Progress Report - Mechanical Design (01/24/2012)

     The development of the vehicle has continued to progress. After several hours of research and speaking with salespeople from a couple suppliers of paintball tanks, regulators, etc., it was determined that compressed air should be used instead of CO2 for several reasons:

(1) The outlet pressure of CO2 is a strong function of the operating temperature, and is thus difficult to predict/regulate. In fact, paintball CO2 tanks don't come with a regulator, while all paintball compressed air tanks come with a regulator already installed as a standard. Apparently the ability to regulate compressed air much better than CO2 is the reason why higher-quality paintball guns and more experienced paintball players use compressed air instead of CO2.

(2) Originally it was thought that CO2 tanks would be far more compact than compressed air tanks, however, this is not necessarily the case. There are compressed air tanks that are just as compact as compressed CO2 tanks (as I have found by shopping online). This discovery eliminates the issue of dimensional constraints.

(3) After a few phone calls, I was able speak to a supplier in northern California who had a very versatile selection of regulators, adapters, etc. In fact, they had a low-pressure regulator that can be directly attached to the tank regulator, and that also has the exact desired threaded outlet (i.e. 1/8" FNPT), thus culminating in a compact, efficient, reliable completion to the gas distribution circuit.

*Note: The compressed air tank (with the tank regulator) and the low pressure regulator (both the tank regulator and the low-pressure regulator (required to drop the pressure down from about 850 psi to 100 psi) have analog gauges installed on them) have been ordered and will arrive shortly.

Furthermore, I developed an efficient design for the compressed air tank mount, which will be machined using the lathe and drill press tomorrow morning (relatively easy to manufacture, and the stock has already been selected).

In addition, a mounting plate for the pressure transducer has been water cut, and I picked up the one-way check valves from Grainger and successfully installed/tested them on the exhaust outlets of the two torpedo launcher air cylinders, as well as on the outlet of the exit solenoid valve for the grasp/release mechanism.

Tomorrow afternoon (when the McMaster-Carr order arrives), I will carry out my improvised modification to the camera enclosures and perform another water tight test (hopefully my strategy will work--I am optimistic as it seems like a good approach). This strategy involves adhering 3/8" thick EPDM rubber (i.e. the same material used for the gaskets) to the bottom surface of the top camera enclosure, and the top surface of the bottom camera enclosure, allowing the neoprene sealing washers, bolts, and threaded rod to pass through clearance holes. The EPDM rubber will be adhered to the aforementioned surfaces using the gasket adhesive (very strong). Thereafter, I will cleanly apply caulking around the four edges of the exposed surface of each of the two rubber pads. Then, I will pour epoxy into each of the six total exposed holes. This should prevent any leakage through the bolt threads, sealing washers, etc., as was the issue earlier. Furthermore, an appropriate tape (specifically for smooth surfaces such as acrylic) was purchased in a recent order. This tape will be placed along the outer edges of the enclosures in a clean fashion such that all the caulked edges will have this extra layer of protection. The final outcome should hopefully be more reliable (i.e. water tight), aesthetically-appealing camera enclosures.

I also made another (hopefully final) McMaster-Carr order this evening, which includes an assortment of items such as another NPT adapter, a liquid rubber wire-protecting agent, heat shrink tubing (with an internal adhesive to assist in preventing water from coming into contact with the soldered wires), a 5/16" thick sheet of acrylic (to be used for the hydrophones mount, as well as to complete the pressure transducer mount), and a few small neodymium magnets which I hope to use on the revised versions of the torpedoes which were 3D printed late this afternoon, and will be retrieved tomorrow morning for surgery (i.e. I need to drill into and install a stainless steel rod at a specific depth--similar to the initial version). The small neodymium magnets were chosen for their compactness due to their high magnetic field/volume ratio, and should provide an even cleaner design than with the bar magnets. Also, this slight revision is being done because I forgot to factor in the addition of the magnet when performing my calculations, and thus the center of buoyancy deviated from the original center of mass, thus yielding torpedoes that tilted back slightly when submerged underwater. This negatively affected their hydrodynamics, and after removing the magnet from one of the torpedoes, the density was perfect, the center of mass and buoyancy were great, and the torpedo moved nicely through the water. The necessary adjustments are being made to the second generation of torpedoes.

I also discovered on Monday that the SEACON connectors will arrive in the first week of February as the order was unfortunately not completely processed until January 6th (despite being submitted prior to winter break). This is okay, though, as there are still other productive tasks that can be completed until then. In addition, the pressure transducer will be ordered on Friday (W-9 forms were not supplied by the company, so the order had to be cancelled, and it will need to instead be ordered out of pocket), and two more SQ26 hydrophones will be purchased by the end of the week (the two from last year were determined to work fine for the frequency range required, and I spoke to branch of the company in Seattle, where I was provided a quote and also made aware of the availability of these hydrophones.

Furthermore, the solenoid valves were successfully tested today, and my proposed circuit will work. I will have Hang help me make a PCB containing four of these identical circuits shortly.

                       -Eric Sloan (ME Project Manager - AUVSI Robosub Competition)