Functional DecompositionA top-down functional decomposition was performed on the robotic fish concept, down to the level subject to brainstorming. From here, the functional decomposition transitions to the morphological chart.
A morphological chart was made summarizing the different options for each function. This included everything from the locomotion style to specific physical components.
Systems ArchitectureBreaking the system into smaller subsystems enabled modularizing the design, and determining the relations between the interconnected system components. The system breakdown is shown below at a high level, followed by a more detailed treatment.
Feasibility AnalysisThe feasibility analysis was a subset of the total engineering analysis, and was done in order to make an informed decision between the two leading concepts. The first step was to determine what analysis to perform, based on the total engineering analysis picture. Both started with an estimation for the required flow rate.
Concept 1: Centrifugal Pump and Solenoid ManifoldConcept 1 is an untethered salmon body type, using a centrifugal pump to pressurize water and a solenoid manifold to distribute it to the muscles, and the engineering analysis that it would entail is shown below.
The equipment necessary to implement the Centrifugal Pump and Solenoid concept for the fluid pressurization and control system is shown below as well as the cost breakdown. The selected pump, it's flow curve, and the selected solenoid valves are also shown. The pump runs on 24 Volts DC, in keeping with the safety specifications established for exposed voltage, with a maximum current usage of 3.6 Amps at full flow. It has a static head of 21 psi, and a maximum flow rate of 5.3 gallons per minute.
Power Consumption AnalysisOne concern regarding the untethered centrifugal pump concept was power consumption, as it would require bigger and heavier batteries. The power consumption for a worst case scenario is given below, where the pump is at maximum flow rate. This is an overestimation because the maximum flow rate won't be reached (and pumps consume less power if they're imparting less energy to the working fluid), and the pump is variable speed.
Buoyancy AnalysisThis is followed by preliminary buoyancy analysis, assuming that 50% of the body segment (the frontmost portion of the fish) is able to be filled with air for floatation purposes. This is compared against the weight of the selected pump, and a 4 Amp-Hour Lithium Polymer (LiPo) battery capable of powering the system for a minimum of one hour under worst-case power consumption conditions.
Note that the cost estimation is for the Pressurization System only, not the entire fish
Concept 2: Syringe Pumps Powered by ServomotorsConcept 2 is also an untethered salmon body type, with syringes to move the fluid to the muscles and waterproof servomotors actuate the syringes, and the engineering analysis that it would entail is also shown.
The equipment and cost of implementing the Syringe Pump and Servomotor Concept are shown below. The servomotors are high-torque, rated for 179 oz-in, and are not continuous but have a range of motion of 180°. The moving ends of the syringes are attached to the moving portion of the motor with minimum linkage. As illustrated in the preliminary Solidworks drawing, rotating the motor pushes one syringe pump in while pulling the other out.
Note that the cost estimation is for the Pressurization System only, not the entire fish.
Concept SelectionPugh analyses were done on several aspects of the design including body styles and the pressurization system.
Concept 1, the Centrifugal Pump and Solenoid Manifold, was chosen for the Pressurization System. The final concept was therefore an untethered, two-jointed salmon, with a centrifugal pump, manifold of solenoid valves, with a soft polymer skin, and an expandable air bladder to control the buoyancy.
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