[KenWittlief]

the deciding factor (as Don Rotolo alluded to but did not completely explain) is the inertia of the whole robot.

If you look at the current vs RPM specs for the motors, the stall current with 2 or more motors can be more than 150A.

The real question is how fast can you accelerate your whole robot, so the motors will get up to an RPM that will not trip the breakers?

If the drive train is geared way up it will take several seconds for the robot to get from 0 to 1mph, and by then your breakers will have already tripped.

Even if your drivetrain can overcome the static friction, if you cant get the motor current down below 40A within a second or so, the breakers will trip - thats the limiting factor. It all boils down to F=MA, the force being the torque of the motors, and the Acceleration needed to get them motors up over their 40A part of the current/rpm curve, within a second or so.

If you use the static friction of the drive train as the controlling limit, the robot may be able to move, but it may not be able to accelerate fast enough to keep the breakers from tripping.

I cant give you a specific motor torque, because it depends on the weight (mass) of the robot, and the resistance of the drivetrain (narrow hard rubber wheels vs tank treads....)