2004.08_Robocup-a Look Behind the Scenes at the Robot Soccer Competition.pdf

Robocup

KNOW HOW

Robocup 2004 Goals!

Robot soccer gives you everything

you might expect from the real thing:

crosses, fouls, yellow cards – every-

thing apart from headers, in fact. The

players are autonomous robots with

Linux under the hood. Read on to

learn all about the technologies and

pitfalls involved.

BY GERD MAYER, HANS UTZ,

PHILIPP BAER

Gonzales are the four soccer

robots on the Ulm Sparrows team

that took part in this year’s Robocup Ger-

man Open [1]. This year’s open robot

soccer championship had a turn out of

150 teams. The Robocup [2] is an

research initiative designed to advance

robotics technologies, artificial intelli-

gence and image processing. Soccer with

autonomous robots provides a common

competitive platform and challenge.

The University of Ulm’s robot team

[3], first took part in this event in 1998,

and the team has been quite successful.

Although the team was the runner up in

2003, it did not make the quarter finals

in 2004. The champions in the Middle

Size League were the Brainstormer Tri-

bots, and the runners-up were Team

Persia from Iran.

Four a Side

Four robots per team play two 10 minute

halves on a pitch measuring 12 by 8

meters. Each team has a goalkeeper and

three field players. The ball is a normal

FIFA winter match ball in orange, and

the goals are yellow and blue. The pitch

is green with white lines. The robots are

allowed to communicate among each

other, but not to talk to external decision

makers, such as extra computers.

The pitches are artificially lit using stu-

dio lighting to provide constant, but

irregular lighting. As the robots can

travel at up to three meters per second,

and accelerate the ball at the same time,

the game can be quite dynamic.

This year, the Portuguese Minho

team’s defender headed off at full speed

into its own goal, narrowly missing the

keeper, while the forward attempted to

push the ball, and Allemaniacs Aachen’s

goalkeeper, over the goal line. Of course,

it was given a yellow card for that foul.

On the pitch, the referee had to jump out

of the way of a robot bearing down on

him at speed. The robot had obviously

spotted the orange ball in the ref’s

hands.

It was also a real pleasure to watch the

Aibos in the Sony Four-Legged League,

such as in the match with the Hamburg

Dog Bots versus the Microsoft Hell-

hounds, who were totally outclassed,

losing the qualifiers and the 3rd place

playoff 6:0.

At the Robocup, the robots have to be

completely autonomous. That is, they

are switched on at the start of the game,

and not controlled externally at any time

in the game – with the exception of the

half-time break where teams are allowed

to modify their robots (see Figure 1). The

robots look for the ball, hopefully find it,

turn towards goal, and try to score.

Research Problems

Of course, robot soccer is not the ulti-

mate research goal, but rather a testing

ground to investigate practical aspects of

robotics. The environment is dynamic.

Robots are expected to work with more

or less cooperative members of their

team, and to avoid the opposition. The

problems that arise in robot football are

similar to demands that occur in real life

– such as sending a robot to do some

shopping on a busy afternoon.

Gerd Mayer mainly works on the

robots image recognition and pro-

cessing capabilities. Hans Utz the

main Miro developer, and both are

Coaches for the Ulm Sparrows.

Philipp Baer is also on the team, and

takes care of the robots.

www.linux-magazine.com

August 2004

Autonomous Linux robots: The Ulm Sparrows Robocup Team

R oadrunner, Coyote, Speedy, and

KNOW HOW

Robocup

Figure 1: Before the game: The teams were busy re-calibrating their robots.

At the Robocup, teams that did not have laptops had to set up desktop PCs

on the pitch at times.

Figure 3: Under Gonzales’ hood: The lid (right) includes the holder and the

stepper motor for the Firewire camera, which you can see on the left-hand

side of the robot case viewed from the front.

Looking at the game in more detail

reveals topics such as self-positioning

and object recognition. The robot needs

to know exactly where it is on the pitch

to decide whether it should defend or

attack. Other important topics are activ-

ity planning, that is deciding what action

to perform at a specific point in time,

and coordinating the robots as a group.

The Robocup rules change from year

to year to force the competitors to con-

tinue development. Just a few years ago,

the pitch was surrounded by walls, now

the spectators stand at the touch line,

and that makes image processing far

more difficult.

The robots’ internal components are

attached to a CAN bus. The CAN bus is a

serial bus used by the automotive indus-

try. It can do without shielding and it is

extremely error tolerant. CAN also

allows components attached to the bus

to talk directly without bothering the

main computer. The CAN bus is con-

nected to the laptop’s parallel port by

means of an external controller.

the most part to allow elements such as

self-positioning to work in other environ-

ments such as in an office.

