Subsystem & Systems Level Build, Test, Integrate
Table of Contents
Completion of Head and Tail pieces
The acrylic and polycarbonate head and tail pieces were finished being built during this phase, and the box was completely assembled, the remaining penetration holes drilled, the lines and fittings connected, and the corners of the box sealed. Pictures of machining, waterjetting, the assembly steps, and the assembled fish are shown below.
A softer gasket materials was given to us by Team P14254, the Boeing Underwater Thermoelectric Power Generation team. This gasket was cut to the size of the lid, and the original red silicone based rubber (SBR) gasket was then used as a tail, as it was compliant enough to make for a good tail.
After attaching the body and tail struts, the overall profile of the fish was complete except for the skin and skin support. The struts were attached to the body and tail with Velcro, as this was convenient, inexpensive, and provided a built-in fail-safe. Should the fish be picked up in a way that might damage the struts or another part, the nose strut or other point of application will pop off instead of cracking or breaking. Pictures at this stage are shown below.
Body Shell Construction
For the fish body, it was decided to pursue an outer shell that would be split into two sections. Since the head is one solid piece that doesn't have to flex, a rigid shell will be pursued for this portion to allow greater artistic detail to be applied for enhanced realism. The shell will be constructed of fiberglass, and the existing acrylic struts will be used to mount and support the shell. In addition to the acrylic, dry foam was carved and applied to provide the desired profile. The result was a foam mold that will be used to construct the shell.
The rest of the fish covering was chosen to be the silicone treated fabric based on the results of our prior testing. A larger sample of the Spandex/Lyrca blend tested was purchased, and the EcoFlex 30 was applied liberally to coat the entire surface. From here a template was constructed using the CAD model for critical dimensions, which was then transferred onto the fabric and used to cut out the desired profile. The profile was cut to allow approximately 10-20% strain upon closure at the seam.
The skin was then fitted to the tail section to make an initial assessment of whether or not a substructure would be needed to support the skin between the ribs to stop the body from appearing bulbous around the struts.
As you can see, the struts protrude through the skin a fair amount, even with this low of a stretch (10-20%). Therefore, the decision was made to pursue a substructure to prevent this sagging. Initial attempts to remedy this issue will be completed using readily available low-grade wire mesh. To gain a further sense of any design changes that would be needed going forward, the skin was mounted to the entire body for a test fit.
The side body supports were not installed for this test fit, however even with the side supports mounted, it was clear the body of the fish needed significantly more attention. First, the box lid overhang needs to be addressed, the extra material that was left on for possibly adding more lid mounts for waterproofing, and is protruding through the skin. In order to remedy this, a similar plan of action will be employed as with the tail. The only difference will be that since the entire front half of the fish is allowed to be rigid, the fiberglass shell constructed will house not only the head, but the entire front half of the fish. This will allow placement of other features, such as fins, and a paintable surface from which we can enhance realism.
This preliminary build and test fit of the skin and body structure methods has proved our design is capable of "looking like a fish". We strongly believe that a combination of a wire mesh substructure to eliminate bulging in the tail, and a fiberglass shell encasing the entire front half of the fish for added realism will produce a very lifelike outer structure.
Electrical System and Wireless Communication
Controlling the fish wirelessly was considered an "extra" for the project, but was added into the project after some proof of concept testing. A member of the SMART Lab was using an XBee wireless transceiver to communicate with a quadcopter, so we tested the signal strength of the module by trying to block the signal by putting it within the fish body, under jackets, in tinfoil, etc. The XBee performed very well, and the results can be seen here. A friend's Bluetooth module was interfaced with the fish's Arduino, and tested during system functionality. Another Bluetooth module was also bought that is capable of not only communicating, but also programming the Arduino wirelessly, called a Bluefruit.
A substantial amount of work was also put into the electrical system aside from the wireless communication. In order to reduce the size required by the circuitry, the Power Driver shield for the solenoids was broken down and its MOSFETs were incorporated into a breadboard that fit perfectly on top of the larger of the two lipo batteries. The wiring was also completed with a section of ribbon cable passing through the electronics compartment into the lower pump area to keep loose wires to a minimum, and a 25-pin connector placed in the wiring so that the electronics tray could be disconnected from the main box. Several switches were also added in order to be able to manually control the power to the Arduino, Bluetooth module, solenoids, and pump. The wire tips were also coated with solder to keep them from pulling out of the breadboard.
The solenoid's old gasket material had also dried out, so a new one was fabricated from thin gasket material that was on-hand within the department.
Integrated System Testing
At the conclusion of this three-week phase, the project was able to be tested in the water for waterproofness and for overall functionality. The lid/box interface was found to be waterproof with the help of the new softer gasket material, and the box had a center of gravity that was much lower than the center of buoyancy, making the box sit pretty well right-side-up in the water.
System Testing Video
The test for functionality culminated in an infomercial for P14029 Systems' Bass Pro 3.2. This can be viewed on Youtube.
Updated Problem Tracking and Project Plan
Throughout the build and test process, there have been numerous unforeseen problems that needed to be addressed in a timely fashion to ensure progress didn't suffer. These problems were solved using the six step method outlined in the preparatory section of the MSD II phase. The active problem tracking document is maintained in the "Master Management Document" as a separate spreadsheet, for which the link can be found in the previous section. A screenshot of the updated problem tracking list (now on rev. 3) is given below:
Even with adequate problem solving and tracking protocol in place, the problems faced still inevitably affected the project timeline to some extent. The project plan has been updated to reflect the current timeline after overcoming all problems faced. The entire active document can be viewed here.
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|Subsystem Level Prep||Subsystem Level Build & Test||Subsystem & System Level Build, Test, Integrate||Systems Level Build, Test, Integrate||Verification & Demonstration of Results|
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