**broken link removed**
Are you joining in this type of games? Well, terrible.. it's really a warrior robot. I've never take part in that type of games, but I think the main problem is that building mechanical weapons. And strengthen the torque of motors with given weight of robots.
May you explain your purposes or the games, because i'm in mechatronics (meca - electronique - en francais), I also have some knowledge on mechanics.
By the way, to strengthen the torque on the wheels, do you have to turn your robot around? or just go straight forward? You should build your robot like a tank. Connect the active wheels and passive wheels with wires.
Of course, you always need gearbox to increase the torque of motor shaft.
Anyway, as you will see how a small chicken can win a cock on fighting, it's a traditional military art of my country. It's because the chicken move fast around the cock and it hit on to the weak point of the cock. In this case, you don't have to get strong torque but low speed, you make your robot run fast and use multi sensor to detect the enemy, and always get behind him. Go after him in all case, you can hit him, but he cannot. Or you may see when he hit you with sensors, and move away from dangerous places..... etc..