Pacific Nautilus

Pacific Nautilus Autonomous Underwater Vehicle 2009 Journal Paper

DeltA (AKA Fat Man) NSBE-SDCC and MRO Members of Pacific Nautilus

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Pacific Nautilus Christopher-Lorenzo Carter, Steven Keeton, Colin Bradbury, Yama Khuu, Mark Halls, Kyle Kurch, Aaron Werner, Michael George in conjunction with: National Society of Black Engineers-SDCC Mesa Robotics Organization http://www.pacificnautilus.org

Abstract Since 2005 community college students from the San Diego Community College District have come together to in the spirit of hard work, experience and dedication. This work ethic makes up the majority of community college students who transfer to four year institutions to complete their degree. Our members and their organizations come together to solve real-world engineering problems by using real life experience, which they apply in addition to college education, to produce solutions. The majority of the students are from Electrical, Mechanical, Aerospace, Civil, Structural, Bio or Computer Engineering with some from Math and Business disciplines. Students from the first community college to enter this competition have regrouped under Pacific Nautilus and added member organizations in order to recreate this effort at additional community colleges and universities to share the knowledge, experience and training we have acquired. Pacific Nautilus is now in its fourth year as an organization and its third entry into the AUVSI and ONR’s Annual Autonomous Underwater Vehicle Competition. Pacific Nautilus’ DeltA Fat Man is designed to operate autonomously in depths of up to 2

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atmospheres. Within the custom hull of the vehicle, a series of microchip microcontrollers analyze data from cameras, hydrophones, gyroscope and absolute pressure sensor and as well as output to custom motor controllers to propel the vehicle through the obstacle course.

1. Introduction The Autonomous Unmanned Vehicle Systems International (AUVSI) and the Office of Naval Research (ONR) are sponsoring the twelfth annual international autonomous underwater vehicle competition to be held in San Diego, California at the SPAWAR facility July 28th through August 2nd. A student team, under Pacific Nautilus, made up of the National Society of Black Engineers – SDCC (NSBE-SDCC) and the Mesa Robotics Organization (MRO) will be developing a new Autonomous Underwater Vehicle (AUV) to enter this year’s competition. NSBE-SDCC and MRO have engaged in research that strays away from its contemporaries and has engaged in a cutting edge multiuse platform. The control system developed will be able to control ground and surface water vehicle in future implementations of these vehicles.

2. Mechanical Platform Hull Design Utilizing Pro/Engineer Wildfire 4.0, precision parts are designed and manufactured in a 3D environment to reduce prototyping time and virtually eliminate human error. Originally modeling of the models was done by creating a single solid part, but this was later determined to be extremely inefficient due to the guesswork involved when fabricating the vehicle. It was later established that modeling each individual part of the vehicle and then

3D View

assembling them within the Pro/Engineer environment was the most efficient process. Beginning with a basic box shaped design, named the Model A, in order to take full advantage of laminar flow, the prototype proved effective in maintaining a steady course by traveling within a single plane of water. This proved essential in the development of the next stage of the design, referred to as the Model A Delta (Delta). By studying the designs of current Avionics platforms such as the Concord and the F-22 Raptor and adopting the delta wing model, the latest prototype achieved reduced resistance while maintaining its stability. Throughout the prototyping process it was

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discovered that the reduced internal volume was insufficient for the range of components required. By merging the previous designs, full advantage is taken of both the stability of the original Model A and the reduced drag of the Model A Delta.

Thrusters Three Seabotix SBT 150 thrusters power the DeltA, which are mounted directly to the hull. Two are mounted horizontally to provide forward thrust, while the third is mounted vertically in the front to provide vertical thrust. Each thruster provides 4.85 lbs-ft at 4.25 amps and 19 VDC, with a peak thrust of 6.4 lb-ft by increasing current for short periods.

Seabotix SBT 150 Thruster

Our Seabotix thrusters come with Subcon four pin male connectors which we matted with a four pin female wet mattable connector.

Wet/Dry Connectors

The outer box uses three water-proof cable glands with through hole bushings in each, one three hole bushing for thruster control, and the other two are 4 hole bushings for the three hydrophones, 2 lights, 2 cameras and pressure transducer. The inner box has one Seacon AllWet connect with 24 pin outs in a pie shaped configuration with six connecters having 4 pin out each

Appendix page for Power distribution Chart.)

The fourth battery is utilized to power the controller boards.

