Review of Mobile Robot COlDpetitions

Thomas BriunlThe University of Western Australia, E&EEng., ClIPS

Nedlands, Perth WA 6907Australia

www.ee.uwa.edu.au/-braunl

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AbstractA number of international competitions formobile robots have been created and conductedduring the last 20 years. This article discussesthree of the arguably most prominent event seriesand their impact on mobile robot research,teaching, and media recognition. We willhighlight scope, rules, robot designs and robotevolution over the years for the MicromouseContest, AAAI Mobile Robot Competition andRoboCup and discuss their contributions tomobile robot research.

1 IntroductionMobile robot demonstrations always have a big impact onthe media, which of course in many cases is directlylinked to the availability of funding from university andother sources. More practically, robot competitionsprovide both a goal and an objective measure forperformance. This. should not be underestimated in aresearch area still looking for major industrialapplications.

Mobile robot competitions create student interestand inspire them to work dedicatedly on their projects.The practical solutions they find for all the smallproblems on their way will teach them more skills than alecture ever can.

But is it worth to invest much .tiJ'Ile and money in"just a student competition"? Can an actual researchbenefit be expected from these events or is it just to attractmedia attention?

2 Micromouse Contest"The stage was set. A crowd of spectators, mainlyengineers, were there. So were reporters from the WallStreet Journal, the New York Times, other publications,and television. All waited in expectancy as Spectrum'sMystery Mouse Maze was unveiled. Then the colortelevision cameras of CBS and NBC began to roll; themoment would be recreated that evening for viewers ofthe Walter Cronkite and John Chancellor-David Brinkleynews shows" [Allan 1979].

This report from the ftrSt "Amazing Micro­Mouse Maze Contest" demonstrates the enonnous mediainterest in the first mobile robot competition in New Yorkin 1977. The academic response was also overwhelming.Over 6000 entries followed the announcement of Don

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Christiansen [Christiansen 1911], who originallysuggested the contest.

The task is for a robot mouse to drive from start togoal in the fastest time. Rules changed somewhat overtime, in order to allow exploring the whole maze and thencompute the shortest path, while also counting explorationtime at a reduced factor.

Figure 1: Maze from micromouse contest in London 1986,displayed by EyeSim simulator www.ee.uwa.edu.aul-braunlleyebotldoc

The fIrst mice constructed were rather simple ­some of them contained not even a microprocessor ascontroller, but were simple "wall huggers" which wouldfind the goal by always following the left (or the right)wall. Some of these scored even higher than some of the"intelligent" mice, which were mechanically slower.

John Billingsley [Billingsley 1982] made themicromouse ... contest popular in Europe, while a realmicromouse craze was going around the world. Virtuallyall the robotics labs I know were building micromice in.one form or another. All of a sudden, people had a goaland could share ideas with .. a large number of colleagueswho were working on exactly the same problem.

Micromouse technology did evolve quite a bitover time, as did the running time. A typical sensorarrangement was using three sensors to detect any walls infront, to the left,·.and to the right of the mouse. Early miceused simple micro switches as touch sensors, while lateron sonar, infrared, or even optical sensors [Hinkel 1987]became popular.

While the mouse size is restricted by the maze'swall distance, smaller and especially lighter mice have theadvantage of higher acceleration/deceleration and there­fore higher speed. Even smaller mice became able todrive in a straight diagonal line instead of going through asequence of left/right turns, which exist in most mazes.

One of today's fastest mice comes from theDniv. of Queensland, designed by Gordon Wyeth (thereare still micromouse competitions held in 1999), usingthree extended anns with several infrared sensors each forreliable wall distance measurement. By and large, it looksas if the micromouse problem has been solved, with theonly possible improvement being on the mechanics side,but not in electronics, sensors or even software.

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Figure 3: Sample area for "call a meeting" task(from Kortenkamp's web site ~996)

Although the office navigation seems to have a remoteresemblance to the micromouse maze, it is quite different.The floor plan is known to the robots before they start, aswell as the rooms they have to visit. So it comes down toreliable driving without hitting a wall and correctrecognition of (open) doors and hallways. If this soundsalmost trivial - it is not, since it takes place in a near-realenvironment with the typical problems .of lighting,(sensor) reflections, etc.

modified earlier. The idea was to always present a newchallenge rather then leave one event for too long, so itwould not get solved easily. For AAAI 1996 in Portland,Oregon, the tasks were:

• "call a meeting"robots have to act as messengers by solvingnavigation tasks around a (mock) officeenvironment

• "clean up the tennis court"robots have to collect tennis balls from arectangular area and bring them back into a pen

Univ. Kaisers­er)

