[robocup-small] Proposal for energy budget

[Michael Babish]

> A lighter ball, unless it is really light like a balloon, will travel
> faster. It is also likely to be weaker and easily damaged by the
> contending robots.

What about the small plastic ball used by the dog league?
What about the real-sized soccer ball used by the mid-size league?

Personally, I don't like limiting the physical batteries.  I'm not
convinced that it will solve the problems with overcrowding on the field. 
And I think it will introduce new problems.