Final Design

The final design of the robot exhibit utilizes a user interface where museum visitors can turn a hand wheel which causes bubbles to emit from a diffuser located at the bottom of the exhibit tank. This provides active buoyancy control for the robot, allowing it to move up and down within the tank. To accomplish this, the negatively buoyant robot rests atop the diffuser when no bubbles are being produced. When the bubbles are emitted, they accumulate in the bubble canopy, which is attached to the cylindrical robot housing. This accumulation results in an increase in volume of the whole system causing positive buoyancy. A series of small holes through the canopy allow a small amount of the bubbles to escape so that when the hand wheel is not engaged, the bubbles will flow out of the canopy and the robot will return to its resting position on the bottom of the tank. The user is encouraged to generate bubbles with the hand wheel to increase the robot's buoyancy and bring it to the water's surface in the tank so that the robot can transmit temperature, pressure, and light data it has gathered to the user when it reaches the surface. The user then will see profiles of the water in the tank for each type of data collected. In order to prevent any horizontal misalignment of the bubble canopy over the diffuser, a pair of alignment cables run from the bottom of the tank to top, passing through four eyelets on the robot. Lastly, the robot's battery will receive power from an inductive charger at the bottom of the tank, charging the robot when it is at rest.

Within the robot housing, several electronic components are utilized to collect and display data that is used in marine robotics. These include temperature and pressure sensors and the means to transmit this data to a display screen for the user to view. These data sets are important information used in the marine robotics industry for understanding more about the ocean and the life within it. By visualizing and interacting with how an underwater robot moves and collects data, visitors of any age who experience the exhibit will learn something about the interesting field of marine robotics.

In order to reduce development time and solve a number of design challenges, a Blue Robotics Cylindrical Locking Enclosure was chosen as the main body of the housing. This provides a waterproof space to store the robot's battery and microprocessor, while also having spaces on the top and bottom end caps to interact with the environment. A bottom end cap composed of thin HDPE sheets allows the receiving coil of the inductive charging system to come within range of the transmitting coil, while a top end cap composed of acrylic allows an upwards-facing UV sensor and ports for a temperature and pressure sensor, pressure relief valve, and antenna. An internal structure was created from HDPE sheets to securely and precisely mount three protoboards, a rechargeable battery, and a receiving coil. As all of the internal structure mounts to the top end cap, the electronics can be fully removed from the encasing cylinder as a unit, which lowers maintenance challenges. 

The bubble catcher, sometimes referred to as the "bubble canopy" is the means by which the robot adjusts its buoyancy. By capturing bubbles emitted by the diffuser (located on the bottom of the tank) the robot is able to ascend within the tank. If the bubbles are turned off the robot will slowly descend due to a series of air relief holes placed along the apex of the canopy.

The bubble generator consists of a hand wheel, a wheel speed sensor, a raspberry pi, and a DC aquarium aerator pumping air through a ring-shaped bubble diffuser at the bottom of the tank. The rate at which an aquarium guest spins the hand wheel controls the rate at which bubbles are generated. The raspberry pi also receives data from the robot's sensors via a radio transceiver and displays it to the user, informing them about water conditions, which demonstrates the role of marine robots in the real world.

The inductive charger provides a reliable, low maintenance way to charge the battery which powers all onboard electronics. By using wireless inductive coils, the system can charge through the housing of the robot. The system also automatically establishes a connection when coils are within range, thus allowing the battery to charge anytime the robot is resting on the bottom. In this manner, the robot can charge intermittently throughout the day, as well continuously overnight.

Given the range limitation of the inductive charger, a means to minimize misalignment is required. This is achieved through two alignment wires running veritically in the tank. The wires connect to the base plate at the bottom, and a custom adjustable mount at the top. The robot has two clips on either side to connect to the wire. When clipped on to the wire, it constrains the robots movement from 6 degrees of freedom to only the 1 in the vertical direction. The wires are standard fishing line, which is semi translucent so as to minimize their visual impact to the exhibit design.