Yeah I agree, but I'm not talking about weapons:
You could allow every collision groups IF the pieces witch collide with C,D...I,J stay all IN the body of the bot and NEVER goes out.
In other words:
A bot is basically a body with wheels and weapons. The weapon(s) have to be operated with inner mechanism(s) (inside the bot's body). So the inner mechaism dont touch the other bot! It's always inside and protected. So who cares if this pieces collide with only A and B? I mean, it can collide only with J, doesn't matters, because it will never goes out (except in some fight case, I'ill talk about that later).
So the parts that really need to collide with A and B are: body, weapons and wheels.
The advantage of removing this restruction is that it allows more complex mechanisms -> more powerful/creatives weapons
and also in hard fight case : more complex mechanisms -> more weakness -> more disarmament opportunities for the advesary (if a bot punch very hardly, the inner mechanism can be broken
)
I could bring you some cool stuff if you deliver the inner mechanism from this useless restriction
EDIT:
I made one:
http://www.algodoo.com/algobox/details.php?id=91432Very basic. The only problem is that I increased restitution of the big red part and decreased on some other pieces. Not a problem, selec the whole thing and set restitution to 0.5