A controller connects the batteries to the DC motor. As the driver pushes down on the accelerator pedal, the controller delivers more power from the batteries to the motor. If the driver take their foot off the accelerator, the controller delivers zero power to the motor. The controller "chops" the volts thousands of times per second to create an average voltage somewhere between 0 and full power, in this case 120 volts.

The accelerator pedal hooks to variable resistors (potentiometers), and these potentiometers provide the signal that tells the controller how much power it is supposed to deliver.

The controller can deliver zero power (when the car is stopped), full power (when the driver floors the accelerator pedal), or any power level in between.