[robocup-humanoid] [robocup-nao] ball decision for 2010

[Tekin Mericli]

Hi Oskar,

On Sat, Dec 12, 2009 at 1:11 PM, Oskar von Stryk
<stryk at sim.tu-darmstadt.de>wrote:

> Hi Tekin,
>
> As you probably know, the RoboCup Humanoid KidSize League uses
> an orange standard tennis ball.
>
> To my (limited) knowledge, the standard data for tennis balls are
> - diameter: between 6.35 und 6.67 cm
> - weight: between 56.7 und 58.5 g
>
> The data you mention for an orange street hockey ball
> (65mm in diameter and 55g weight) matches the
> above data of an orange tennis ball pretty well.
>

You are right, the dimensions of a street hockey ball are very similar to
that of a tennis ball. Let me try to answer your questions below.


>
> Therefore I was wondering about the following:
>
> 1) Why did you select a hockey and not a tennis ball
>        as it is used in the Humanoid KidSize League?
>

We had some discussion about whether switching to a tennis ball after the
original ball would be a good idea. You are right, tennis balls are common;
however, they have a lot of variance in how they are made (fuzziness,
weight, color, etc.).  Thomas pointed out that the orange tennis balls are
relatively tough to get - I think they are only available from a dealer in
Canada. On the other hand, the street hockey balls are available (almost)
worldwide and they have very similar texture characteristics.


>
> 2) Did you compare the performance of the hockey ball
>        with a tennis ball on a RoboCup soccer field?
>        And, if so, what were the results?
>
>        (Besides size and weight, tennis balls must satisfy certain
>        back-bouncing abilities from the ground and will probably
>        behave differently than hockey balls in robot soccer.)
>

Yes, the performances of various balls including our old ball, tennis ball,
street hockey ball, and juggling ball were compared in terms of visibility
from longer distances, rolling straight, rolling distance, and amount of
back-bouncing. Since the street hockey ball can be seen fairly well from
longer distances, rolls straighter compared to our old ball, does not bounce
that much so that incoming ball control would be easier, and being easily
available worldwide, we decided to proceed with the street hockey ball for
now.


>
> 3) If teams order a standard orange street hockey ball from
>        a store which does not give the precise diameter
>        and weight of the ball, which range of variation
>        in size and weight must be expected?
>
>        From a quick internet search it seems that there
>        is more variation in street hockey balls than
>        in tennis balls. I found: diameter 6.35-7cm, weight: up to 85g.
>
>        A weight difference between 55g and 85g can make
>        an enormous difference to the robot performance (e.g.
>        when kicking the ball)!
>
>        In the Standard Platform League where only software should count
>        I would expect also a standard ball that teams can, e.g.,
>        remotely participate in local RoboCup Open competitions.
>        With a large variation in ball weight, this will be difficult.
>

We pointed to some certain brands, so the balls you get won't have any
problems if you specifically look for those brands or if you find another
brand and ask the store about the dimensions to be sure before you purchase
them. One such brand is Mylec:

http://www.mylec.com/mylechockey/Products/tabid/102/Default.aspx


>
> Thanks for your time and efforts.
>

You are very welcome.

Cheers,

Tekin
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