cornell university autonomous underwater vehicle: design ...€¦ · abstract—thor & loki are...

Cornell University Autonomous UnderwaterVehicle: Design and Implementation of the

Thor & Loki AUVsNicholas Akrawi, Mustafa Ansari, John Bartlett, Zander Bolgar, Timothy Braren, Jonathan Chan, Richard Chen,Eric Chiang, Julia Currie, Nancy Ding, Joseph Featherston, Jennifer Fuhrer, Christopher Goes (lead), Shantanu

Gore, Andrew Halpern, Brendon Jackson, Sanika Kulkarni, Joshua Lederman, Alan Lee, Laura Lee, Noah Levy,John Macdonald, Artina Maloki, Mihir Marathe, Kristina Nemeth, Alexander Ozer, Kai Pacheco, Cora Peterson,

Danny Qiu, Alexander Renda, Nicholas Sarkis, Daryl Sew, Alexander Spitzer, Emily Sun, Chesley Tan, EllenThiel, Ian Thompson, Samuel Tome, Patrick Wang, Nancy Wang, James Wu, Angela Yang, Evan Zhao

Abstract—Thor & Loki are the new 2015-2016CUAUV autonomous underwater vehicles (AUVs),designed by a team of 45 undergraduate students atCornell University. Completed in a ten month designcycle, both vehicles were fully modeled using CADsoftware, extensively simulated with ANSYS, andmanufactured almost entirely in-house. The designsof Thor and Loki draw heavily upon over 15 years ofaggregate research and development to enhance au-tonomous underwater vehicle technology by CUAUVmembers.

Notable new advancements include quick-maintenance sliding racks, four dynamically vectoredthrusters, a revamped serial protocol supportingonline code flashing, and a full software simulationsystem complete with an integrated physicsengine, three-dimensional vehicle and environmentvisualization, and automated mission testing andverification. Thor and Loki’s combined sensor suitetotals four inertial measurement units (IMUs), fiveCMOS cameras (three forward, two downward),a Teledyne RDI Explorer Doppler Velocity Log,two depth sensors, two internal pressure sensors,one full and one partial hydrophones arrays,and a BlueView high-definition imaging sonar.Returning features include vacuum-assisted sealing,hot-swappable batteries, six degree-of-freedomcontrol, and pneumatic actuator systems on bothsubmarines.

I. INTRODUCTION

THE Cornell University Autonomous Un-derwater Vehicle team’s primary objective

is to design and build an autonomous underwa-ter vehicle (AUV). The AUV is a cumulative

product of many integral end-to-end projectsthat necessitate extensive hands-on experience,critical problem-solving skills, and interdisci-plinary collaboration amongst students. Uponcompleting the vehicle in a ten month designcycle, CUAUV participates in the annual AU-VSI Foundation and ONR International Robo-Sub Competition. The competition is held inlate July at the TRANSDEC facility, part ofSPAWAR Systems Center Pacific in San Diego,California.

RoboSub is designed to challenge student-built AUVs with an obstacle course that simu-lates real-world AUV missions such as accurateseafloor mapping, subsea infrastructure con-struction, and precise underwater object manip-ulation. RoboSub competition tasks range fromshape and color recognition to torpedo firingand fine control of small objects. Each of thesetasks must be completed by the vehicle au-tonomously (without any human interaction orcontrol). Successfully completing such tasks re-quires accurate visual and acoustic detection ofcompetition elements, fine-control navigation,obstacle avoidance, and object manipulation. Inorder to complete the task of building a vehiclethat is capable of navigating all mission ele-ments and meeting all requirements, CUAUVis divided into four subteams: mechanical, elec-trical, software and business/public-relations,each of which is divided further into project-specific working groups.

Cornell University Autonomous Underwater Vehicle 1

II. DESIGN OVERVIEW

The 2015-2016 primary vehicle, Thor, andthe 2015-2016 secondary vehicle, Loki, areboth hovering, littoral-class AUVs designedprimarily to compete in the RoboSub competi-tion. Their designs, built on those of previousyears, are similar to that of work or observa-tion class remotely operated vehicles (ROVs),primarily targeting space-constrained complexfunctionality and fine-grained positional con-trol.

Thor and Loki are designed to work in tan-dem to complete the RoboSub course faster andmore reliably than would be possible with onlya single submarine. An underwater acousticcommunication system allows the submarinesto transmit task status and submarine state backand forth in realtime as the mission progresses.This communications link can be used to al-low the two submarines to share course stateinformation (more accurate element positionsbased on new observations) and take over fromone another should unexpected problems occurduring mission execution.

