator to be easily fixed to the heave plate so it can easily be integrated with the rest of the system. All surfaces and hardware for the heave-plate are made of 316 stainless steel to provide sufficient mass and prevent corrosion. 

Buoy The final design for the buoy component is one constructed by the team out of expanding polyurethane foam. This allowed for full control over the shape of the buoy and customization of the cavity for the electronics housing. The shape of the bottom of the buoy is a cosine curve to maximize wave power absorption when compared to other shapes such as a conical, cap, or arc shape. While this comparison was for much larger buoy designs (15m diameter), the assumption was made that the properties would scale down to the smaller (<1m) buoy used in this design.The final buoy design also featured a square cavity compatible with the selected waterproof housing for the electronics.

Electronics Package The Arduino Mega was selected due to its expanded I/O capabilities, four hardware serial ports, and increased RAM, enabling reliable interfacing with multiple sensors. The Mega’s stable 16 MHz processor effectively handled data logging from multiple sources at 5 Hz without compromising system stability. While the ESP32 offered faster processing and wireless communication, its 3.3V logic and challenges with SPI and I²C concurrently posed compatibility issues. The Raspberry Pi provided substantial processing power but introduced unnecessary complexity with its OS-dependent structure and potential power stability concerns. Therefore, the Mega provided an optimal balance of processing power, connectivity, and simplicity for the prototype, while maintaining 5V logic compatibility with all sensors.

Waterproofing The final design for the waterproofing components was a customized housing with standard connectors. The housing on top of the buoy is a Polycase ZQ-060604 enclosure. This enclosure was customized by machining one hole through the bottom of the box for the cable gland and a smaller one beside it for the turbine wires to fit through. The cable needed to pass through the bottom of the enclosure to reduce stress when fed through the center of the buoy to connect with the heave plate below. 

The housing that sits on the heave plate is an acrylic cast Blue Robotics watertight enclosure with aluminum Blue Robotics flange caps. A Blue Robotics enclosure was chosen as it is compatible with the Blue Robotics pressure sensor the sponsor already had and is a trusted source for marine housings. A WetLink penetrator was added for the cable to pass through the end cap, as well as caps to close off the additional openings. This enclosure integrates well with the heave plate design and is large enough to hold all the current electronics with the capacity for more if needed.