The power needed to accelerate 12kgs of bot around the Arena at a competative speed of 8 mphish is I guess going to be around 360 watts peak....

Your running 12 volts so youll perhaps be pulling around 30 amps PEAK.

The maths say that youd pull 1/2 the amps ( 15 amps ) with suitable drill motors geared for the same speed running on 24v.