http://www.youtube.com/watch?v=BsC5gON85Uw

I dont know about doing too much damage, but it deffently gets everyone on your side. And its a lot of fun.
I wouldnt want to use a bigger motor. Youll either end up with the current draw being too high or putting in too much torque and not being able to keep your robot on the ground. Lighter weapons would fix that but then you wont be doing as much damage or be as entertaining.
And Ive found that hammers do more damage then axes or picks.