III. THOR

Fig. 1: A SolidWorks rendering of CUAUV’s2016 primary vehicle, Thor

Thor is an improvement over CUAUV’s pre-vious vehicles in terms of fine control, ro-bustness, and ease of assembly. Robustnesswas improved through more extensive electricaltesting, a stiffer frame base, and a simulatorto test mission code before the AUV wasmanufactured. Added space was strategically

positioned for ease of assembly and testing ofenclosures. Removable SEACON panels wereadded to decrease time and increase ease ofelectrical assembly and integration. Eight BlueRobotics brushless thrusters give Thor controlover six degrees of freedom. The location ofsurge thrusters on extended arms improves sta-bility in movement. The vehicle also includesa pneumatic actuator system that allows it tointeract with its environment. Thor measures43 inches in length, 35 inches in width, and 15inches in height. Its dry weight is 81 pounds.

Custom electronic boards designed by stu-dents are isolated in the aft hull and work asinterchangeable boards connecting to a centralPCB backplane via PCI-express style card edgeconnectors. The vehicle is powered by twolithium-polymer batteries and contains modularpower, sensor, and serial communication sys-tems. A full onboard suite of visual, acous-tic, inertial, and pressure sensors is used fornavigation and data collection. The vehicle’ssoftware suite is run by an integrated computerwith a quad-core hyperthreaded Intel i7 CPU,and is primarily composed of intercommunicat-ing shared memory, serial, control, vision, andmission systems.

A. Mechanical Systems

Thor’s mechanical system consists of thevehicle frame, upper hull, actuators, and ex-ternal enclosures. The upper hull and exter-nal enclosures are responsible for protectingthe electronic components from water, whilethe structure provides mounting points andprotection for sensors, enclosures, and actua-tors. Assemblies are designed in SolidWorks,simulated using ANSYS finite element anal-ysis (FEA) software, and then manufacturedeither manually or with the help of CNCmachinery and computer-aided manufacturing(CAM) software (Pro/TOOLMAKER and Fea-tureCAM).

1) Frame: The frame defines the positionsand orientations of each mechanical component


in the vehicle, maintaining the structural in-tegrity and rigidity of the vehicle and protectingdelicate components. Intensive FEA was doneon the frame to ensure that it would be ableto protect all the components within. Thor’sframe implements a modular method of compo-nent attachment. Water-jet cutting allowed forrapid manufacture of frame components and forspeedy assembly and testing.

Fig. 2: Thor’s frame.

Most of the components on the vehicle arescrewed directly to the frame, requiring noextra mounting features. This saves weight,reduces complexity, and allows for efficient useof space. All components are placed such thatthe center of mass is at the relative center ofthe AUV. The frame emphasizes ease of use,manufacturing, and integration whilst remain-ing adaptable.

2) Upper Hull and Electronics Rack: Thor’supper hull is composed of two racks joinedby a midcap, undersea connectors, the DVLtransducer head, and two acrylic hull assem-blies that protect the electronics. The fore rackcontains all commercial off-the-shelf (COTS)components in the upper hull including theCOM Express module, DVL electronics, andLCD display.

The aft rack contains all custom electron-ics linked together via an easily customizablebackplane system. All boards slide into con-nectors via 3D printed rails. Both racks aremounted on easy to use, custom rails whichallow the electronics to slide away from themidcap and the internal wiring to be reachedand modified easily.

Fig. 3: Thor’s fore and aft racks and midcap

All connections to the outside of the upperhull are made via SEACON connectors locatedon the midcap panels. These panels screw onto the midcap and allow parallel integrationand maintenance of the SEACON. The midcapprovides mounting for both the fore and aftracks, the DVL transducer head, and the sen-sor boom. Although difficult to manufacture,the midcap makes efficient use of space andmaterial, while minimizing the risk of leaks.The two acrylic hulls slide over the cantileveredracks to provide sealing. Redundant sealing ofthe hulls as well as a slight vacuum within theupper hulls renders hull leak risk negligible.

3) Actuators: The actuators system is com-prised of two torpedo launchers, two markerdroppers, one active downward manipulator,and one passive forward manipulator. A 3000psi paintball air tank regulated down to 100psi serves as the air supply for the pneumaticportion of the system. Fourteen valves housedinside a custom enclosure regulate the flowof the compressed air to the rest of the ac-tuator system. With this configuration, Thorcan independently fire individual torpedoes andmarkers, and actively grab and release objects.

4) Torpedo Launcher and Marker Drop-per: The torpedoes and markers are customdesigned and cast projectiles made to travelaccurately through the water. Torpedoes arepropelled pneumatically and have a range ofapproximately 15 feet. Markers are held inplace by magnets until a small air burst unseatsthem, after which their path downwards is heldstraight by large fins and heavy tips.

5) Active Grabbers: The grabber is respon-sible for grabbing the recovery objects. It


Fig. 4: Thor’s solenoid valve enclosure

consists of a custom pneumatic linear pistonconnected to a scissor arm. On the end of thescissor arm is an array of electromagnets thatcan be turned on and off to magnetically grabthe doubloons. The grabber is also capable ofmounting a second custom piston. The pistonis double-action: firing one valve closes thescissor arm and firing the other opens it.

