GEERHEAD
For the dogs to recognize
the ball’s new position when
placed by the referee, the
programmers added rules to the
EKF that basically tell the dogs
that the ball is able to teleport
to standard field locations once
it has gone out-of-bounds. This
enables them to easily locate the
ball again after it has been
moved by the referee. This
feature enabled the Northern
Bites robots to get to balls
positioned by referees 85 out of
127 possible times.
Soccer Moves
This image shows two boxes with parts
from a disassembled Aibo and additional
parts in white in the background. The
Northern Bites team had to remove all these
to get at the robot’s neck, to remove it.
The basic moves for a
Soccer-playing Aibo include
walking, kicking, and running.
The Northern Bites team uses a
walk engine to create the variety
of joint angles needed to get the
robot to walk or run as desired. The
Northern Bites programmers looked at
walking or running as the movement
of the robot’s foot through space.
In that way, they can think of the
movement as a shape like a trapezoid.
By using an inverse kinematic system,
the walk engine tells the programmers
how to set up the dog’s joints so it
can make those shapes and walk or
run accordingly. The roboticists feed
this information into a machine
learning system. This enables
the robots and programmers
to learn the best shape of the
curve for the foot to make
and how fast it should move
through that curve for optimal
walking or running.
To kick, the dogs trap the
ball under their chins and
draw it back to their chests.
“From there, most kicks
consist of the dog using its
two front legs in a kind of
chopping motion to knock
the ball forward,” says Chown.
The team uses a method in
which the dog runs at the
ball as fast as it can and
grabs the ball under its chin
in one motion.
Not from Sleepy Hollow, but a headless
Aibo none-the-less. On its back are silver
touch-sensitive LEDs. Inside are its
motors and microprocessor.
rest of the team based upon relative
positioning. Our positioning and
teamwork is what won us the world
championship. Though we were no
faster than any other team, we got to
loose balls about two out of three
times against the best teams (and far
more against weaker teams),” says
Chown. When the ball goes out-of-
This is another disassembled Aibo with the
neck removed. The gearbox was at issue
here, which the team was trying to repair.
It is lying left of the Aibo’s head. A
workbench with tools and instructions for
dismembering Aibo lay in the back.
bounds, the referee places it inbounds based on where it went out
and which team knocked it out,
Chown explains. This is because the
robot dogs can’t actually throw the
ball in, as regular Soccer athletes
would.
The Northern Bites dogs use
an Extended Kalman Filter (EKF) to
estimate the ball’s position. This
becomes especially important when
determining position after the ball
has been placed back in bounds.
Here you can see the neck joint under repair.
In the middle of the neck, on the light gray
plastic is a fitting that connects the gear above
the neck. The fitting has begun to erode. The
team used epoxy to strengthen the connection
between the gear and fitting.
12 SERVO 05.2008
