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Design of a Small, Chea p UUV for Under-ShipInspection and SalvageDavid P. MillerIUPRReston , VA 22091

Phone: (703) 620-0551. FAX: (703) 860-1802eniail: k i p ;s rc .umd edu

AbstractSriiall UTJVshave a wide variety of uses including in-spection, ins truInent placement, specirrlen gatheringarid salvage. However the uses of these UUVs has beenlimited by t,wo factors:1. Cost ~ UUVs llave heen traditionally quite expen-sive, puttirig tklerrl well out, of the reach of the tra-ditional marine ogerator.

I o need for real time videoThe last three item s above are unusual for a,UUV.

Alm& all UUVs rilIi a t,et,her back to the surface forsending \-itleo,rcceivirlg commaIlcls, and oftenpower isrim over the t ether as well. However, if a task doniainis chosen where real t,ime commands and video are riotneeded then the tether can be eliminated. The onlychallenge that remains is controlling the robot without

2 . Wires ~ ?r4ost,UUVs trail a cable for power. control,a n d video back to t he operator. The cable makes itdifficult to use t,heUUV in kelp, or in the presenceof net,s or other UUVs.

This paper describes the design and function of a small(lcss tliari 10kg) arid inexpensive UUV that is given amission clesrription and t,hen carries ou t that niissionaiitonorriously. Thc UUV can home in on a beacon.assuring its recovery at the end of t,hr mission. Thisvehicle can be used for everything from inspecting afouled propeller to placing a piece of equipment on theocean floor in tlie middle of a kelp forest.

IntroductionUUVs are used for a variet,y of tasks that require awide range of capabilit,ies. Th e syst,ems that have beenconstructed arc t,ypicaIly fairly large' and expensive.In part, t>his s due to thc large number of capabilitiesthat, are built, into t,hr: vehicles.It, is our belief t,liat a useful UUV could exist. thatwould have a very 1iniit)ed set of operating capabili-ties, and that a UUV t,liat met those capabilities couldbr prodiiced at relat,ively low cost. Thr limits we arescttirig for th c purposes of this pap cr are:0 Shallow water (dept,hsof less than 30m)

Calm wat,cr (currt.nt,s of lcss than 2 knots)0 Clearly defined mission goals0 Low costo No ntwl for real time c~onimancis

'while rriosl TJVVs arc srriall when compared t o st,aridardsubmersibles. they ar e larger and certainly heavier thanmost mobile roboh.

continuous telemetry.Fortunately. behavioral cont,rol technology [a]hasadvanccd to the point where autononious cmitrol c;an

br added to a UUV. and is sufficient for carrying outmany types of nh si on s. Behavior control has beeniiscd successfully on UUVs before, but in [ l ] i t wasused to safe the vehicle from collisions, and in [3] it wasused to control a legged bot tom crawling vehicle. In [4]behavior control was suggested as part of the overallarchitectiirp in a much more complex UUV.We are u11-aware of a n y work t.o use behavior coritml to minimizethe sizc and cost of a UUV the way it, has becn 11sedto niininiize these factors in o ther types of explorat,iorirobots [SI .The types of niissions we will address with this sys-tcni are simple inspection of a well defined area, suchas tlie hull of a ship, or simple rendezvous with a welldrfined target. I n both instances, well defined meansthat tlir target or hull itre readily detectable by thesensors oriboard th e vehicle.No attempt is made in this system to keep tra,ck o fthe robot's absolute position, or to follow a specificcourse tluririg the mission. Th e targetas arid areas ofinspection are dc4ried by their visual characteristics:brightnrss arid color. or t,heir contrast to t,he rest, oftlir mvironnient .

The VehicleOur x-eliitlr DRIP' is 44 5cm in length has a riiclx-imum tliamcter of 12 cn i and displaces 3.81 o f water.Like all of KIPR ' s robots, tlir use of off the shelf parts

0-7803-3 185-0/96$5.0001996 IEEE

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are rnaxirnixd to incrc reliability and reduce cost(sec, [5,7]) . 1 from PVC sewerpipc antl a 12v divr light. Th e resulting structure isshown in Figure 1. This combination of parts allowsmilch of t h e hull to hc disassembled for cleaning aridniaintenance. The dive light casing allows easy accessto tht: electronics antl b atteries th rough th e uriscrew-able lcxan hexti1 at,the front. Th e three posit,ion switchfrom t,hr light has htwi utilized to act as a main pow-er antl corriputw reset, switch. The clear lexan frontallows thc seiisors to have a clear view of the environ-ment.