Fig. 5: Thor’s downward grabbers

6) Forward Manipulator: Thor features apassive forward manipulator utilized to removecovers on mission elements. Two X-shapedcontact elements serve to automatically guidethe handle of the lid into the sub’s grasp. Thecontact elements contain a spring and Halleffect sensor system that serves as a touch

sensor on the forward manipulator.

Fig. 6: One of Thor’s forward manipulators

7) Thrusters: Propulsion is provided byeight Blue Robotics T200 brushless thrusters.Four thrusters are mounted on stepper-controlled mounts, enabling dynamically di-rected thrust vectoring for improved handlingand speed. This vector thrust system provides360 degree rotation of the four depth/surgethrusters. An CNC-machined enclosure housesa NEMA-23 stepper motor, a custom electronicdriver PCB, a custom encoder to determine thedirection of the thruster, a worm gear system,an encoder magnet, and an output shaft. Thor’sthruster mounting scheme provides the vehiclewith active control in all six degrees of free-dom.

Fig. 7: One of Thor’s vectored thrusters

8) External Enclosures: Thor’s external en-closures contain various electrical systems lo-cated outside of the upper hull pressure vessel.These waterproof vessels isolate the systemsfrom unwanted noise and allow for flexibilityin the construction of the vehicle. Systemscontained in external enclosures include thehydrophone acoustic system, kill switch, sensorboom, downward camera, and battery pods.

9) Hydrophones Enclosure: The hydro-phones system is kept separate due to noise


considerations. The enclosure was designedto be as light as possible and is constructedentirely out of aluminum to facilitate effectivecooling. In addition, the piezoelectric elementsof the hydrophones system are mounted di-rectly to the wall of the enclosure, eliminatingthe need for a separate mount for the elementsand keeping the system compact.

10) Sensor Boom: Some of the vehicle’ssensors must be isolated from the electromag-netic noise caused by thrusters and other high-power electrical components. The sensor boomis mounted atop the midcap far from any othernoise sources in order to maintain signal in-tegrity. It contains a LORD MicroStrain 3DM-GX4-25 AHRS and a SparkFun MPU-9150.

11) Battery Pods: Two lithium-polymer bat-teries allow for hot-swap battery changes with-out powering down the AUV. Each batterypod features two SEACON connectors, onefor monitoring temperature, and the otherfor charging and discharging the batteries. ADeepSea pressure relief valve also prevents anybuildup of internal pressure, removing the dan-ger of explosion due to out-gassing. The batterypod lids are latched to the hull with latches forquick battery removal and replacement.

Fig. 8: Thor’s battery pod enclosure

B. Electrical SystemsThe electrical subteam designed and pop-

ulated custom circuit boards with the assis-tance of various schematic and PCB softwarepackages. The dual-hull design of the vehicleemphasizes the strategic placement of electron-ics and wire management by dividing COTS

devices from custom electronic boards. As aresult of this and improved PCB back-planeusage, electrical connections are optimized be-tween boards inside the hull, external enclo-sures, and sensors exterior to the upper hull.

Fig. 9: The redesigned aft-rack back-plane

1) Power System: Thor’s electrical systemssupply up to two hours of reliable powerthroughout the vehicle and provide an interfacebetween the on-board computer and all sen-sors and peripheral devices. The power to runThor is provided by two Advance Energy 8000mAh lithium-polymer batteries. To facilitateuse of the vehicle on shore, a bench powerstation has been developed to power the subfrom a standard AC power source. The inputpower sourced from the two batteries is routedthrough the merge board, which combines thetwo power sources to provide a single powerrail for the vehicle. To ensure nominal andequal discharge from both battery packs, themerge board constantly compares the voltagesand drains power from the battery with higherpotential.

In order to ensure reliably regulated power,the power distribution board provides the elec-trical system with isolated power rails at +5,+12, +24, and +48 volts. The board measurespower use from each channel and passes thesestatistics to the computer. In the case of exces-sive current draw, the computer has the abilityto shut down the corresponding port to preventpotential damage to the components.

2) Serial Communication: The serial boardis the interface between the computer and thevarious sensors and custom-designed boards.


It allows sixteen devices to communicate viaRS-232 serial through two USB connections tothe computer. The RS-232 protocol was chosenbecause of noise tolerance and ease of use anddeployment.

Fig. 10: The serial board implementation fea-turing the back-plane edge connectors

3) CAN Bus: The CAN protocol is usedto communicate with each of the four vectorthrust modules. CAN was chosen over RS-232 because all the connected devices shareonly two communication wires. This allowsthe connection to all the vector thrust modulesto be identical and allows connections to beswapped without effect. Each board is issueda unique device ID to enable individual vectorthrust control.

4) Thruster Control: Each of the eightthrusters is controlled by a custom brushlessmodule, contained within the main hull. Eachboard contains a microcontroller to communi-cate with a primary thruster board. To abide bysafety regulations, all thruster modules, vectorthrust modules and the actuator board can behalted either by hardware switch or software.

