I am making my own motor but I want to know how many turns I should make it. I want it to be faster than the usual. I have small transformer so I used the coil in it, I don't actually know the diameter of the coil. Can anyone help I need to know how many turns are in the usual DC brushed motor. For your information, I know that all DC motors have different number of turns that's why I specified the motor in a DVD drive
The number of turns you need depends on the size of the motor, its design and construction (number of magnet poles, winding configuration etc.), what voltage it runs on, and how fast you want it go.
For any given motor of a particular construction, speed is inversely proportional to the number of turns (or alternatively, the number of turns required is directly proportional to the desired operating voltage). So if you halve the number of turns it will run twice as fast on the same voltage, or the same speed on half the voltage.
Working out how many turns are required from motor size and type alone is not practicable, but if you already have a motor then just unwind it and count the existing number of turns. If for some reason you can't do that then just try to get as many turns on as possible with the wire you have, and test it on a low voltage. Once you have determined the Kv (rpm/V) for that number of turns you can then calculate how many are needed to get the speed you want at the voltage you will be using.
DVD drives generally use a BLDC (Brushless DC) motor. These are good for rewinding because they have a stator in the center with arms that are easy to wind around. If you just want a bit more speed than you may not even have to rewind. They are usually wound in 'star' configuration. Simply separating the ends of each winding and rewiring in 'delta' configuration will make it ~73% faster.
Brushed motors are bit more difficult because the windings have to be attached to the commutator. Also the brushes are often quite delicate, making the motor a bit tricky to take apart and re-assemble. The primary advantage of a brushed motor is that you don't need a complex controller to run it.
Audio CD players often use a brushed motor to spin the disk because they don't need the superior speed and power of a BLDC motor. The Mabuchi RF-310TA-11400 is an example that does 2800rpm on 2.5V (or 5600rpm on 5V etc.). It has 400 turns of 0.11mm diameter wire on each arm of the armature.