The original question was about pushing power without tripping. A few things to consider: multiple motors help, high mechanical power motors help (I.E. drill and Chips), gear ratio vs. wheel diameter is everything.
Basically, in order to guarantee that your breakers will not trip you have to do a couple of things. I will keep this post short, but you should download my white paper on drive systems located here:
Drive Sizing
You use the coefficient of friction between the surface you are driving on and your wheels as a fuse. You design your gear ratio and wheel diameter based on your motors working at 40 amps (for the drill and chip). Basically, take your weight * Mu * Wheel Radius and that is the torque at your wheels. Divide that number by the torque at the motor at 40 amps and that is the gear ratio you need to "slip before you trip". My paper takes into account efficiency, but this gives you the general idea.
One other thing. It is possible to get magic smoke without tripping. Breakers trip at 40 amps, but if you do not put enough voltage into the system (only push your joystick forward very slightly), then your stall current will be less than 40 amps. DC motors do not like being at stall because they use moving air as a coolant and if at stall too long, then the smoke will be released.
I know this is a simple answer, but look at my white paper and you will get all the detail you need.
-Paul