Originally Posted by raymor

For those curious about electric motor RPM and why gears are needed, a motor and a generator are basically the same thing. When a motor spins, it generates electricity backwards from the way the electricity from the battery is coming. So in other words, a motor being run at 6V acts as a generator producing -6V. That's why it can't go any faster than that max RPM - the negative voltage it generates depowers itself. So with 6V + -6V = 0 volts, the motor has basically no power at max RPM. On the other hand, a motor at 0 RPM obviously isn't moving the car. So you want to keep the motor RPM right in the middle of those two extremes, at half of max RPM.