[Al Skierkiewicz]

The data you logged is representative of the DC value of the output but not representative of the power delivered to the motor. The output of the speed controller is itself a PWM signal and only is a steady state battery voltage at PWM values of 0 or 255 when the speed controller is calibrated. All other times it is a pulsed DC output of varying width. The small voltage variations you see just outside the deadband are due to the very short pulses interacting with the complex impedance of the motor. The graphs linked by Joe Ross show current delivered to the motor which is more representative of the actual response of the motor.