Table 1. Flexinol Wire Properties
In the current model, four wires were used per side for each actuated segment of the tail. Using the wires in parallel linearly increases the force available while retaining the ability for fast cycle times, as opposed to using large diameter wires that would require much longer times for convective cooling of the wires. The wires and any contacting electrically conducting material was covered with PlastiDip for electrical insulation from the water.
For propulsion efficiency studies, the vehicle does not possess navigational instrumentation. The testing consisted of commanded tail movements, and not of specified vehicle trajectories. In order to accomplish this, feedback control was implemented from the tail in order to determine its deflection. The actual control law itself was quite simple at this point, and was implemented on a simple MC68HC11 microprocessor. The initial control law for each set of wires is a phased full-voltage command, in order to actuate the wires sequentially along the length of the fish and achieve the travelling waveform. Eight binary output channels were required to control each set of wires, and up to eight A/D input channels. Eight binary input channels were sufficient as only the phase transition information was needed. The output channels controlled FETs for the individual wires.
The static model of the fish was defined using the variables shown in Figure 4, all defined in the tail coordinate system. The spline is divided into spline segments by vertical lines, and circles represent the pivot locations.
Centerline of Fish
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