Slowing down an electric motor?

I am working on getting all the supplies together for my first instructable.  The item I am building (not giving out many details) will have 5 different motors on it.  I think all motors will be the same model.  However I want one motor to run quite slower.  Can I do this without having to run it off a lower voltage power supply.  Now that I think of it I suppose there is plenty of room in my item for a 2nd power supply.  But this will still be good information for me to have in the future.  Oh and the main power supply for the item will be either 3 - 6 volts I believe.  AA batteries in case this matters at all.  Thank you in advance for your help in this matter.

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jcaresheets (author) 6 years ago
Oh and something I do not understand however is this. If I have a remote control car and the batteries start to wear out, the car goes slower. So why will decreasing the voltage not decrease the speed of the motor?
It will.
.  It will (in many cases).
.  Most motors and solid state devices are most efficient at two points: 0% on and 100% on. When you lower the voltage, the motor is less efficient and generates more heat. Same with the electronics that drop the voltage. The PWM that kelseymh mentions pulses full power to the motor, so that the average voltage is lower, but the motor/electronics are always either full on or full off.
jcaresheets (author) 6 years ago
Thank you everyone for the replies. I am not sure where I am going to find a slower motor. I need 4-6 motors that all run at the same speed and then one motor that runs at like half the speed or maybe even 1/4 the speed as the others. I will start studying how to do this.
kelseymh6 years ago
So these are DC motors. You don't control the motor speed by changing the voltage; rather, you do it by turning the current on and off very rapidly (hundreds or thousands of times per second). This is called "pulse width modulation", and is the same technique used to "dim" LEDs.

If you search for "DC motor controller" or for "PWM" you'll find lots of commercial products and circuits you can build yourself.
Err. You DO change the speed by changing the voltage ! Using a linear regulator to drive a DC motor is perfectly satisfactory.

And PWM of a motor is actually different from modulating LEDs, because of the effect of the inductance of the motor on the actual current in the armature - it rises exponentially, but with good, low R parts nearly linearly with time, so the current waveform is sawtooth shaped. The effect of doing that, is that the mean voltage across the motor falls as duty cycle decreases.

jcaresheets (author)  kelseymh6 years ago
Ahhhh, as you can see I am used to AC power. OK good to know. Thank you I will look into it.
You say you are using AA batteries - that's DC.

. http://www.youtube.com/watch?v=acI12jO0HSQ
No, just can't read...