Figure 2: Two generations of Micromice flautem (photo Ralf Hinkel and Ewald von

.3 AAAI Mobile Robot CompetitionIn the end of the 1980s, the micromouse contest hadoutlived itself and the robotics research community waslosing interest. The problem was solved and did notprovide any further challenges. Around that time DavidKortenkamp initiated the AAAI Mobile Robot Com­petition [Kortenkamp et a1. 1993]. The first event washeld at AAAI 1992 in San Jose, California, where tenrobots competed in three events. These were:

• "roaming [a 22m x 22m] area and avoidingobstacles (cardboard boxes) and wandering judges"

• "searching for 10 distinctiv.e objects [three-inchdiameter poles] and then visiting each of the objects

• "timed race to of the objects found [inprevious task] and then back home"

While the AAAI competitions created new challenges,they were not as media friendly as the micromice ­basically because most of these tasks took about 20 min.to complete and the audience coul not judge whatprocesses and state changes were going on "inside therobots".

New tasks have been introduced over the years.Some competition events were kept over several yearsand only slightly modified, while other events were

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While "call a meeting" could be solved by usingsonar or laser range sensors, "clean up the tennis court"required the use of image processing in order to detectand track the tennis balls. "Squiggle balls" (balls with amotor inside to make them follow unpredictable paths)were added as an eXIta difficulty. Traditional planner­based progJ"8.U'lS can be used to solve the office navigationtask. The ball collection task on the other hand allows achoice of either planning or behaviour-based approaches.Newton Labs won this event in 1996 with a behaviour­based approach. The robot would just search for a yello~

tennis ball with its color camera, then rush towards It,grab it, and then.search for the pen area (marked by a bluebar) to return the ball. It did not make use of cartesiancoordinates and had no internal model of its position ororientation, although it would have been advantageous todo so. Other approaches, like Univ. Stuttgart [Briun} et al.1996], used a sweeping pattern or area covering approach,employing vision to catch individual stray balls.

Figure 5: Ball collecting robot from Univ. Stuttgart, IPVR

4 RoboCup"The Robot World Cup Initiative (RoboCup) is an attemptto foster Al and intelligent robotics research by providinga standard problem where wide range of technologies canbe integrated and examined. For this purpose, RoboCupchose to use soccer game, and organize. RoboCup: TheRobot World Cup Soccer Games and Conferences. Inorderfor a robot team to actually.perform a soc~er ga.me,various technologies must be Incorporated Including:design principles of autonomous agents, multi-agent ~ol­

laboration, strategy' acquisition, real-time reasonIng,robotics, and sensor-fusion. RoboCup is a task!ora·~eam

of multiple fast-moving robots under a dynanllc envIron­ment. RoboCup also offers a software platform forresearch on· the software aspects of RohoCup. " (from theRoboCup web site W'WW. robocup . org)

So robot soccer brings mobile robots to thespectator sport. Huge media interes.t.was. the result.afterHiroaki Kitano created this competition In 1997 [Kitano

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et al. 1997]. The competition actually comprises threeleagues at the moment:

• Small size league (max.. 18Ocm2 robot floor area)

• Medium size league (max. 2000cm2 robot floor area)

• Simulator leagueA planned large size league has been dropped, whilelegged robot soccer leagues and commentator leagues arecurrently being discussed.

Robot soccer teams play five-a-side soccer withrules that are freely adapted from FIFA soccer. Sincethere is a boundary around the playing field in both "real"robot events, the game is actually closer to ice hockey.The big challenge is now not only .that reliable imageprocessing has to be performed in real time, but also thatthe own team of five robots/actors has to be organised. Inaddition, there is an opponent teaD1which will change theenvironment (e.g. kick the ball) and thereby render one'sown action plans useless if one is too slow.

Figure 6: Robot Soccer Team CIIPSGlory UWA vs. Singapore

The small size league plays on a ping-pang-sizefield. It allows the use of extemal sensors, especially theuse of an overhead camera, which allows absolutepositioning of robots (own and opponent), ball and goals.Most of the teams so far· follow this approach, whichrequires a wireless transmission from the imageprocessing workstation to the robots. This led to thedevelopment of remote controlled units (one team actuallyused remote controlled toy cars) rather than mobile robotswith local sensors. Most teams have no sensors at all onthe robots and communication is a one-way broadcastfrom the ~orkstation to the robots. An exception is herethe robot soccer team from UWA [Braunl'and Graf 1998],which uses local vision and on-board computation withoutcommunication. .

The medium size league does not allow globalvision, so the participating robots are required to havelocal sensors and local intelligence (however, remotecontrol from powerful workstatians is still allowed).Many teams use off-the-shelf mobile robots ~ven .bylaptop computers. This makes it a costly exerCIse, .whIchnot all interested institutes are capable of fundIng orwilling to fund. In addition, the large field size of up to10m x 7m makes it hard for many teams to findappropriate practicellab space.

5 Research ContributionsOne of the frequent disappointments of robotcompetitions is that enormous research efforts are beingreduced to perfonnance in a particular event and cannotbe appreciated adequately. Adapting the home labenvironment to the competition enviro ent turns out tobe quite tricky, and many programs are not as robust astheir authors had hoped.

