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Final Buoyancy System Design

The buoyancy system was the first design the team had to develop. The buoyancy system was dependent on the properties of water, being that the robot was not self propelled. Therefore the robot was dependent on the water to travel safely through the cave system. This caused the team to have to consider two separate areas for the buoyancy system. The first was coming up with a design which allowed the robot to be approximately neutrally buoyant to slightly negatively buoyant in the water when it was not operating. This was the static buoyancy system. The next system which was named the alternating buoyancy system, was to come up with a system that allowed the robot to change its’ buoyancy while it was floating through the water. The reason for this was the possibility of the robot getting stuck in a rock formation was of a high likelihood, so the robot had to have a counter mechanism.

The static buoyancy was calculated using buoyancy calculations. Determining the buoyancy of an object is dependent on the weight of the object and the density of the fluid it is displacing. This allowed the team to calculate the maximum allowable mass of the robot (Appendix B). The mass was found by multiplying the density of the water times the volume of water displaced. The team therefore needed to over design the housing to allow for the maximum displacement of water. The team initially chose to use a 6” diameter PVC housing after calculating the initial mass of the robot using some of the available components. After several failed attempts at finding the proper housing, the team decided to use a 4” diameter housing with a length of 15”. Using two of these PVC pipes gave the robot 18.8lbs of allowable mass. This would turn out to be insufficient so the team went with three 4” diameter PVC pipes to give the final allowable mass of the robot to 27.5lbs. With a final mass of 22 lbs for the submersible robot, the team was left with 5.5lbs of mass in which to use for a sensor package. A more thorough description of the housing will be discussed in the housing section.

The alternating buoyancy system was a more complicated design than the static buoyancy system. This led to several initial designs that were later scrapped. The final design used a 12 oz carbon dioxide canister which released carbon dioxide that was used to fill an air bladder which then displaced water. This creates positive buoyancy by displacing the denser water with a less dense fluid. The system operates by regulating the flow of carbon dioxide through a system of copper tubing and valves. Using a programmable microcontroller and three solenoid valves, the team is able to control the opening and closing of solenoid valves using electricity. The solenoid valves turn the electrical power into mechanical power and allow the carbon dioxide gas to pass through the valve as long as power is applied to them. The carbon dioxide is controlled using a multistage system. Solenoid valves 1 and 2 act as airlocks to allow precisely measured amounts of carbon dioxide to enter the buoyancy bladder and allow it to inflate. Solenoid valve three acts is used to vent the carbon dioxide form the bladder out into the surrounding water. Lastly, solenoid valve 4 is used to inflate the resurfacing bladder. Below is a flow chart that demonstrates how the parts used in the buoyancy system are connected.