[robocup-small] new ball.

[Beng Kiat Ng]

Hi James!

I thought the hockey ball were much heavier. Suprised that they can be chip
kicked 2/3 the field. I agree that unless the new ball is much better, it's
not worth the effort. And slowing down the ball without allowing down the
robot is not going to help.

One more thing. The current rules had been fine tuned for the goalf ball.
If we were to use another ball, many of these rules (like ball hold,
dribbling etc) might need to be changed. That's why we never succeed to
change the ball.

Regards
BengKiat



                                                                           
             James Bruce                                                   
             <bruce at andrew.cmu                                             
             .edu>                                                      To 
                                       robocup-small at cc.gatech.edu         
             19/09/05 04:57 PM                                          cc 
                                       Beng Kiat Ng <nbk at np.edu.sg>        
                                                                   Subject 
                                       Re: [robocup-small] new ball.       
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Beng Kiat Ng wrote:
> I proposed to use the hockey ball about 2 to 3 years ago. But it's wasn't
> popular as with any ideas that required teams to change their robots
> drastically. Seems that teams are willing to live with the problem of
golf
> ball, so long as they can use theoir current robots.

Our lab has been very involved in the dog league and its quest to
replace the no-longer-produced Sony orange ball.  Thus we have a ton of
potential balls around our lab ranging from ping-pong balls to half-size
rubber soccer balls.  We tested a couple variations of hockey balls last
Friday and we have a couple of observations:

(1) Dribblers work incredibly well on rubber balls.  Even with the
dribblers legal by the 20% rule for golf balls, the hockey ball stuck
extremely well to our robot.  There have been some outrageously
effective ball holding mechanisms in the mid-size league in the past due
to the soft and frictive outside of a soccer ball.  We'd have to change
a lot of rules and probably adopt some of the midsize rules to combat
overly-effective holding.

(2) For the lighter non-filled variety of floor hockey balls, we can
kick them all the way across the field without the ball touching the
ground (with a regular forward kicker).  I'm not sure that's what people
meant by slowing the game down.  Obviously it doesn't move as fast as a
golf ball would, but it's not really more controlled.

(3) For the liquid-filled damped hockey balls, we can still drive them
2/3 of the field in the air, and they hit the ground like a brick.  Chip
kicking these might be a little too effective, as you need not reason
about bouncing at all.  It flies through the air, and then just rolls.
It's true that its a slower, but chipping is easy due to the large
relative size of the ball... all teams already know how to build a
kicker that's only 2cm from the ground.

And now for my opinion:
Taken together, if we improve dribbling effectiveness while slowing the
ball, it seems to me it will discourage team play.  That is, unless we
restrict the robots' top speed at the same time (which seems to be
unpopular and difficult to enforce).  I do think that kicking power is
getting a bit silly, but really the >=5m/s kicks are what made passing
preferable to driving a ball somewhere.  If we're worried about
ref/crowd safety, we should just make those rules more explicit and
enforce them.

That said, I *do* like the idea of exploring other ball options, but as
in the dog league, a new ball has to be a lot better for it to be worth
the disruption of switching.  It'd be really nice for people to bring
example balls to RoboCup and demo them to the other teams.  I think
that's the best way to convince a majority of teams that a new ball is
indeed better.

Jim Bruce
CMDragons/CMRoboDragons