St. George's Robotics Team Autonomous Underwater Vehicle
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St. George’s Robotics Team Autonomous Underwater Vehicle Spencer Chan Calvin Cheng Stanley Cho Evan Johnson Spencer Louie Ezaan Mangalji Giulio Rossi Marcus Tan Kevin Tian Raymond Wang Carl Xi Leon Zhou AUVSI Foundation and ONR’s 16th International RoboSub Competition SSC Pacific TRANSDEC, San Diego, CA July 22–28, 2013 Abstract Following a successful showing at the 2009 AUVSI RoboSub Competition, the St. George’s Robotics Team has built a new autonomous underwater vehicle from scratch, which it is proud to enter into 2013 competition. The design of the robot is built around the general architecture of a dirigible airship; the main computer and batteries are located in a long cylindrical tube, with the “gondola” section of the robot housing the thrusters and propulsion system. The sensors attached to the system include an accelerometer, a gyroscope, a compass, a pressure (depth) sensor, and a Hall effect sensor, which will work in coordination with a Dreamplug computer to control the movement and direction of the AUV. Needless to say, the robot this year is merely a skeleton of what the team hopes to accom- plish in the upcoming years; the plan for competition this year will be more of a learning experience to see what can be improved upon in the future, in terms of both hardware and software. This is also the first time competing in the RoboSub competition for all of the team members; regardless, despite the lack of experience, the team hopes to remain competitive in the field with this autonomous underwater vehicle, which has taken the team three years to meticulously build and put together. 2013RoboSubCompetition JournalPaper 1 Introduction resulting in a much lengthier time required to construct this AUV. Build sessions have 1.1 Team Background typically occurred on Sunday afternoons, af- ter school on weekdays, and during holiday St. George’s School is a high school located breaks. in Vancouver, BC. Although the school is known for its myriad athletic, artistic, and The robotics team is divided roughly into academic pursuits, one area from which lit- three general groups. One part of the team tle is often heard is its robotics program. In focuses on the mechanical aspects of the 2009, the St. George’s Robotics team com- robot, using lathes, drill presses, and saws peted in the RoboSub Competition for the among other tools in order to craft the va- first time in school history, finishing 17th in riety of pieces required for this complex ma- the competition, and earning the “Best New chine. The second group, the programmers, Team” award. As the participants in compe- work intensely with the sensors and the com- tition are primarily prestigious universities, puter in order to create an interface that will this finish was quite an accomplishment for allow the robot to complete the course with the Saints team. the least margin of error possible. Robotics at St. George’s has always ex- Finally, a number of members work on isted an entirely extra-curricular endeavour; communicating information, not only be- the members of the robotics team do re- tween the former two groups, but to the search, plan collaboratively, and construct general public as to the progress of the the robot all outside of class time. The team robot. This group comprises the photog- that is participating in the competition this raphers, video producers, website designers, year is a completely new crew from the 2009 and report writers. Needless to say, cooper- team, as all of the members of the former ation between these groups was essential to team have graduated. The robot has also the success of the robot, so the team was very been built entirely from scratch: the philos- fortunate to comprise members who were so ophy of the team is that once all the members willing to work together to ensure that the who took part in the initial construction of AUV was built as efficiently and economi- the robot have departed, that robot must be cally as possible. retired. This current robot has taken three years to 1.2 Robot Design finally take shape. Unlike a number of other This AUV is based of the general structure teams in the competition, the St. George’s of a standard dirigible airship. Though the Robotics team runs on a very restricted bud- base elements were inspired by the robot get; the funding to the robotics program crafted by the team of 2009, a number of im- has been fairly limited over the past few provements have been added to address the years. As a result, the team has opted to shortcomings of the previous design. save money over time as much as possible, The main systems are housed inside a St. George’s Robotics Team 1 2013RoboSubCompetition JournalPaper cylindrical acrylic tube, inside which the bat- knowledgeable about the design rationale be- tery compartments and main computer are hind most of the decisions made during the stored. At one end of the tube is the com- construction of this AUV, the team also pass, and at the other end, an aluminium hopes to gain points simply through their end cap to dissipate the heat generated by knowledge of the inner workings of the robot the computer within the module. during the static judging stage. Waterproof wires lead from the end cap into a thruster under an aluminium frame 2 Hardware suspended under the main tube. This thruster turns a brass rod, which is attached The hardware aspect of the AUV can be to a worm gear. As the worm gear con- roughly categorized into two main sections: nects to the thrusters on either side of the the mechanical portion, which includes all of robot, sending a signal to power the central the metals, plastics, and other materials used thruster (which results in the revolution of to construct the skeleton of the robot, and the worm gear) will cause the vertical an- the electrical portion, which comprises all gle of the forward thrusters on either side to of the onboard sensors, computers, and con- change. This is how the depth of the robot trollers used to navigate the AUV through- will be controlled; the powering of the two out the course. thrusters on either side when they are tilted upwards will cause the AUV to rise, and tilt- 2.1 Mechanical ing them downwards will cause the opposite The major mechanical parts of the AUVthe to occur. battery compartments and the computerare enclosed in the main housing. Below the 1.3 Mission Strategy main housing lie the parts needed for the op- The principal goal this year is fairly sim- eration of the three thrusters, which are used ple: to pass through the validation gate, fol- to control the propulsion and orientation of low the path, and finish up at the traffic the robot. light buoys. Based on the limited equip- ment/sensors available on board the AUV 2.1.1 Hull this year, this seems to be the most realis- The central components of the robot are tic estimate of the number of tasks that can housed inside an acrylic cylindrical tube, 3 be completed. feet in length with an 5.25-inch inner di- Although the number of tasks completed ameter and a 5.5-inch outer diameter. The seems to be small, the team also hopes to team opted for acrylic primarily because the gain a number of points via subjective mea- material is transparent, making more appar- sures, such as the quality of the team web- ent any leaks and any other issues issues in site, journal paper, and introductory video. the water. Acrylic is also quite durable, an Because every member of the team is quite important quality considering that the tube St. George’s Robotics Team 2 2013RoboSubCompetition JournalPaper houses the most critical parts of the robot. batteries (1.2V each) in series was decided The end cap of the tube is crafted from upon, to ensure that sufficient power was aluminium, selected for its heat conductivity available to the robot. A lathe was used to and malleability. These properties reduced machine the half-inch sheet of acrylic into a the time required to machine the end cap circle, just enough for it to friction-fit into down to size and made it easier to fit the O- the cylindrical housing. Indents were drilled rings and waterproof wires into the end cap; at various points into the acrylic to fit brass furthermore, they allow for effective heat dis- rods—these rods would be used to connect sapation away from the computer mounted the two ends the battery holder, eventually to the end cap during the actual operation compressing the batteries within. of the robot. Arelativelylargeholewasalsodrilledinto Below the cylindrical tube is an aluminium the top of the material where no batteries frame which was used to hold the thrusters would be placed, for two reasons. The hole in place. Again, aluminium was chosen due lessens the weight of the robot, an impor- to its durability and relatively low cost. Be- tant consideration as the weight of the robot cause the frame will be immersed in water, is factored in during the competition. In ad- the frame was anodized to prevent corrosion dition, as the battery holder spans the entire and to increase surface hardness. In order to interior width of the central housing, space prevent the aluminium frame from scratch- was needed for the wires to pass through; the ing the acrylic tube, a foam cushion lies in hole accomplishes just that. between the frame and the tube. The foam was coated in fiberglass, to prevent the foam 2.1.3 Thrusters from chipping away in transport and to pre- The thrusters took perhaps serve its form when submerged.