5) Vectorized Thruster Control: Each vectorthrust module contains a stepper motor anda custom controller board. This board con-tains two H-bridges to drive a bi-polar steppermotor and communicates with the computerover the CAN bus. The board shares a con-nection interface with the other vector thrustermodules, simplifying connections and allowingthe devices to be swapped without softwareremapping.

6) Actuator Control: The actuator boardcontrols the solenoids necessary for all of the

pneumatic manipulators on the sub. The ac-tuator board accepts commands to control thesolenoids and an additional two DC motors orone stepper motor through communication withthe computer using an isolated serial line.

7) Sensor Interface: The General PurposeInput Output (GPIO) board has multiple portsto read and write analog and digital inputs toand from sensors. It is primarily designed toprovide the electrical system with extra modu-larity, as there is often a need to add sensorsor electrical devices later in the design process.In addition to reading measurements from thedepth sensor, GPIO monitors internal pressureof the vehicle to ensure that partial vacuumis maintained. GPIO also contains a customdesigned Power Over Ethernet (POE) injectorfor powering our two forward cameras.

C. Sensors

In order to autonomously navigate throughthe competition course, Thor is equipped withtwo main classes of sensors: sensors to observethe vehicle’s external environment, and sensorsto determine the vehicle’s state. Visual recog-nition and navigation tasks in TRANSDECare successfully identified using two forwardcameras and one downward camera, and high-definition imaging sonar, while the pinger-localized tasks are handled by the hydrophonessystem using a passive acoustic array. Thestate of the vehicle is measured using inertialmeasurement units (IMUs), compasses, a depthsensor, a Doppler Velocity Log (DVL).

1) Hydrophone Array: Thor’s hydrophonesystem uses three Reson TC-4013 piezoelectricelements to detect incoming acoustic waves.The design was optimized for functionalityand affordability utilizing a microcontroller andcustom analog filtering to interpret the elementdata. The hydrophone system accurately cal-culates the heading and elevation of a pingerrelative to the vehicle within one degree. Thehydrophone system has also been extended tostream data over Ethernet to the vehicle’s maincomputer which hosts a platform for real time


acoustic debugging and finer tuning of theoverall system.

In tandem to pinger tracking, the hydrophonesystem enables acoustic based communicationand data transfer between Thor and Loki. Oneof the piezoelectric elements serves to bothtransmit and receive acoustic signals. Reliablecommunication is vital for multi-vehicle per-formance. Transmission data includes vehicleand element positions, mission task completionstatus, and vehicle state information.

Fig. 11: The hydrophone system board imple-mentation, featured in both Thor and Loki

The hydrophones system consists of threemain components: the Ethernet-based commu-nication to the computer, the transmit (ampli-fier) channel, and the three receive based chan-nels. The transmit channel is created by usingan onboard digital-analog converter (DAC) tocreate an output frequency, a 40V rail-to-railamplifier, and an output transducer connection.The board communicates with the sub com-puter via an Ethernet port (using an ethernetphy and IP stack), and transmits raw timedomain data to the computer for processing.The computer is used to control the receivegain settings, output frequencies, and severalmiscellaneous board settings. Data transfer isfacilitated via a simple frequency-shift keyingcommunication scheme, and is implementedonboard, which can be fine tuned via software’sshared memory system. An improvement uponthe previous version of this system was to runan IIR filter for each frequency we care tolook at (in the 25 - 40 kHz range) insteadof running continuous FFTs, thus decreasingcomputational complexity by about O(n). Thus,

we have managed to simplify the identificationof frequency and phase tracking to determinethe direction of the pinger.

2) Orientation: A combination of IMUs andcompasses measure the vehicle’s acceleration,velocity, angular velocity, and spatial orienta-tion. The orientation sensors on the vehicleare a MicroStrain 3DM-GX4-25 AHRS anda SparkFun MPU-9150. An MSI Ultra-stable300 pressure sensor measures the depth of thevehicle.

3) Doppler Velocity Log: The Teledyne RDIExplorer Doppler Velocity Log (DVL) providesaccurate three-dimensional velocity data. Thisinformation is used in conjunction with theother sensors to provide closed-loop vehiclecontrol.

D. SoftwareAll of Thor’s higher level functionality, in-

cluding autonomous completion of missiontasks, is achieved through the vehicle’s soft-ware system. The software stack is built uponthe Debian GNU/Linux operating system andincludes a custom shared memory state syn-chronization system, a serial daemon for com-munication with the majority of the electri-cal boards, multithreaded vision, model-basedcontrol, localization, simulation, and abstracttask/mission systems. Our custom software isprimarily written in C++ and Python, withcertain subsystems in Scheme and Haskell.

1) Computer: Thor’s software is run on anIntel Core i7-4700 Haswell quad core processorhosted by a Connect Tech COM Express type 6carrier board along with an ADLINK Express-HL module, using a 256GB mSATA solidstate drive (SSD). The computer is connecteddockside through a custom Gigabit Ethernettether. A USB chip 802.11 adapter attachedto the computer provides short-range wirelessconnection capabilities.

