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Mat's Electronics corner, a good place to learn and have fun!!!
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STEPPER MOTORS

An easy way to automation is to work with stepper motors. There is no tune up, no encoder, no feedback, just a step and direction signal that can easily be generated from a parallel port from the computer. Well that sounds very easy!!!

Now lets take a look inside a stepper motor.
As you see nothing different from a regular dc motor except from the fact that in the stepper motor there are more wires that in the regular two cables dc motor(well its a lot more different, but i like to joke around!!:P ).

On a dc motor there are windings in the rotor(the part that rotates) and the magnets are on the stator(the outer part).
In a dc motor there are brushes fixed in the stator that connect to the rotor to to transfer the energy to windings and as the rotor moves it also accomplish the function of switching the different windings.

On a stepper motor things are different the stator has in general 2 windings as you see in the picture and in the rotor there is a magnet also show in the pics. If you look at the detailed picture you will notice some dents, well these dents are the key to the stepper motor to function.
How does this works???
When you energize one of the windings it will generate a magnetic north and a magnetic south. This will force two dents on the rotor to align with a pair in the stator(one in the north pole and another one in the south).
As you see not all the dents align, only two pairs will be aligned each pair on a pole. Leaving the rest of the dents with different alignments. There will be two pair of the dents that are gone be the most close to be aligned and depending on how you energize the other winding(positive negative or negative) the motor will rotate in one direction or the other forcing one of these two pairs of dents to align. And again you will have a pair of dents aligned and 2 possible pairs for alignment. And you will be able to rotate the motor one step to one side or the other.
What i just described is called a full step and its the product of sequence of one winding always energized. There is another possibility of sequences of 2 windings energized and 1 winding energized that is called "half step" and it will double the resolution of the stepper motor.

Now lets take a look at a simple circuit to drive a stepper motor PAGE2