[robocup-humanoid] "Size 1" Soccer Balls

[Sean Luke]

I'm wondering about the possible variance in soccer ball size for the kid-sized league: for small robots such as the Darwin-OPs, a cm difference is significant as the robot arms could touch the ball.  

The humanoid league stipulate a "FIFA Size 1" Ball.  Is there an official FIFA size standard for size 1 balls (indeed, googling for "FIFA Size 1" just gets RoboCup humanoid pages!).

We have purchased six "size 1" mini-balls, all purporting to be official, and they vary by as much as 50% in size.  Additionally, some googling reveals a variety of different claims:

http://help-en-us.nike.com/app/answers/detail/a_id/54000/~/soccer-ball-sizes
	"18 - 20 in, 45 - 51 cm" circumference

http://www.buzzle.com/articles/soccer-ball-sizes.html
	"does not exceed 17in (43 cm)" circumference

http://www.deptfordsoccerpost.com/2012/05/01/what-size-soccer-ball-does-my-child-need-this-year/
	"17 inches in circumference" (43cm) circumference

http://www.answers.com/Q/What_is_the_circumference_of_a_size_1_soccer_ball
	"18 inches (approx. 46 cm)" circumference

http://www.soccer-academy.net/soccer-ball.html
	"Usually no more than 17 in (43cm)" circumference

All of these answers seem to be at odds with the Humanoid League rules, which state that the ball is "approx. 13cm" in diameter, or 40.84cm (16 in) in circumference.

There is a big difference between 16 inches and 20 inches in circumference.  Can this be narrowed or qualified?  What diameter range should we be expecting?

Additionally, it seems that FIFA permits an amazingly wide range of inflation pressure: 8.5 - 15.6 psi.  Given our recent NFL scandal :-), and the fact that pressure differences have a *big* impact on small balls due to the large sizes of the seam material relative to the ball, is there an inflation standard we should be expecting?

Sean