Thanks guys, much appreciated. Just hope it performs better this year!

I've just weighed the robot in its completed state and it's coming in at 11.3kg
So 2.3kg to spare and nothing more to do to it. Could possibly increase the thickness of the armour after the champs, but I don't think that would provide much of a benefit. Other option could be to try and pack more weight into the drum.

The plan is to go back to a four-tooth drum after the champs, so my best bet would be to increase the thickness and diameter of the teeth to try and bring the robot closer to the weight limit (while maximising damage potential of course )

Anyway, I'll be taking it to work tomorrow in the hope that I'll have a few spare minutes to test it out. Test subjects will probably be some old drawers and cupboards (maybe some aluminium rail) so nothing hugely challenging, but that's all there really is available. Video should follow within the next day or two...