Both resistors and transformers will define the final drive speed of a motor. To the equation of FD = r * V Where: FD = a made up value for the rpm of the motor shaft. r = resistance (standard) V = Voltage (standard) The motor is spinning at a speed dependent on the over all "power" (watts) it receives/uses. It will want to "use" all power available, to an extent. To control the 1.5V fan, firstly check you are correctly supplying 1.5V, then add a variable resistor to the circuit (calculate which values you need, and buy it from an electronics store, ones with Dials are called Potentiometers, or "Pots"), this will give you a dial to change the resistance, therefore slowing down or speeding up the motor. You could also add a fuse to the circuit for a specified Wattage, determined by the max power you want the motor to use. If the motor burns out, it reduce it efficiency and effectively need more energy to spin at the original rpm, which with blow the fuse if correctly calculated. Capacitors are not necessary, however a diode is needed to convert to DC, but your transformer should do that for you. Good luck with the 'lectrics.