2) Shared Memory: The shared memorysystem (SHM) provides a centralized interfacefor communicating the state of the vehicle be-tween all running processes, electronic subsys-tems, and users controlling the vehicle. SHM


is a custom system built upon POSIX sharedmemory, providing thread- and process-safevariable updates and notifications. Various ele-ments of the vehicle state are stored in and readfrom shared memory. These shared variablescan be accessed by all of the components ofthe software system concurrently, which allowsfor simple communication among the variousdaemons. Bindings to SHM, most of whichinterface with the C bindings through foreignfunction interfaces, are available for Python,Scheme, Haskell, OCaml, and Go.

3) Serial Daemon: The serial daemon isresponsible for syncing variables between themain computer and the electrical boards whichcontrol thrusters, actuators, sensors, and otherdevices. The serial daemon allows the com-puter to query the subs environment and controlthe subs behavior. Programs running on thecomputer, such as the controller and variousmissions, write values to variables in SHMwhich are then written to devices by seriald.Likewise, when devices modify their internalvariables, seriald reads their values and writesthem to corresponding values in SHM, allow-ing programs on the main computer to accessthem. The serial daemon enables any number ofdevices to read from and write to any numberof SHM variables across any number of SHMgroups.

4) Unscented Kalman Filter: Both sub-marines feature an Unscented Kalman filterwhich processes orientation data, in conjunc-tion with a standard Kalman filter for position.By using the unscented Kalman transform, theorientation filter is able to heavily reduce thecomplexity of processing nonlinear systems,while still generating accurately filtered output.The use of the unscented filter allows us touse highly nonlinear quaternions to representorientation, which do not suffer from the samelimitations as traditional Euler angles (i.e. gim-bal locking). This allows for a much morerobust controller and overall enhanced stabilityfor the vehicle.

5) Positional Controller: Positional controls(closing on absolute north and east positions)are achieved by a new navigational layer,which works by writing desires to the existingvelocity-based controller in a way that simu-lates positional control. In order to implementpositional control on top of velocity, a simplePID loop is used, which transforms positionalerror into a desired velocity. This design alsomakes it easy to enable optimizations; by de-fault, the positional controller automaticallycontrols submarine heading, orienting the subin such a way as to produce the maximumpossible thrust towards the desired destination.

6) Vision: Our vision-processing system isdesigned to give the vehicle up-to-date andaccurate data about the surrounding missionelements. A daemon for each camera capturesand passes raw camera frame data through anundistortion filter when necessary. This cameradata is then passed into shared memory forconcurrent processing by each vision mod-ule. The camera daemons and vision mod-ules are entirely modular, so that we canrun any combination of modules on eitherlive data or replayed logs. Undistorted data isthen analyzed using a combination of adap-tive color thresholding, Canny edge detection,contour analysis, Hu moment characterization,and neural-network based classification. Thorpossesses two IDS-uEye-5250CP Gigabit eth-ernet forward cameras, operating in stereo, anda downward-facing IDS-uEye-6250CP Gigabitethernet camera for perception of mission ele-ments located below the submarine.

Interprocess communication within the vi-sion system has been significantly updatedsince last year. Instead of using sockets todispatch images, we now use a set of sharedmemory blocks protected by read-write locks,with condition variables to ensure that visionmodules get notified of new frames as quicklyas possible. This system allows us to reachnear the speed of threading with the modularityof having entirely separate vision modules andcapture sources. We also revamped our vision


GUI to be served through a webserver, insteadof X-forwarded from the sub. This let us offloada lot of the performance hit of the visionGUI to the clients, and allows for multiplesimultaneous clients to view diagnostic outputfrom vision modules.

Fig. 12: Vision display/tuning GUI

7) Vision Tuning: A vision tuning systemenables fast, real-time adjustments to the visionparameters. The vision tuning user interfaceshows the results of intermediate steps andmakes it easy to see the outcomes of changesas they are made, allowing us to rapidly iter-ate upon our vision analysis algorithms. Eachmission element has its own independent visionmodule. This allows for multiple modules to berun in parallel.

8) Vehicle Logging: The logging systemcaptures the full shared-memory of the vehi-cle during mission runs. Furthermore, a logplayback utility allows the software team tosimulate the vehicle with real mission data andperform additional debugging and developmentout of the water. This system helps isolate bugswhich only occur rarely. The software stackfeatures a set of scripts which automaticallyupload all vehicle logs to CUAUV’s networkedserver at the end of pooltests for later debug-ging.

9) Mission System: Missions, the highestlevel of control code, are implemented ina functionally-inspired Python interface thatsplits vehicle goals into discrete, reusable tasks.This framework allows for direct control of

code execution without sacrificing ease of rea-soning. Tasks are created in a simple functionalstyle and can be composed to create variousnew useful tasks. The simplest combinatorsused are “Sequential” and “Concurrent” whichrun tasks in a serial or parallel fashion respec-tively.

