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Resurfacing System Design Concepts

             After deciding that the robot store all data collected during a mission rather than transmit it group 6 immediately determined that some manner of resurfacing system would be necessary to unsure that the robot would return to the surface after exiting the cave system so that it could be easily retrieved. Below is a list of several of the designs that were considered as well as the decision matrix that was used. The categories of controllability and reliability relate to how accurate each mechanism could be triggered and how likely it would be to suffer some form mechanical failure respectively.

• Weight Release- releasing weight to create positive buoyancy in order to make our product resurface
• CO2 Bladder- internal CO2 cartridge with time/pressure release to force product to resurface.
• Dissolvable Ballast- Dissolvable Ballast, in which after dissolving the product will resurface
• Expandable Housing- Spring loaded mechanism that forces the housing to expand (similar to an accordion or RV) without taking on water
• Alka-Seltzer Bladder- similar to CO2 bladder just using Alka-Seltzer tablets and water to create the gas
   

            Based on this analysis the team decided to use a bladder that would be inflated using carbon dioxide. Originally, the system was to be composed of a bladder, or a thick walled balloon, a small carbon dioxide cartridge, a solenoid valve, a pressure transducer, battery, and a simple electrical circuit. The resurfacing system would have been designed such that upon rising to predetermined depth (15 feet for example) the electrical circuit would use the pressure transducer to detect that the robot had risen to an area of shallow water that was outside the cave system. It would then activate the solenoid valve which would open to allow the gas from the cartridge to inflate bladder. The resulting increase in buoyancy would drive the robot to the surface of the water. This system would have also used a somewhat large, brightly colored bladder that would have been placed on the outside of the housing so that after it had been inflated it could serve as visual locator to aid in the retrieval of the robot.

This system has changed little since its conception with the sole changes being that the pressure transducer was replaced with a solar panel and that some of the components for the resurfacing system are shared with the buoyancy system. The decision to change to a solar panel was made do to problems with finding a low cost pressure transducer and concerns that it might be triggered prematurely by pressure fluctuations or by passing through a very shallow section of the underwater cave system. With the solar panel the resurfacing system would only be triggered after the solar panel had been exposed to significant amount of light, an event that could only happen after the robot had exited the cave system. The main drawback of this modification is that it would require that at least part of the robots housing be made of transparent material as the solar panel could not placed on the outside of the housing since that would subject it to a very high risk of being damaged or torn away rocks within the caves. With the addition of the buoyancy system that will be discussed below, it was deemed more practical to use the same carbon dioxide source and electrical control circuit for both systems.