Set apart from the everyday foottraffic on Stanger Street is a large gray metal door that reads “Virginia Tech: Human Powered Submarine.” Push it ajar, step over the basement threshold, and you’ve now entered the Sub Lab, inhabited by the last remnants of a coalition of super-villain engineers working tirelessly to create a submarine of diabolical capabilities. In reality, it’s a friendly, easy-going family that meets to dream up underwater vehicles. But it’s easy to let your imagination wander when it comes to submarine design, especially with the project goals that the team has in the works for Phantom 7.
Virginia Tech’s Human Powered Submarine team (VT HPS) has its eyes on the prize again. This time, the team hopes to double down on a single-pilot submarine design and take both the Fastest Submarine award and the Innovation prize home to mom. For those who have never heard of the Human Powered Submarine team before, the team designs, constructs, and tests a new submarine for competition in the International Submarine Competition Races (ISR) which occurs biennially at the Naval Surface Warfare Center in Bethesda, Maryland. What makes the competition unique is that each team must design its submarine to use power supplied by its pilot(s) to propel the submarine.
The VT HPS team already has a proven track record, having won third place in Innovation in 2009 and first place in Innovation this past June. They accomplished this feat with the novel two-man side-by-side design of Phantom 6, an interior layout that, up until then, had never been attempted. Phantom 6 implemented a linear drive train (LDT) consisting of two sets of two pedals (a pair of pedals for each pilot) arranged side-by-side. The pilots input power into this system much like one would on a stair climber machine at a gym. The difference is that the pilots lie horizontally on their stomachs in the submarine. These two different power inputs are combined via a differential, or a gearbox assembly, allowing the combination of two collinear shafts which permit one shaft to turn faster than the other while still delivering a unified power output to the propellers. To get a sense of the differential’s importance to the design of the propulsion system, without it, the propellers would turn at different rates because the two pilots are not capable of inputting the same power for a given length of time. This makes a straight-line trajectory nearly impossible.
Another innovation employed in Phantom 6 is its electronic system consisting of a data acquisition system and an LCD heads-up display. Because of the addition of various sensors to the body of the submarine, its roll, pitch, yaw, speed, RPM, and depth can all be measured and displayed to the pilots in real time on an LCD screen within the submarine. Not only is this an invaluable tool for the pilots during competition, but it also served the team well during pilot selection. By recording this data on an SD card during the testing of Phantom 6, the performance of different combinations of pilots could be compared afterward to determine the optimal crew for competition, as well as recording data for future submarine design.
When asked to discuss the major design innovation goals for Phantom 7, Brian Cain, president of VT HPS, replied, “Phantom Six was obviously successful in the innovation category, but not so much with speed, and that’s to be expected from a submarine her size. But what we’re trying to do with Phantom 7 is, now that we’ve proven that we can waterproof the electronics and that the system actually reads accurately, we want to try and put an electronic control system on it. [This would consist of] an electronic joystick that the pilot can manually operate, but could also have an auto pilot mode to make us go straight during competition. That way all we would need to focus on is pedaling; we wouldn’t have to focus on steering the sub, which would be really important to the psychology of the [pilot]. Eliminating one of the biggest thought processes you have to do underwater would be huge for speed.”
From this response, it’s apparent that innovation is not the only item on HPS’s laundry list of design considerations. The ISR competition is a race after all. Brian went on to say, “The other thing we are trying to do is go back to a single-person design and volume optimize Phantom 7 so we can go really fast. We saw that (human-powered) subs can reach up to seven knots, so we want to try and make that.”
However, the team is not shying away from its tradition of innovative solutions either. As Brian mentioned, one huge design aspiration for Phantom 7 is to equip it with an electronic control system, perhaps even an auto pilot mode. The propulsion sub-team is also investigating the implementation of a propeller, the pitch angle of which could be varied with increasing speed by the proposed electronic control system. This would allow the submarine to generate the maximum power and thrust at a given speed, allowing faster acceleration and reduced performance deficiencies resulting from off-design operating conditions. While the LDT will likely reappear in Phantom 7 for the simple fact that “we know how to build it and we know it works,” according to Brian, it may be augmented with a continuous variable transmission (CVT). This allows the change of gear ratios without the discrete jumps from gear-to-gear exhibited in a car or bike transmission. It “continuously varies” these ratios, which would produce benefits similar to those of the variable pitch propeller concept.
Clearly, ambitions are high. With lessons learned from the design of Phantom 6, HPS is taking a “systems approach to design,” as Brian put it. In so doing, the hope is to create more communication and collaboration between sub-system teams within HPS resulting in a better overall submarine. With this approach, if HPS successfully implements a fraction of these design concepts in Phantom 7, the 2015 ISR competition should not be overlooked.
Author, Ben Gingras, is a freshman in General Engineering. This article was first published in the November 2013 issue of Engineers’ Forum.