SubmURSA Mechanical - 2011

Mechanical Platform

This year ARVP is introducing a new autonomous robot, SubmURSA, and hence a new mechanical platform.  This platform has been designed to be as modular as possible.  Because of this, the same thread size was used for all external connections, allowing the external location of each external connection to be adjusted as necessary.  To allow for quick observation of the electrovisual signals indicating the remaining battery life and the presence of any malfunctioning boards, a clear outside shell was chosen.  Another improvement is the use of a combination of pumps and thrusters to propel SubmURSA.  The pumps increase the adjustibility of the robot and the thrusters increase the robot's speed.  One feature that has been drastically improved from the previous robot, Bearacuda, is the amount of time required to open and close the pressure hull.  It took approximately 10 minutes to seal Bearacuda, whereas SubmURSA, due to the new draw latches, can be sealed  in approximately 30 seconds.

Pressure Hull

A major portion of the new platform design which needed significant overhauling, was the pressure hull.  In the pressure hull design of SubmURSA, the areas of visibility and accessibility were the top priority, with secondary goals of modularity also being achieved.  The hull is essentially an aluminum box, with a polycarbonate lid.  To reduce the weight of the hull, the wall thickness of the aluminum sidewalls is 4mm, with a slightly thicker base, measuring in at 5mm.  Since the connectors have 20 threads per inch, this wall thickness only provides approximately 3 threads, which was deemed unsatisfactory.  To overcome this issue, special extrudes were designed with a thickness of 8mm, which are then adhered to the hull.  This allows the connectors to sit securely in the hull, without significantly increasing the mass of the hull.  Also adhered to the walls of the hull are ten mounting points for the draw latches used in the new sealing mechanism.  By manufacturing the mounting points separately, this allows for ideal placement of the latches to optimize the clamping force, and also allows for some mass reduction, since the wall thickness was not increased.

The visibility goal was achieved by the design of the clear polycarbonate lid.  As previously mentioned, this allows for quick observation of the electrovisual signals designed on the electronics boards.  The lid is created by heating a 1/16" sheet of polycarbonate, and then blowing it through an MDF frame, which allows the polycarbonate to be blown into a dome shape.  This allows for a simple and quick forming method, which allows for the manufacturing of many different lids, with different heights or colours, within a short time frame.  It also allows for the optimization of the lid shape.

Complementing the visibility of the hull, is the accessibility of the inside of the hull.  Due to the use of draw latches, the unsealing time of the hull is under a minute, which allows for quick repairs of electronics to occur, while not consuming amounts of time that could be detrimental to the internal components.  Also adding to the accessibility of the hull are two underside rails and a rail system on the main frame.  This allows for the hull to easily slide in and out of the frame so that the internal components can be accessed uninhibited by the rest of the frame.  To aid in the removal of the hull, an easy-access handle is mounted to the back of the hull, which is pulled when required.  To secure the hull while in the water, one locating clip, held by one cap screw is sufficient.

The modularity of the hull was achieved by the selection of the micro contact series of Subconn connectors.  By limiting ourselves to these connectors, and to any pin count between 2 and 8 pins, the threading of all out connectors is 7/16"-20.  As such, the external connectors can be moved around as required, and, in future years, the connector can be changed to another fitting connector to use different external components.


Also of note regarding the pressure hull, is that the inertial measurement unit has a separate case to prevent electromagnetic disturbances from other components.  A small rapid prototype case was designed and mounted onto the frame.  The case is designed to allow the IMU to fit snugly into it, while minimizing the volume in such a way as to aid in our overall buoyancy.


Plate-forme Méchanique

Cette année ARVP introduit un noveau robot autonome, SubmUrsa, donc on introduit aussi une nouvelle plate-forme méchanique.  Cette plate-forme a été conçu pour être aussi modulaire que possible.  Pour cette raison, la même taille de filetage était utilizé pour tous les connections externes, permettant le lieu de chaque connection externe d'être changé si c'est necéssaire.  Pour observé les signaux électro-visuel qui indique la vie de la pile et s'il y a des cartes de circuit qui ne fonctionnent pas rapidement, un coquille claire était choisi.  Une autre amélioration est l'utilisation d'une combination de pompes et the propulseurs.  Le robot est plus facile à conduire à cause de les pompes, et plus vite à cause de les propulseurs.  Un trait de Bearacuda qui a était améliorer est le temps qu'il prend pour sceller le coque pressurisé.  Il prenait à peu près 10 minutes pour scelléBearacuda, mais SubmURSA peut être sceller en à peu près 30 seconds à cause des nouveaux loquets.


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