Robot wars is not, actually, a contest between robots. That is, the 'robots' used in the competition are custom built remote-controlled vehicles, mostly wheeled. They do not make any decisions for themselves. There was an attempt to introduce a class of autonomous vehicles in the contest I went to (Summer '96), but it wasn't very successful. Hopefully future autonomous competitions will do better. That said, Robot Wars is still an extremely exciting and interesting constest, at least to a gearhead like me.
Destroy All Robots
Robot Wars pits two robots (generally) against each other in an arena. The objective is to immobilize the opposing robot. A robot is considered immobilized if it does not move for 30 seconds. A robot can immobilize its foe by damaging it enough so that it is unable to move or by flipping it.
More Rules
Competing robots are split into four weight classes: Featherweight (0-25 lbs), Lightweight (26-50 lbs), Middleweight (51-100 lbs), and Heavyweight (101-165 lbs). Robots fight for the championship with their own weight class. There are restrictions on what types of weapons can be used. No liquid, electric, or explosive attacks can be used. Any projectiles must be tethered. Attacks are thus generally restricted to brute force, such as saws, hammers, and drills.
The arena itself is a a force in the competitions, especially in the lower weight classes. There are traps and moving obstacles which can restrict movement or even damage robots. I witnessed many bouts in which the arena was a major factor.
Matches themselves last for five minutes. At the end of that time, if both robots are still mobile, or if they have become equally ensared in each other, the outcome is decided by the audience through applause. This does happen, so it can pay to try to make a robot seem 'cool'.
Interested?
If you're interested in competing, all I can say is don't be intimidated. My partner - Rob - and I built a decent robot with no robotics or even R/C experience. It can be done.