3. Electronic Hardware Batteries The AUV is powered by four 11.1 V Lithium Ion 4400 mAH batteries that provide 48.8 Wh at 4A with a maximum of 12.6 V peak and a cutoff Voltage of 7.5 V. Three 11.1 V batteries are used in parallel to offer 11.1 Volts at 13.2 Amps to power the three Seabotix SBT 150 Thrusters. (See Figure 1 in

Each battery has a PCB installed with the battery pack and protects the battery from: • Overcharge (>12.6V) • Over discharge( <7.5 V) • Over drain ( >10 Amp) • Short circuits • Max discharging rate of 4A The four batteries are enclosed in a waterproof/fire retardant ABS enclosure with silicon sealing wire. The Seabotix thrusters, when running at 19 Volts and max current of 4 amps, use about 80 watts of power. The thrusters will be running at 11.1 Volts. The thrusters draw 3.75 Amps of current therefore we will use 41.6 watts of power. The H-bridge will be supplied with 11.1 Volts and 13.2 Amps, thus

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supplying the thrusters with about 146.5 Watts of power. The minimum voltage before cut off is 7.5 Volts therefore we can run the vehicle for about 3 hours if we completely drain the batteries to their cutoff voltage. The standard charging time is 4 hours per battery. We have two smart chargers in which to charge the batteries, and therefore need to plan for up to an 8 hours down time in which we would have no batteries for our vehicle. Since LiPo batteries have no memory affect we could theoretically charge them during any break in test runs and between qualifying runs towards the end of the week.

Motor Control/H-Bridge The H-bridge circuit board contains three Hbridge circuits derived from the Open Source Motor Controller (OSMC). It accepts the differential PWM outputs from the motion controller board and generates the appropriate power for the three Seabotix SBT 150 thrusters. Each H-bridge circuit can deliver up to 10 amps at 24 volts, whereas the current vehicle only requires up to 4 amps at 12 volts. The use of differential PWM signals eliminates the need for a common ground link between the circuit boards, thereby allowing each circuit board to run on its own independent power subsystem.

Microcontroller The custom motion controller circuit board takes in analog data from a pressure transducer, a two-axis tilt sensor, and a yawrate sensor. Based on this information, it generates PWM output signals to control up to four bidirectional motors. The selected microcontroller to perform this task is the Microchip PIC18F2525. The operations are controlled by commands received over a UART serial interface. The circuit board also has an SPI interface for controlling additional thrusters.

Members of Pacific Nautilus

Hydrophone array controller The custom acoustics board takes in analog data from three hydrophones and determines the relative direction to the pinger. The selected microcontrollers for this task are three dpPIC33FJ12 digital signals processors (DSPs) and a central general-purpose PIC18F26K20 microcontroller. Each DSP takes the input signal from one hydrophone, performs a 4-pole Chebyshev band-pass filter and then examines the result for the presence of an acoustic signal of the designated

Custom Controller Board

NSBE-SDCC and MRO

Custom H-Bridge Board

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frequency; the timing parameters of the acoustic signal are then communicated to the central microcontroller via an I2C interface. The central microcontroller generates a common sampling trigger signal so that the DSPs are all synchronous with each other. The central microcontroller is responsible for the mathematics for determining the pinger direction; this information is then passed upward to the mission-control algorithms which are currently co-located in the central microcontroller.

Hydrophones We are using custom built hydrophones provided by LAB-Core Systems. The hydrophones are mounted to wings below the hull arranged in an equilateral triangle. The hydrophone outputs are fed into a custom built circuit board housing three dpPIC33FJ12 digital signals processors (DSPs) and. The signals are then sampled through a central general-purpose PIC18F26K20 microcontroller.

LAB-Core Systems Custom Hydrophone

In the course of developing the Pacific Nautilus AUV’s we have published a number of white papers to document the development of the hydrophone system. The Hydrophones Mathematical Model, Hydrophone Sampling and Pyramid Search paper was developed in cooperation with Pacific Nautilus by Dr. Colin Bradbury who is a respected member of our team and a trusted adviser.

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Additionally, Dr. Bradbury developed a program to mathematically simulate the signal detection and bearing calculation task. The Hydrophones Model Program was used to determine the most efficient configuration for the hydrophone array and to investigate various bearing analysis algorithms.

