Thanks Shakey. The counterweight idea came when I saw there was a 100kg limit, so I thought 10/20kg on just the internal weight would be enough to counter movement. If I scale it down, it'd be no more than 500g so it's pointless. I may however build it without the weight, just to see if the idea would work.

I'm not sure of the bamboo either. I'm basing that idea on when I used to watch Robot Wars and the robots would be built from scaffold poles. Then I remembered bamboo is used for buildings, scaffolding etc. It is strong, however it could split under impact. But I think that's a trial and error process, depending on the diameter and the thickness of the bamboo. Besides, if I use HDPE I'd have to change the name to "The Big HDPE" :P

The wiper motors I bought come with a bit of a gearbox I think - I haven't stripped them down. I'll try out the wiper motors as I've got them, but I can switch to the cheap drills if I struggle with them.

And thanks for the advice. In the space of a week I've gone from cramming everything to get an application in to RW through to reducing the size of the robot with a view to doing local events that I didn't know exist. It's a bloody lovely learning curve this is and just keeps getting more interesting.