10) Mission Simulation: A fast and extensi-ble networked simulator, written in C++ withan integrated physics engine, is used to rapidlytest mission logic against specifications. Mis-sion tests, which verify successful task post-conditions (e.g. ramming a buoy) given speci-fied preconditions (sub position, buoy position,vision error, etc.) are scripted in Scheme andrun mission code directly. The core simulatorinterfaces with our existing shared memorysubsystem, so simulated missions can be runwithout modification.

11) Visualization: The visualization engineallows for easy viewing of simulations andsubmarine missions, and can be fed by sensorinput during live runs to observe submarineorientation and movement. Our automated mis-sion testing engine, Peacock, interfaces withour visualization software to provide instantfeedback. In addition, simulated images pro-vide an endless stream of testing data for ourvision algorithms.

12) ASLAM: In order to accurately navigatebetween various elements during a run, oursub constructs a dynamically generated map ofobjects within the pool, updating the estimatedpositions of each object and the submarineas the mission proceeds and the submarineobserves mission elements in various positions.ASLAM utilizes a version of Sebastian Thrun’spublished FastSLAM algorithm, adapted to thethree-dimensional positional space of the sub-marine.

13) Control: Using continuously collectedand filtered vehicle state data, Thor and Lokiboth have precise and accurate vehicle controlfor all six degrees of freedom: surge, sway,heave, yaw, pitch, and roll. The vehicles usean empirically tuned PID controller for eachdegree of freedom along with a passive force


Fig. 13: CUAUV’s visualizer running a missionsimulation (skybox taken from pool photo)

model and continuous optimization. The mo-ment of inertia tensor of the vehicle is esti-mated from CAD to allow for better movementpredictions. Using this system, Thor can com-pensate for any drag and buoyancy forces, evenat non-trivial pitch and roll angles. The controlsystem enables high-level mission code to setdesired values for the velocity, depth, heading,pitch, and roll.

E. Mission Feedback and DiagnosticsThor features an onboard computer-

controlled color LCD display to provide visualfeedback of the vehicle’s current status, whichenables continuous monitoring of missionprogress during untethered runs. This allowsfor quick and easy reporting of vehicleinformation without the need for a computer,and is especially useful for system diagnostics,internal pressure monitoring, vehicle trimming,and thruster testing.

IV. LOKI

A. Mechanical SystemsLoki’s mechanical system consists of the

vehicle frame, upper hull, actuators, and ex-ternal enclosures. The upper hull is a single

Fig. 14: A SolidWorks rendering of CUAUV’s2016 secondary vehicle, Loki

hull design and protects the electronic com-ponents from water, while the frame providesmounting points and protection for sensors,enclosures, and actuators. Assemblies for Lokiwere also designed in SolidWorks, simulatedusing ANSYS FEA software, and then man-ufactured either manually or with the helpof CNC machinery and computer-aided manu-facturing (CAM) software (Pro/TOOLMAKERand FeatureCAM). Manufacturing for Loki wasprimarily aimed towards manual machining forsimplicity. Loki measures 21 inches in length,18 inches in width, and 17 inches in height. Itsdry weight is 33 pounds.

1) Frame: The frame defines the positionsand orientations of each mechanical componentin the vehicle, maintaining the structural in-tegrity and rigidity of the vehicle and protectingdelicate components. Intensive FEA was doneon the frame to ensure that it would be able tosupport the weight of the system and protectthe internal sensors and enclosures.

Loki’s frame consists of modular aluminumL-channels with material strategically removedfor weight savings while maintaining struc-tural integrity. The channels are easily screwedtogether to create the overall structure withmounting locations.

2) Upper Hull and Electronics Rack: Loki’supper hull is composed of a single rack at-tached to a CNC-machined end cap, the un-dersea connectors, the lithium polymer battery,and an acrylic hull assembly that protects theelectronics.


Fig. 15: A Solidworks rendering of Loki’sframe

The rack consists of all the commercial com-ponents, including a single forward camera andan Intel NUC computer, as well as the customelectronics boards and the 12V lithium polymerbattery. The rack is comprised of aluminumtrusses and Delrin rails that connect two alu-minum bulkheads. The boards either slide intothe Delrin trusses or are mounted via screws.All the boards connect to the SEACON connec-tors on the fore cap. The battery is also housedwithin the racks and rests upon Delrin rails withVelcro strips to secure it in place. The aft caphas a hole with a removable aluminum plugto allow for quick battery swapping withoutremoving the entire hull.

Fig. 16: A SolidWorks rendering of Loki’sUHPV

The fore cap provides mounting for therack, the depth sensor, the forward camera,the downward camera, and the piezoelectricelement. It also provides both sealing andmounting to the forward and downward cameraenclosures which protect the cameras. In-houseCNC machining of the front end cap allows forminimizing weight while maximizing strength.

All connections to the outside of the upperhull are made via SEACON connectors locatedon the fore cap. An acrylic hull is epoxiedto an aluminum collar and a CNC-machinedaluminum aft cap. The collar uses a doublebore seal for redundant sealing of the mainelectronics. The redundant sealing of the hullsas well as a slight vacuum within the hullrenders hull leak risk negligible.

