Rampaging chariots

[makspll]

I'm participating in the Rampaging chariots event in June. basically they give you a kit, and you have to build a robot, which is then supposed to either participate in robot sumo, tug of war and then in football and an obstacle course race.
here is the construction manual with all the specs: http://www.rampagingchariots.org.uk/construction/rampaging-chariot-manual-2015.pdf
and the rules: http://www.rampagingchariots.org.uk/games/rampaging-chariots-robotic-games-rules-2015.pdf
could someone guide me on what power transmission should we use to get the torque needed to push a 12 kg robot that is pushing aswell, out of the ring.
we also wanted to transmitt the power onto all wheels (4x4 drive)
we also want to add a scoop, front wedge to lift enemy vehicles easilly at sumo.
also maybe adding tank tracks would be useful
could someone guide us ?