Sub-Pages

Buoyancy System Design Concepts

          The buoyancy system is responsible for controlling how fast the robot rises and falls in the water column as well as its orientation. Originally the robot was to rely on a static buoyancy system to keep the robot neutrally buoyant. This neutrally buoyant state was to be created by using an oversized housing and carefully calibrated weights spread throughout the housing. This method was discarded after concerns were voiced by the team’s instructor and sponsor about the difficulty of achieving static buoyancy and that if a dynamic buoyancy system was used the robot would have some ability to free itself from eddy currents that could otherwise trap the robot and prevent it from exiting the cave system.

            It was decided that since a compressed carbon dioxide system would be used to power the resurfacing system the same approach would be used for the buoyancy system. The addition of the dynamic buoyancy system greatly increased the complexity of the entire system as it necessitated adding a number of solenoid valves and a more complicated control system than was originally intended. The dynamic buoyancy system was originally designed to use a bladder, two solenoid valves, an electronic control system, and a reservoir of pressurized carbon dioxide. Group 6 considered replacing the bladder with a spring loaded piston cylinder that could be filled with air from one end and left open to the water at the other but it was felt that the increased complexity of this design outweighed any potential benefits. In order to keep the system as simple as possible it was decided to have the robot’s buoyancy oscillate about neutral buoyancy.

            The original oscillating buoyancy system was designed so that a simple timing circuit could alternately open and close one of two solenoid valves that would inflate a deflate bladder by allowing pressurized carbon dioxide gas into it from a reservoir or by allowing air to escape through a pipe that opened into the water surrounding the robot. The carbon dioxide was to be provided by a number of disposable, single use cartridges that would be attached to a custom made manifold in order to provide enough volume to carry a full mission.

            This simple system was modified to use a bladder, three solenoid valves, a one-way valve, and a microcontroller and single, large carbon dioxide tank that would both be shared with the resurfacing system. The three solenoid valves could be replaced by a single 4-way solenoid valve, however none could be found that would fit within the housing. The solenoids are used in conjunction with each other to control how much air is in bladder at any given time. Two of the solenoids act as a type of airlock to control exactly how much carbon dioxide is allowed to enter the bladder at a time and the third is used to the allow air in the bladder out through the one-way valve and into the surrounding water. As both systems would require similar components it was decided to allow the buoyancy and resurfacing systems to share the carbon dioxide tank and microcontroller in order to save space and money. The solenoid valves, carbon dioxide tank, one-way valve, and bladder were all connected using copper tubing. Copper tubing was used since fittings and adapters are more easily attached to it rather than plastic tubing; copper tubing is also more pressure and temperature resistant than plastic, both very desirable qualities when working with highly pressurized gas.