Don't think there is Dave, not yet anyway. I think it's pretty much a case of weight being the biggest size restraint. However (I'd need to read through the posts again to check) I think the arena is something like 2m square so as long as it's smaller than that you should be fine. What's your design like? Or you keeping it under wraps until it's nearer completion?

EDIT: Wow, this topic's up to 16 pages already? Quite impressive for a class that hasn't fought yet