Our own robot middleware, a.k.a

Miro, is an abstraction layer for hard-

ware control. On the other hand it

provides various software frameworks

for robot control and video image pro-

cessing. Miro is based on Corba [4], and

that means that individual program com-

ponents can easily be distributed across

a group of computers. This is useful for

computationally complex tasks or

debugging. Miro is becoming more pop-

ular by the minute. It was released under

the GPL, and is available at [5].

Control & Image Processing

A complex project such as a robotics

application needs a well thought out

software architecture. It needs to work

independently of the robot hardware for

Robot Hardware

Our current robot, the Sparrows 03, rep-

resents the second generation of robots

designed and built entirely by our team.

The round shape proved to be a good

idea, as it prevents robots from getting

stuck, and so did the pneumatic kicker

with a compressed air reservoir that con-

tains enough air for a game. Figure 2

shows a schematic diagram of the cur-

rent generation of robots.

To avoid power problems, all of the

robots are run by a small laptop. The

robots’ main sensor is a Sony DFW V-500

Firewire camera. In contrast to analog

cameras with framegrabber cards,

Firewire has the advantage that it avoids

de-interlacing problems. Firewire cam-

eras provide a far better image when the

robot is moving and rotating. They also

have infrared distance meters, and rev

counters for their wheels (odometers).

Flexible Miro Modules

Another project uses the Miro video pro-

cessing framework and includes image

processing and object recognition tasks.

Forking into an independent project

makes it easier to use in different appli-

cation scenarios. The final module is the

soccer playing software. It includes

aspects such as world modeling, self-

positioning, and behavior patterns for

getting to the ball, kicking and so on.

Figure 2: The robots use IBM laptops (blue lid and

gray case) as their central computers. Below this

level, you can see the drive unit with battery

(gray) and the compressed air tank (purple).

Normal Problems

Robotics problems often have little to do

with the scientific objective. There is a

restricted choice of suitable laptops for

the robots. We decided to go for IBM

X31, IBM’s smallest models with 12 inch

displays. With a 1,4GHz Pentium 4 and

Centrino technology, which provides a

compromise between battery life and

computational power.

August 2004

www.linux-magazine.com

Robocup

KNOW HOW

This did mean having to cope with a

few issues concerning the Intel WLAN

module. With some assistance from the

Ndiswrapper project [6], and the Win-

dows XP driver, we managed to get the

Intel WLAN modules talking. The latest

version fixed the bug preventing IP mul-

ticasting communication. This was

important, as some software compo-

nents rely on IP multicasting.

Unfortunately, IP multicasting via the

Intel WLAN module seems to be quite

heavy on CPU resources. The load went

up to somewhere between 20 and 40 per-

cent whenever we needed to exchange

data using IP multicasting. The current

beta version of the native Open Source

WLAN driver by Intel [7] is not an

option at present. It consumed even

more CPU cycles in our lab tests. Fortu-

nately, there is a glimmer of hope, as

new versions are released every week.

there is something to transmit, the CAN

driver [8] eats CPU cycles all the time.

We decided to get in touch with the dri-

ver’s author, who immediately sent us a

new beta version. This allowed us to

migrate to the kernel 2.6 – we used ker-

nel 2.6.5-pre3-bk for the qualifying

matches. The preemption patches that

kernel 2.6 contains also meant a boost

for our system’s performance.

In contrast to consumer devices, the

Firewire cameras do not use libdv1394 ,

but libdc1394 or libraw1394 instead. On

kernel 2.4, the system had an exasperat-

ing tendency to stop in its tracks, and we

were unable to reproduce the conditions

that led to the error. In this state, it was

impossible to unload the kernel module

without rebooting the computer. This

seem to have disappeared with kernel

2.6, or at least they are far less frequent.

INFO

[1] Robocup Open 2004: http://ais.gmd.de/

GO/2004

[2] International Robocup homepage: http://

www.robocup.org/

[3] Ulm Sparrows homepage : http://www.

sparrows.uni-ulm.de/

[4] The Ace Corb (Corba): http://www.

theaceorb.com/

[5] Middleware for robots (Miro): http://

smart.informatik.uni-ulm.de/Miro/

[6] Ndiswrapper project homepage: http://

ndiswrapper.sourceforge.net/

[7] Centrino WLAN driver by Intel: http://

ipw2100.sourceforge.net/

[8] CAN Bus driver for Linux: http://www.

peak-system.com/linux/

to three meters per second. It will be fas-

cinating to see what the teams at the

world championships, May 27 through

June 3 2004 in Lisbon, Portugal, get up

to. Winning against the human world

champion soccer team by the year 2050,

is the goal that the organization has set

itself. See at http://www.robocup.org .

Future

There has been a lot of progress since

the first Robocup in Japan, 1997.

Whereas the robots were hardly capable

of moving, they now reach speeds of up

Power-Hungry CAN Bus

The CAN bus caused us even more

headaches than the WLAN. Whereas the

CAN bus only needs CPU cycles when

■

www.linux-magazine.com

August 2004

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