On the other hand, the actual competitions areonly one part of the event. Most competitions areembedded in conferences and encoura e ·cipants topresent the research behind their com tion entry, givingthem the right forum to discuss relat ideas.

At fIrst glance competitions seem to be anobjective measure for good research, but this is certainlynot true. Several aspects have to be taken into account.Are human judges involved, does a have a "homeadvantage" (e.g. the co tition environment being theirdevelopment/test environment), and how much is a team'sown rese ch effo 0 uch wasbou 10 mp 'esak rcomoneyalrese

• robot soccerti-robot I muerative

- co nica on- real time image- object identification- sensor fusion- plan~ng

• office navigation- planning- robust (sonar) sensor processing- obstacle avoidance- human-robot interaction

• ball collection- mechanics for ball collection- path planning- robust sensor processing- real time image tracking

I believe that all mobile robot competitions mentioned inthis paper undoubtedly brought progress to the field byinspiring the people who worked on it and bycontinuously pushing the limits of what is possible.Progress has been made through the competitions inmechanics, electronics, and algori . We have alreadyseen technology changes for the micromice. Starting withtactile sensors, improving with sonar sensors, and finallyreaching a near perfect state with optical line sensors andarrays of infrared sensors.

It is interesting to see that smaller robots tend toperfonn better. Not only because of obvious path

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advantages as for a micromouse being able to drivediagonally, but e.g. also for both AAAI'96 competitiontasks. Smaller robots have less mass and canaccelerate/react faster. However, they have thedisadvantage of much tighter payload and batteryrestrictions, which severely limit the sensor andco ting equipment that can be carried (unless wirelesstransmissions are allowed).

The simpler vision systems used for RoboCupare capable of performing image processing at a rate oftwo frames per second. These teams cannot competeagainst realtime vision systems with the PAL frequencyof 25 fps (50/2), while some. teams reach imageprocessing and command update frequencies of up to60 fps.

Micromouse and AAAI (so far) have been ratherstatic problems, which were basically "solved" at somestage. RoboCup on the other hand means playing anopponent, which will evolve as well over the years, so itwill hopefully remain in restin for quite a while.

other mobile roboter of newdesign an

ly valid researchis still fun to

a big opportunity for. interest and may

variou sources.inspir them to

.cal solutionstheir way will

a rogoalsa uapplica on to anumresearch topics.

However, we must be careful not to confuse acompetition with research. The objective for competitionsmust remain to interest students in a particular researcharea, to foster or initiate research for particularcomponents in mechanics, electronics or software, and tobuild a reliably working solution to a given problem. Acompetition must not be "l'art pour l'art", it can only bepart of a larger, well organised research program.

References[Allan 1979] Roger Allan, The amazing micromice: see

how they won, IEEE Spectrum, Sept 1979, vol. 16, no.9, pp. 62-65 (4).

[Billingsley 1982] John Billingsley, Micromouse - Mightymice battle in Europe, Practical Computing,Dec. 1982,pp. 130-131 (2). '

[Braunl et ala 1996] Thomas Braunl, Martin Kalbacher,Paul Levi, Gunter Mamier, CoMRoS: CooperativeMobile Robots S art, Proceedings of the ThirteenthNational Co erence on Artificial Intelligence, AAAIPress, Portland Oregon, Aug. 1996, pp. 1351-1351 (1).

[Braunl and Graf 1998] Thomas Braunl, Birgit Graf,Robot Soccer with Local Vision, Pacific RimInternational Conference on Artificial Intelligence,Singapore, Nov. 1998, pp. (10).

[Christiansen 1977] C. Christiansen, Announcing theamazing micromouse maze contest, IEEE Spectrum,May. 1977, vol. 14, no. 5, pp. 27 (1).

[Hinkel 1987] Ralf Hinkel, Low-Level Vision in anAutonomous Mobile Robot,.EUROMICRO 1987; 13thSymposium on Microprocessing and Microprogram­ming, Portsmouth, England; Sep. 1987; pp. 135-139(5).

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[Kitano et ala 1997] H. Kitano, M. Tambe, P. Stone, M.Veloso, S. Coradeschi, E. Osawa, H. Matsubara, I.Noda, M. A.sada, The RoboCup synthetic agentchallenge 97, Proc. of the Fifteenth Inti. Joint Conf. onArtificial Intelligence, San Francisco CA, 1997, pp. 24­29 (6).

[Kortenkamp et ala 1993] David Kortenkamp, M. Huber,C. Cohen, U. Raschke, C. Bidlack, C. Congdon, F.Koss, T. Weymouth, Winning .. the AAAI RobotCompetition, Proceedings AAAI '93, NationalConference on Artificial Intelligence, San Jose,California, pp. 858-859 (2).