3) Actuators: Loki’s actuators system iscomprised of two torpedo launchers, twomarker droppers, a passive downward manip-ulator, and one passive forward manipulator. ACO2 cartridge regulated down to 100 psi servesas the CO2 supply for the pneumatic portion ofthe system. Four two-way valves housed insidea custom, CNC-machined aluminum enclosureregulate the flow of the CO2 to the rest of theactuators system. The lid of the enclosure actsas the manifold for the valves. The smaller CO2

cartridge and the minimum number of valvesallows for the actuators system on Loki to bemuch smaller than its counterpart on Thor.

Fig. 17: A SolidWorks rendering of Loki’ssolenoid valve enclosure

4) Downward Manipulator: Loki’s down-ward manipulator consists of a static aluminumarm whose position can be manually changedso that it does not interfere when Loki is out ofthe water. On the end of the arm is an attachedX-shaped contact element which helps hook onto objects underneath the sub in order to movethem.

5) Forward Manipulator: Loki features apassive forward manipulator, very similar to


Thor’s, which is utilized to remove covers onmission elements. Two X-shaped contact ele-ments serve to automatically guide the handleof the lid into the sub’s grasp. The contactelements contain a spring and Hall effect sensorsystem that serves as a touch sensor on theforward manipulator. The arm of the forwardmanipulator mounts directly to Lokis frame.

Fig. 18: A SolidWorks rendering of Loki’sforward manipulator

6) Thrusters: Propulsion is provided by sixBlue Robotics T100 brushless thrusters: twosurge, two depth, and two sway. Loki’s thrustermounting scheme provides the vehicle withactive control in all six degrees of freedom.

7) External Enclosures: Loki’s external en-closures contain various electrical systems lo-cated outside of the upper hull pressure vessel.These waterproof vessels isolate the systemsfrom unwanted noise and allow for flexibilityin the construction of the vehicle. Systemscontained in external enclosures include the killswitch and the sensor boom.

8) Sensor Boom: Similar to Thor, some ofLoki’s sensors must be isolated from the elec-tromagnetic noise caused by thrusters and otherhigh-powered electrical components. It con-tains a LORD MicroStrain 3DM-GX1 AHRSand a Sparkfun MPU-9150. Loki’s sensor boomis a manually manufactured enclosure as op-posed to Thor’s CNC-machined enclosure.

B. Electrical Systems

Loki’s electrical systems feature a miniatur-ized version of Thor’s electrical system, provid-ing reliable power throughout the vehicle and

interfacing between the on-board computer andall sensors and peripherals within Loki.

Fig. 19: Loki’s legacy electronics rack

Due to Loki’s simplicity, a board-to-board,direct wiring system is implemented. The de-sign is similar to designs from years prior toGemini (prior to 2013).

1) Power System: Loki is powered by oneAdvance Energy 12 volt 8000 mAh lithiumpolymer battery, which gives the vehicle ap-proximately two hours of run-time. In order tomaintain constant up-time while testing, Lokiutilizes hot-swappable batteries, allowing forquick battery changes that do not require a fullsystem reboot. To facilitate use of the vehicleon shore, a bench power station has beendeveloped to power the sub from a standard ACpower source. The input power from the twohot-swappable battery ports is routed throughthe power distribution board.

In order to ensure reliable regulated power,the power distribution board provides the elec-trical system with isolated power rails at +5 and+12 volts. The board measures power use fromeach port and provides these statistics to thecomputer. In the case of excessive current draw,the computer has the ability to shut down thecorresponding port to prevent potential damageto the components.

2) Serial Communication: The actuator-sensor-serial (actusensor) board interfaces be-tween the computer and the various sensors


and custom-designed boards. It allows up toeight devices to communicate via RS-232 se-rial through one USB connection to the maincomputer.

3) Thruster Control: Each of Loki’s sixthrusters is controlled by an brushless ESC,contained within the main hull. A primarythruster board interfaces between the computerand each of the ESCs. Each ESC utilizes apulse-width modulated (PWM) signal from thethruster board to determine the brushless mo-tor’s desired state.

4) Actuator Control: The actuator-sensor(actusensor) board controls the solenoid nec-essary for all of the pneumatic manipulatorson the sub. The actusensor board also acceptscommands to control the solenoids and an ad-dition DC motor through communication withthe computer using an isolated serial line.

5) Sensor Interface: The GPIO functional-ity of Thor is implemented within the actusen-sor board. The board primarily communicateswith internal pressure, depth, and internal tem-perature sensors.

C. Sensors

Loki features one forward and one down-ward camera. The state of the vehicle is mea-sured using inertial measurement units (IMUs),compasses, and a depth sensor. To communi-cate with Thor, the hydrophone system acts asa receiving and transmitting acoustic commu-nication platform between the two vehicles.

