How to controlling speed on a motor?
Find a space on your breadboard to place your potentiometer. The central pin of the potentiometer is connected back to pin 9 using a jump wire, and the remaining two pins are connected to 5V on one side and GND on the other.
Stepper? Continuous rotation? DC? AC? BLDC? Servo? All of these are appropriate for different purposes, and use different schemes to control the speed. If you are unsure what the right kind of motor for your project is, you can tell us what you're trying to do, and get some thoughts on what the right motor is.
ericapolidu:
Find a space on your breadboard to place your potentiometer. The central pin of the potentiometer is connected back to pin 9 using a jump wire, and the remaining two pins are connected to 5V on one side and GND on the other.
Wrong thread?
Speed control methods of the various speed control motors
The output control method of a speed control circuit can be divided roughly into two groups: phase control and inverter control.
AC speed control motor & gear motors
Brushless DC motor unit
Inverter unit
Okay, you have some kind of DC motor, and you want to control the speed with a potentiometer, presumably connected to an Arduino.
So What kind of motor driver are you using now?
We don't like vagueness here, because then we end up solving a problem that isn't the same as the problem you have (wasting our time writing it and your time reading our posts), and giving bad advice because we don't realize what you're trying to do.
Hi,
Can you post a link to specifications/data on your motor?
Can you post a picture of your motor please?
We need to know what size your motor is so we can give you the correct information.
What model arduino controller are you using.
Thanks.. Tom... 
PS What is your native language?
We also need to know what you are using as a motor driver - you need something to switch the motor on and off, since a single Arduino pin can't supply enough current to drive even a very small motor.
Do you have a picture of your setup?
Read the potentiometer with analogRead(). Divide by four and send the result to an output pin with analogWrite(). You need a transistor or driver to supply the power to the motor, the Arduino pin doesn't have enough. This has been done about a million times.
... and yes, language barrier is no excuse for not giving details on the motor. You can use photos, links, or diagrams.
is just a regular motor, the DC motor, and control by poteniometer
Turn the potentiometer shaft to reduce the speed.
He PMed me with a bit of info not here - it's the motor that came with one of the starter kits, one of those little motors.
So I think he is just using a motor and transistor to drive it.
So connect potentiometer like ericapolido said above (reply #2). Code like aarg said in reply #14
@acewu, would you happen to be a student at Queen Margarets School?
@ericapolidu, would you happen to be a student at Queen Margarets School?
acewu:
@Coding Badly, would you happen to be a student at Queen Margaret's School?
Lame.