Greetings Graham,
Welcome to the FRA forum. The bot you refered to at Debenham was ours, Scorpion Jr.
If I may offer a little advice. First, before you pick up any tools, think carefully about what you can realisticly hope to produce given your abilities, the facilities and materials you have available.
If you have an intrest in building a spinner, be VERY careful, and be certain that what you propose to build is safe. It is not just a case of spinning a big mass, you need to understand the forces involved and be sure that what you are supporting that spinning mass on is strong enough. For example our disc only weighs very slightly under 2Kg but it is suported on a 20mm dia. solid stainless steel axel suported by heavy duty flange bearings mounted in a frame made of 6082 T6 grade aluminium. If you think that is a bit OTT for a feather, consider the energy required to cut that spike clean off PLF and launch it across the arena with enough force to damage the makrolon screen. In doing that, our machine was subject to an equal force, so you need something strong enough to absorb that kind of energy no just once but time and time again. If you get it wrong and your design comes appart in the arena the only thing that gets hurt is your pride. but if it comes apart in your garden shed when you are testing it....!!! Even an average featherweight spinner is more than capeable of inflicting a very serious or at worst a fatal injury.
Im not trying to put you off building a spinner but please think about what is involved. you may do far better by buliding a simple push bot first off, bring it to a couple of live events enter in a friendy whiteboard fight or two and see how you like it. But if a spinner is still the way you really want to go, remember that if there is ANYTHING that you are not sure of just come to the forum and ask the question, there is a vast amount of know-how out there in the roboteering comunity and we are always willing to share it.

Good luck and safe roboteering,
Geoff,
Team Scorpion.