Hi,
You can control an analog motor by implementing a PWM signal (where the speed of the motor is determined by the duty cycle of the signal). So you can just set a duty cycle greater than 0 every time your ADC read is greater than a certain level.
PS: I recommend you first check the frequency you would have to configure the PWM so you can have the maximum speed when you set the duty cycle to 100% (You can try this by trial an error of the insertion of different PWM frequencies or you can check if this information is already provided for the motor you would be using).
Best Regards,
Ricardo Delsordo