ARVP’s previous autonomous underwater robot, AquaUrsa, was retired after 4 years and three major rebuilds. Even though AquaUrsa had shown fantastic reliability within the last few years, signs of fatigue and material failure led the mechanical team to the retirement decision in 2016. A subteam was created early that year dedicated to designing a new robot for Robosub 2017. In December the robot’s design was finalized, the engineering calculations were completed and the robot was named Auri.
Inspired by the fictional spaceships TIE Fighters from the movie franchise Star Wars, an octagonal outline was given to Auri. In Auri’s design process, the team aimed for keeping AquaUrsa’s best characteristics and improving the weaknesses. The aluminum frame and the transparent acrylic hull were two of the most important characteristics that were passed on to Auri. Three subassemblies were also successfully integrated into Auri without any changes from when they were used on AquaUrsa (battery enclosures, torpedo assembly and the marker droppers). With 6 degrees of freedom in compared to 5 in AquaUrsa, a 30-pound drop in weight to 60 pounds and a significantly cheaper cost of manufacturing, Auri is without doubt the most incredible underwater robot that ARVP has ever designed.
The hull for the new robot was completely redesigned. The best parts of the old design were kept in mind, but new innovative ideas were also incorporated to solve issues from previous years. The final design is strong, convenient, practical, and aesthetically pleasing. It is composed of a central aluminum section from which the electronics trays are supported and two acrylic tubes on either side which cover and house the trays. The elegant, clear ¼” acrylic tubes allow for both amazing visibility of the electronics trays and easy access as the tubes can quickly be removed to expose the trays. This means that the trays, although easily removed themselves, can be worked on without detaching them from the robot. The inner diameter of the tubes is 7.5”, which is much smaller than that of the previous hull. This was chosen to reduce the buoyancy of the robot and thus reduce the weight required to sink it. The end caps are also disks of clear acrylic to provide clear visibility for the onboard cameras. The cylindrical shape of the acrylic allows for even pressure distribution to reduce stress and the octagonal shape of the aluminum section provides multiple flat surfaces for easy mounting of components.
Aluminum was chosen for the central section because of its non-magnetic property so it would not cause a magnetic interference with any of the electrical components. It is also very easily machined, allowing for this custom octagonal shape to be made. The flat surfaces of the central section allow for subconn connectors and cable penetrators to be mounted for connection between the electrical boards inside the hull and the components outside of it. The cylindrical steps on either side of the aluminium allows for two sets of o-rings to be mounted to provide a watertight seal on the hull. There is also versatility in the orientation of the electrical trays as they can slide into the hull in either the horizontal orientation or the vertical orientation depending on current preference.
Auri’s frame was designed to be more compact, functional, and aesthetically pleasing than ARVP’s previous robot. The hull is friction-fit with two complete octagonal rings that are bolted to two L-bars. Attached to these bars are six aluminum ribs, making up the two wings. All components are located inside the wings, providing protection during transportation. Moreover, portability is increased due to four rubber handles attached to the ribs. Bolted to the ribs are multiple trays and side panels. The trays and panels allow for the easy attachment and removal of a variety of components, including torpedoes, thrusters, and marker droppers. The new frame design embodies compactness without sacrificing functional space; this allows for mounting of future mechanisms such as a cooling system or mechanical arm.
Auri has two separate battery enclosures, which rest by the hull on aluminum sheets that are mounted to the frame.The battery enclosure is made out of 3.5-inch acrylic cylinders, which is sealed at both ends with aluminum o-ring flanges. The caps of the assembly are designed with 1/2-inch acrylic ends.
Marker Release Mechanism
Auri has been equipped with two marker droppers located underneath the pressure hull. The markers themselves are torpedo shaped steel tubes fitted with acrylic fins to ensure stability and optimum accuracy. The marker release mechanism used involves holding the steel markers in place by a magnet. When the target area is identified by the interior cameras, a waterproof servo will move the magnetic field away from the dropper causing it to fall onto the target area. The component housing was 3D printed out of ABS plastic to ensure that the magnetic nature of the system is not compromised by other ferromagnetic metals. This also makes for a simpler machining process.
The torpedo launching module was designed to occupy the least amount of space while delivering the required pressure to propel the torpedoes. This was accomplished using CO2 cartridges that are small as compared to an air tank. The torpedo launching module consists of a CO2 bucket changer that allows for the quick replacement of the cartridges. The bucket changer is directly mounted onto an on/off ASA regulator. This on/off regulator is connected through a 90-degree fitting to a variable pressure regulator that decreases the CO2 pressure from the cartridge to the desired value. The pressure regulator is threaded into an aluminum connection piece with a female end. A ¼” fitting is used to directly mount the aluminum piece to the 2-way solenoid valve. This design is rigidly mounted to Auri with the mounting plate from the solenoid valve and eliminates the use of macroline. Mounted on both solenoid valves is a solenoid-to-tube connector that is press fitted with a 123mm stainless steel pipe. The torpedoes are held on these pipes with the aid of o-rings. After the entire system is pressurized with CO2, an electrical signal is sent to the appropriate solenoid valve. This signal opens the valve allowing for CO2 to escape from the launch pipe to propel the torpedo forward. The torpedoes were 3D printed using PLA as the filament.