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Background Information

In the beginning of this design project the Team 6 considered several initial design factors that had to be addressed.  They were as follows: whether to use many cheaper disposable designs or to use one expensive design, whether to tether the vehicle or not, whether to have a propulsion system or to allow the robot to use natural water currents for propulsion, where to retrieve the vehicle from, and finally whether to maintain constant communication with the robot or to store the data on a downloadable drive which will be retrieved with the robot.  Before the design of the primary or secondary systems the team had to decide on the initial design constraints. Several considerations had to be taken into account for each of these design constraints.  When approaching whether to use many cheaper designs or whether to use one expensive design the team considered several factors: the physical make up of the cave systems, the complexity of each design path, and the cost of the components.  Knowing that the cave systems were dangerous, with jagged rocks hanging from the ceiling and coming out of the floor the team realized that the possibility of the robot getting stuck was good.  The team also knew that the pressure on the robot would be great. Group 6 knew that at 300 ft there was about 900kPa of pressure.  In developing an expensive design, which stood a reasonable possibility of getting stuck, the team then considered how complex this design needed to be to minimize failure while in the caverns.  The teams’ backgrounds being in mechanical engineering and not electrical engineering group 6 quickly realized that developing an autonomous robot was beyond the capabilities of the group at this point.  The team also had to consider that this project has a budget and the more complex the design is made with moving or electronic parts the more expensive the project will get.  Therefore the team decided on a cheaper design that can be reproduced as required for each mission.

The next initial design constraint the team had to consider was whether to tether the robot or not.  This proved to be one of the easier choices to make.  The group knew from the information given to them by their sponsor that the submersible robot would be operating at a depth of 300ft.  Group 6 also knew that the cave systems ran for several miles in some areas and that they are dangerous to navigate. Also, any tether long enough to permit the robot travel length of the entire system would be extremely expensive. This led to the decision that it is impractical if not impossible to run a tether system throughout the cave system.

The next consideration the team had to make was whether to have the robot be self-propelled or use the water currents as a means of propulsion.  The team had to look at several key factors when making this decision.  First, size was considered; the robot is limited by the size of the cave openings.  While there are not any concrete numbers it is known that the openings are as small as 1ft by 1ft so the team must be conservative in the overall design dimensions.  Further, the team then considered a power source to run the propulsion system, including the extra cost for the required components, the component dimensions, how much power is needed to keep the system running and what kind of design would be used.  Another major problem, which would then be created by self-propulsion, is how the robot would navigate while submerged.  The team has a limited knowledge of control systems and investing too much time in this area will take away time needed in required areas.  The team therefore chose to have the robot be propelled by the water currents to minimize as many obstacles as possible.  This decision opened up another design system that was not initially considered though.

Due to the physical make up of the cave systems the robot would now need to be neutrally buoyant or it would need to mimic neutral buoyancy.  This is due to the heavy silt composition of the floor and the dangerous rugged rock make up of the ceiling.  The team then reexamined the choice for the propulsion system and decided that mimicking buoyancy was a more realistic goal than self-propulsion with all the associated problems that go with it. 

The next design consideration the team had to reflect on was where the robot would be recovered from, the entrance or some exit downstream.  The team’s decision on propulsion systems had made the choice already since the current runs downstream.  Therefore the robot would be put in at some entrance and would be retrieved downstream at some opening in the cave system. 

The final consideration the team had to make before the actual design could begin was how a communication system would work.  It was known how deep the robot would be operating in and the team knew that 300ft of bedrock and water would diminish any ability to maintain communication.  The team also knew that if they wanted to maintain constant communication with the surface a system would need to be setup above ground.  The problem with this was that no one has a good understanding of where the cave systems runs, and this set up could prove to be very expensive.  Therefore the team chose to use a system that stores data inside the robot and can be retrieved when the robot is recovered.

            Having made the initial design considerations the team was able to begin the design of the primary and secondary systems of the robot.  The team knew that due to the decisions made regarding the initial considerations the primary and secondary systems would be dependent on these choices.  The primary system became size and shape, resurfacing methods, buoyancy methods and finally a locator system.  The secondary system required was a package to sense and record information about the environment and robot.  This information is pressure, velocity, heading, and temperature.  Due to the team’s choice on the communications method a means for storing the required data after it has be been recorded also had to be found.