The hull o f D R I P is constriic

Figure 2: DRIP'S Propiilsion Pump

Figiire 1: The D R I P UTJVThe propulsion arid steering systcm is provided bya set of rnodel airplane refueling piimps. shown in Fig-

ure 2 . These in-line, reversible pim ps a re used to moveth e vchicle forwards arid hckwards, as well as control-ling yaw.Pitc4i is cont,rolleclhy c~hitriginghc: C G . A wciglit isniovt:tl along the insitlc of the vehicle by a nioti.)r aridball scrccw arrangcmcnt. The vehicle is weightcd tobe rieutrally biwyant (a very sliglit, positive buoyancy

is niai rita iwd) Depth is cont,rolled by altcring pitchantl thrust,iiig forwarcl or in rcversc. Approximat,cdhovering ('anbe maint,ained by riiaint,aining a slightpitacharid tliriistirig forward and hack its needed.

Power is supplicd 1)y four st,antlard 1. 5aH- 7. 2~i-cad hatt,ery packs . Thr. niotors ire operat,t:d at ap-proximat>ely1 4 voks. Tlic power for t he electronics isregiilated at 12 volts.

On-board coniputation is siipplietl by a Vwta 68332or hoard (Figiu-e 3) running tlie ARC real-timeoperating systcrn. Tlic proccssor corit,rols t hc. piimpsand motors throug h a relay board. Spw d control of themotors has not t ) c m i inipleriierited. However speed o ft,hc veliirlc ra n h ( 3 (witrolled by tlw n i i r r i k r o f piinipsthat, have htwi m g a g d .

Figure 3: The Cogiiachrmnr. Color Tracker mountedfudihfd- mh.

The stand ard sensor suite for D R I P consistJsof an ar-ray of photo t,ransist,ors, ancl an IR proxiniity sensor.Additionally, there are several proprioceptive sensorsfor nionitoring thc intcrna l :stat

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Figurc. 4. The color carnera (3.5 floppy in backgroundfor sc.alr)

ed. Tlic first full-up systcrris tests in tlie vater shouldtake place in th e next few wecks. The testing will takeplace in a. local neutral biioyaricy tank which is fiftyfeet in diameter and t,wenty-five feet deep.Once t,lie syst,eiii is fully operat iona l; we plan to testDRIP in a vitrict,y of scenarios including:

Find the dive light,. In t,his scenario the rohot searchcs ou t a dropped dive light arid rendezvous with i t .This is a preludc to a salvage task .Follow the diver. The robot tracks the cdors ofa partic:ular divcr and follows them around whileavoiding ot,her divers and ol)ject,s.Hide iinder t,lit: boat. In this scrriario; t h r robotstays near but iiritlcr a boat or other platforrii or1tlic surfacc. This is a prelude to a hiill inspectiont,a.sk .The narts costs o f t,lie mrriDIete veliirle are iintlcr$3000. Approxiniat,cly two-t,liirds of that cost goes to

the color t,rwkiiig system. If low-cost srnsors ran tirfound for iispfiil niissioris, then copies of D R I P coiildtic reproduced at alrriost disposable prices.

ConclusionsSonic UUV opcratioris c m tw dorir without c-orit in-iioiis opt:rator iritcrxmt,iori. Oricc this asmiliption isniadr, thc unibilicd that follows alrriost all UUVs cantw cu t , frc&ig t h e . UUV. arid eliminating rr i i i c l i of tliroverliead of both t,hr UUV arid its optJrations. il serrii-autonorimus UUV can b c xist,ructed for very low-cost .We hope to prove over thc ricxt scverill rnonths thatsuch a, TJUV will liavtl liigli util ity.

References[I] Irtrr f b o . 1rndrrwater Expt~rirntmts - s i n g li rip-act,ivclSysterri for Autoriorrious Vc~h~cles.n the Irocrcil-

h g s of th e 1991 National Conierence on Arti f icial htel-iigence. j1.4A1 pgs 794-800, July 1991.[Z] Rodney A . Brooks, A Robust Layered Control Systemfor a Mobile Robot. I E E E Journal on Robotics an d Au-t om,a f ion .vol R.A-2#1. March 1986.[3] H. Greiner, et.al., Autonomous Legged 1TnderwakrVehicles for Near Land Warfare, i n Proceedings of t h ~untermeasures Sympo-[4] Shller. D.P . . 6, Slack, M.,G. , Design & Testing of aLow-Cost Robotic Wheelchair, in Av,tonmmous Robots,

volume 1 #3 . 1995.[ 5 ] Sliller. D.P.. Slack, M.G., & Elsat,sser, C.. Ari Irnple-mented Intelligent Agent, Architecture for AutonomousSubmersibles, in the Intelligent Ships Sympos ium Pro-ceedings: Intel l igent Ship Tecfmologies o r the 21st Cen-t w y . June 1994.[6] 1,JilIer. D. P. .lesai, R.S.; Gat,, E. , Ivlev, R., Loc:h. J. ,Reactive Savigatiori Through Rough Terrain: Experi-mental Results. in the Proceedings of the I992 NationalCorifewnce o n z4rlzfiicialIntelligence, pp. 823-828, Sari

.Jose. CA. July 1992.ilstein,