Systems Level Build, Test, Integrate
Fiberglass Shell Construction
The front half of the fish was designed to be covered with a fiberglass shell. The profile of the head of the fish was made with green floral foam, and then the fish body was covered with a wire mesh and plastic garbage bag in order to protect the fish and keep the resin from dripping onto it. Mold release and then chopped fiberglass mat and slow-hardening resin were applied to the plastic bag, taking care to keep the entire soft structure from sagging. After curing, the fish was pulled out from the fiberglass casting, sliding the fish and wire mesh out of the plastic bag before removing the bag. A Dremel was then used to trim the bottom of the shell, and Bondo body filler was used to smooth out any uneven contours, and additionally build up features such as gill plates, eyes, pectoral fins, and upper jaw cartilage for added realism. Pictures of construction and the shell before painting are shown below, finishing with placing the shell and skin on the fish.
Shell PaintingIn order to aid in the aesthetic authenticity of the robot, a lifelike paint job was key. The grey primer used to seal the shell wasn't doing a very good job of that, so inspiration was drawn from native freshwater species. The largemouth bass served as a reference point, a native species to our area, and the colors green, white, gold, and black were picked to mimic the fish's appearance.
Traditional aerosol spray cans were used for this project to keep costs down, and simple blending techniques outlined in many hobbyist forums online were used to produce the desired effect. To paint in finishing touches, a small mixable color pallet was bought from a hobby store to custom blend colors for the eyes and fins. Finally, a thick layer of clear sprayable RTV was used as a finish coat, which serves not only to protect the paint from chipping, but also added a gloss that gave the fish a "wet" look out of water while making it feel softer to the touch as an authentic fish would.
Solenoid FilterDuring initial testing, a piece of dirt or other small debris was able to plug one of the solenoid valves, so a filter was made in order to prevent this from happening again. Fine brass filter mesh was obtained from Dr. Steven Day, and this was soldered to a brass pipe fitting and screwed over the end of the inlet port.
The rubber gasket was left out when screwing the lid down at one point, and without the soft cushion that it provided, the polycarbonate lid cracked most of the way through. The decision was made to machine a new lid, and to switch to aluminum with a polycarbonate viewing window. This design change made the lid much more robust, while keeping the ability to view the electronics. The gasket was then glued to the bottom of the new lid, to make for faster assembly and to avoid leaving it off again.
The enclosure for the pump and electronics components was found to be waterproof upon construction, but the bonds between the pieces of the box quickly began to weaken and permit leaking. This was solved by using stronger glue, simply cyanoacrylate superglue instead of the contact adhesive purchased from McMaster-Carr. All the components were removed from box, the silicone caulk was removed, and superglue was applied around the edges and allowed to wick into the joints. Fortunately, this didn't require completely disassembling and reassembling the box.
The first round of testing in the RIT swimming pool showed that the Bluetooth module (Adafruit's "Bluefruit" module) was having difficulty communicating wirelessly when submerged, so testing was done in the sink in an attempt to quantify this. It was found that the signal attenuated rapidly the further the module was below the surface of the water. At ten inches below the surface, the attenuation increased the upload time to a couple minutes and would sometimes fail, but as long as the box was partially above the surface, uploading was done in a matter of seconds.
Buoyancy ModificationsThe addition of the shell made of fiberglass and body-filler helped cancel the problem of the fish being tail-heavy; that is, weighing down the front of the fish made it float closer to level instead of nose-up. Unfortunately, this raised the center of gravity above the center of buoyancy, to the point where the fish would tend to float on its side, and required the use of foam in the top of the head and weight at the bottom in order to correct this.
ASME Student Robot and Mechanism Design Competition
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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