[fraist]

Hi,I'm a newbie in electronics.So ,I want to know the difference between a servo, a stepper and a DC motor.If possible, can you give me a special characteristic that differs one another. Thanks for your time!

[Al_The_Man]

Do a search here there is quite a few posts already giving you in depth explanations.
Al.

[alrassoul]

well, you have to know that stepper motors or step motors come in two types :
unipolar and bipolar motors.
the unipolar motors comme with 4,5,6 and even with 8 wires , while the bipolar ones come solely with 4 wires.
There are many integrated circuits ICs dedicated to drive them, among them the couple L397/L398, or ULN3904, or the A39XX where XX stands for many numbering types from which we can find some speciallized in driving servo motors.
the step motor is a motor that can move only in steps, that is every time we energize its 2 coils, it moves one tooth that is one step.
The step may be in fact either a full step, or a half step, or even microstep.
By microstep, we intend the possibilioty to drive a step motor by sinusoidal like driving current, that has the for of a stair case like shape.
each step whoul drive the motor a fraction of a full step, which goes from 2, 4,8,16 or even which is in my opinion the maximul now a day acceptable 256 microsteps.

That's for a brief insight into the marvellous worls of step motors.

For the servo motor, it is maily a Dc or AC motor, they come in brushed or brushless type, but with the addition of a feedback to the controlling device to let him know the shaft position , its speed and even its acceleration.

This is achieved through a quadrature encoder, which comme in different types, Agilent Ltd provide many types which are very versatile as well as other manufacturers.

These quadrature data is mainly of 2 forms ENCA, ENCB, which are mainly 2 square waves in qhadratures, that is 90° out of phase, and the INDEX signal which is a pulse set to the controller every turn.

Somme times, weget differential quadrature signals, that is ENCA and ENCA/,ENCB and ENCB/, as well as of course the INDEX signal.

ENC/ and ENCB are the differential signals whith respect to ENCA and ENCB respectively, that is when ENCA goes HIGH, ENCA/ goes LOW and vice versa, the same thing goes for ENCB and ENCB/.

The SERVO MOTOR is no more than a DC motor controlled in such a way, to provide total control by means of a resolver or in our case a qauadrature encoder to control its position and speed.

Cheers.

[fraist]

I see.....
thanks for the reply alrassoul.I'm starting to understand now.....