hell man get a gasser with out the motor thro in a large 12v motor form something like a starter, connect 2 12v batters to it and you almost good to go
all you would need would be the right gears connected to the motor and some sort of speed control witch you can probably use mechanical for that.
Hummm I have no idea if this would work or not probably need more RPM to get any speed out of it but.....
O dont forget about the heat this thing may melt lol
Starter motor:
http://www3.towerhobbies.com/cgi-bin...&I=LXJC35&P=ML
2X starter batteries in parallel:
http://www3.towerhobbies.com/cgi-bin...?&I=LXL370&P=M
anyway im not saying do this its more of an idea [8D]