Well, there's not really any efficient way to do it. those IC voltage regulators waste excess current to get to thier voltage, and at most thier rated for 1-2 amps (typically). You could try some intricate voltage dividers, or power supplies, but they would be too big, bulky, and expensive to fit in an RC car. If you're trying to use a 3 cell in a 2 cell ESC, just dont try. Buy a 2 cell pack, or get a 3 cell ESC. John.