4. Software and controls The control system uses a Pic18F2525 Microcontroller to read data from the analog absolute pressure sensor in order to obtain our depth, a dual axis accelerometer to determine our tilt angle, a gyroscope to determine our yaw rate and to generate 3 PWM signals to control our left, right and center thrusters. We are using C to program our control micro controller using Microchip’s MPlabs IDE. Our motion control software is broken down into 7 files. These file separate common algorithms to simplify debugging, controller changes, sensor changes and code modification.

5. Vehicle Testing Hull Prototyping After a group consensus to use acrylic for our hull design we made a steady effort to begin experimenting with scrap pieces. Our first project was to simply bond two ¼ inch acrylic sheets together edge to face with #16 clear, medium bodied solvent cement acrylic welding material. After becoming comfortable with the welding process we set a goal to create a water proof ½ scale prototype of the original model A. We were not too successful in our first fabrication and found it difficult to properly seal our longer pieces. After a bit of researching and professional consultation we found the welding process was made more easy and effective when the edges were precisely cut and polished. Taking a step back we fabricated a small box with a removable sealable lid for proof of concept. To finish and ensure an even bond we used a diluted welding solvent #3 with a hypodermic needle to fill voids in the original weld. We were beginning to find success in our welding capabilities yet were now finding leaks around our fastener sites. We moved to use ½ inch aluminum hardware to mount our lid with extra gaskets around the bolt heads and between the thread site and lid surface. This proved effective and we are now fully confident in our water tight system. We then built a second prototype of the original "model A" and another of the delta wing design. These two prototypes led us to "DeltA," "A.K.A. Fat Man" and now have two hulls in production.

Waterproofing

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Our method for waterproofing is a simple gasket and flange plate design that allows us to access our power site, controller boards, and other parts. All of our exterior component wiring will be fed bulkhead connectors with rubber bushings and finally spliced into a waterproof bulkhead connector that is fitted to our interior power and controller box.

6. Conclusion The entry of the Fat Man is the culmination of four years of thought and effort from team members past and present. This idea in one form or another has been discussed and planned by some very bright and talented students since our inception. We are very proud of our first custom fabricated hull, motor controller board, H-bridge and hydrophone DSP. Community college students bring life experience as well as curious minds which makes our entry into this competition very interesting.

7. Acknowledgments Corporate Sponsors We would like to thank our corporate sponsors who have not only empowered us reach new heights, but filled us with greater confidence that we are headed in the right direction with our research and that the advances we are making in some of our technology can lead to greater understanding and impact in the field of autonomous vehicles. Both Jerry Gruen & Darci Bushy from Lockheed Martin have been a great source of support and encouragement. Don Rodecker from Seabotix, who we consider a friend and mentor in the field of AUV/ROV’s, has supported us from the

beginning of our project. Brock Rosenthal from Ocean Innovations and Ronald Perez San Diego Seal are new sponsors for Pacific Nautilus and we look forward to collaboration with them in the future. Seacon and Microchip have supplied us with needed resources to complete our project. Advisers and mentors The following advisors have not only been an inspiration, but have made our learning and research fun and rich in depth and breath. Thanks: Dr. Colin Bradbury, Dr. Michael George, Professor Duane Wesly, Professor Morteza Mohssenzadeh with out whom we would not made such significant progress. Through SIFE (Students in Free Enterprise) Dr. Leroy Brady has handled our accounting and accountability to our sponsors. This will allow us to account to our sponsors our expenditures fully. Thanks to San Diego Mesa College who has supported this project with open arms.

Side View

This is the outer hull through which we slide the inner control box. This acrylic hull design gives the vehicle stability and has increase laminar flow which eliminates two degrees of freedom allows for simpler single plane control.

Inner Box

8. Appendix DeltA (aka Fat Man) Top View

The inner box is the crux of our new design. This inner box contains the batteries, motion control system, temperature sensor, dual axis accelerometer, link to our absolute pressure transducer, custom acoustics board and some room for additional sensors as needed. We will be able to move this control box to our surface water or ground vehicle, reprogram the micro controllers and control multiplatform vehicles with a single control system.

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This single source multiplatform approach will replace the current methodology currently employed by our military and civilian agencies that use remote operated or autonomous vehicles.

Outer hull

Exploded View

Removable Control box

This exploded view shows the complexity and sophistication of our first custom designed hull. This concept has great potential and takes advantage of low cost custom fabrication to offer a high performance cost effective platform that meets customer needs.

This box will be used in other autonomous vehicles allowing us to have a single control system for multiple platforms.

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Power Distribution Diagram

Figure 1. This power distribution system incorporates the elements that are currently implemented with the additional potential to be expanded for future growth.

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