1) Acoustic Communication: The acousticcommunication system enables acoustic basedcommunication/data transfer between Loki andanother vehicle (Thor). A single Reson TC-4013 piezoelectric element transmits and re-ceives acoustic signals. Loki’s hydrophone sys-tem contains the exact same implementation asThor’s, but the two extra receive channels arenot implemented.

2) Orientation: A combination of IMUs andcompasses measures the vehicle’s acceleration,angular velocity, and spatial orientation. Theorientation sensors on the vehicle are a LORD

MicroStrain 3DM-GX1 AHRS and a Spark-Fun MPU-9150. A Blue Robotics Bar30 High-Resolution 300m Depth/Pressure Sensor mea-sures the depth of the vehicle.

D. SoftwareLoki possesses an identical software stack

to Thor. Runtime-loaded configuration files en-capsulate the differences between vehicles be-hind a unified abstraction layer. Mission, vi-sion, control, navigation, and SLAM daemonslikewise run continuously on Loki. Our simu-lation engine can simulate the control charac-teristics of both vehicles, so that missions canbe tested on one sub or the other by changinga few configuration variables.

Loki’s lack of a DVL makes navigationdifficult. As a result, we use a more sophis-ticated velocity estimation algorithm based onsparse optical flow. First, features are detectedin Loki’s downcam using Shi-Tomasi cornerdetection. Next, the features are tracked viaLucas-Kanade optical flow. The bottom of thepool is assumed to be planar. Given the orien-tation and depth information from the sub, thefeatures in the image plane can be traced tothe pool floor. Their displacements relative tothe camera can be used to deduce the velocityof the vehicle relative to the pool floor. Newfeatures are detected periodically as old onesleave the view of the downward facing camera.

V. VEHICLE STATUS AND TESTING

Thor and Loki are both now in the pool test-ing phase. Prior to vehicle assembly, the me-chanical systems were thoroughly leak tested,and the electrical systems were bench tested.The first in-water control test took place in latespring (the end of March for Thor, the end ofApril for Loki). Testing to prepare both subsfor the RoboSub competition is still underwayin various Cornell aquatic facilities.

ACKNOWLEDGMENTS

CUAUV would like to thank all the indi-viduals who have supported us over the past


Fig. 20: Thor, as viewed from a GoPro cameramounted on Loki, at a pool test in progress

year, including Cornell’s MAE, ECE, ORIE,and CS departments, and Cornell alumni whohave supplied our team with needed lab space,materials, tools, and funding.

CUAUV would especially like to thank ouradvisers: Professors Robert Shepherd, BruceLand, and Ross Knepper; Director of Cor-nell Aquatics Fred Debruyn, the MAE Direc-tor of Instructional Laboratories Matt Ulinski,the Swanson Director of Engineering StudentProject Teams Rebecca Macdonald, CornellEngineering’s administrative staff, especiallyEmily Tompkins, Carol Moss, and MaureenLetteer, and last but not least the Cornell RapidPrototyping Lab (RPL).

We would also like to thank all of ourcorporate sponsors, without whom we wouldnot be able to compete:

Alumni Sponsors: Erin Fischell; SamFladung; Kenneth Bongot; David Hayes; JohnDiamond; Greg Meess; Leila Zheng; JamesRajsky; Tom Brooks; Kirill Kalinichev; JamesMwaura; Brian Schiffer; Nick Elser; DavidHinkes.

Platinum Sponsors: Cornell University;Monster Tool Company; SolidWorks;Nexlogic; General Plastics; BlueView;Mathworks; SEACON; Shell; AmericanPortwell Technology.

Gold Sponsors: Teledyne RD Instruments;LORD Microstrain; SeaBotix; Seaperch; Gen-eral Motors Foundation; Adlink TechnologyInc.; IEEE; AESS; SGS Tool Company.

Silver Sponsors: CadSoft USA; Intel Cor-

poration; LeddarTech; Molex; Advance EnergyInc.; iDS; ConocoPhillips; Lockheed Martin;PNI Sensor Corporation; Sparton; Allied Vi-sion Technologies; Surface Finish Technolo-gies; Exxon Mobil; General Electric; Bittele;Ximea; Advanced Circuits; Congatec; ShawAlmex.

Bronze Sponsors: Georgia Case Company;Adata; 3D Connexion; Sensata Technolo-gies; Digi-Key; Advanced Circuits; PolymerPlastics Corporation; The Mines Press Inc.;JetVend; Cayuga Xpress; MaxAmps; Pneuma-dyne; Domino’s Pizza; DIAB; Drexel Uni-versity; The Shelving Store; Asian Circuits;Fast Circuits; Lumeria Maui; O’Bryan Law;HomeFirst; RhinoShield; Sanford A. Schul-man; SkinBeautiful; TheImagingSource; FTDIChip; StudyPool; InkAddict; EMAC Inc.; Wall-side Windows; Convene; AAVID Thermalloy;Coupons.com.

Fig. 21: The 2015-2016 CUAUV team withThor and Loki


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