Bipolar and unipolar motors

Two most common types of stepper motor are bipolar and unipolar

 

look the diagram

 

motor_coil_configurations

 

 

As a general rule of unipolar and bipolar motors

  • 4 Wires: Bipolar only
  • 5 Wires: Unipolar only
  • 6 Wires: Universal
  • 8 Wires: Universal

Thing are simple. Unipolar and bipolar is the type of connection each motor.The only difference is that bipolar can not be connected as unipolar (because it has only 4 wires) ,but unipolar can be connected ae bipolar.

Bipolar stepper motors

Bipolar motors have a single winding per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole, so the driving circuit must be more complicated, typically with an H-bridge arrangement (however there are several off the shelf driver chips available to make this a simple affair). There are two leads per phase, none are common.

Because windings are better utilized, they are more powerful than a unipolar motor of the same weight. This is due to the physical space occupied by the windings.

 

Full step

Next photo show full step of bipolar motor. If we take the order 1,3,5,7 the motor turn right and if we take the order 7,5,3,1 motor turn left. if we are at the first state and we want to go to the next step ,for example to turn step angle 7.5 step degree, we have to the reverse the  polarity of the first phase  (I1)and so on…

 

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Look what happens with the two phases (two coils) to understand the full step sequence

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Half step

The next photo shows what is exactly half step on bipolar motor.The first state is exactly what is the first state  at full step sequence.

But second state we can see the current to one of two  phases is 0 (I1).At state 4 the second phase is 0 and so on…That double the number of angles ,if for example motor is 7.5 step/angle ,with half step we have 3.75step. Smoother rotation and more precised move butt remember, we have proportion reduction.

 

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Take care what happens here. It is easy to understand here, that for a few milliseconds of a revolution ,on each one phase(coil) we have 0 current.That is why we have torque reduction but we also have torque reduction when speed of motor is increasing

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Unipolar stepper motors

A unipolar stepper motor has two windings per phase and of course two phases, one winding for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching the direction of current, the commutation circuit can be made very simple (eg. a single transistor) for each winding.

The diagram of our motor is here

howsteppermotorswork_1273304680

Unipolar motor has 5,6 or 8 wire. If it is 5, both midle pins of two phases are connected. If it has 6 wire, middle pins of phases are not connected

 

 

 

 

 

Full step

what exactly is full step you can to the next video

 

Aw you can understand we give one pulse each time to each wire.. We cut of the pulse and we give a pulse to the next wire.

The must be a right sequence of wire to turn motor properly on onw  side. If we find that sequence and give pulses to the opposite side, motor will turn the opposite side

howsteppermotorswork_1273227605

Exactly this is happening on full way step

 

 

 

 

 

 

As about circuit, you can make for full step modding ,if motor current is some amps, using   IC 14017 Decade Counter and  4 mosfet

simpleunipolarsteppermotorfullstepcontroller_1279216479

 

or even instead mosfet, using ULN2003 for around 300mA current ,that is exactly that the upper video show ,using of course a 555 timer

 

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Half step

A good video explaining with buttons is here. That motor is 7.5 angle. Because of half step , each pulse it will rotate 3.75 degree

With this way we ca to achieve double the accuracy of a positioning system, without changing anything from the hardware! According to this method, all coil pairs can be energized simultaneously, causing the rotor to rotate half the way as a normal step. This method can be single-coil or two-coil excitation as well

 

howsteppermotorswork_1273229649

howsteppermotorswork_1273229444

 

 

 

 

 

 

 

one coil charge                                                                                                                           two coil charge

 

 

 

 

As a conclusion we can say that having two motor with the same frame size, using the motor as bipolar connection we have 40% more torque power.That is because bipolar has a better use of the coils. Thos motor are use for high performance applications

But unipolar motor has an aesier drive circuit and are used for low performance applications, such a feed printer paper  scanners and much more

A common motor 7.5 step angle need 48 pulse using as full step to make a revolution

7.5*50=360

But if we use half step angle we need 96 pulse for a recolution

3.75*96=360

We can see that we have more steps angle so the motor moves much more smoother but we have to take into mind that torque power is proportion reducing

 

Another motor have with 1.8 step angle need 200 full step pulse for a revolution

 

If we charge the coils proportion , we can achieve 1/4,1/8,1/16 and even 1/32 microstepping but loosing power and sometimes and loosing and steps,very bad in some situations.

There is a very nice program that you can use with your parallel port of your computer along with a few componets ,so that drive any bipolar or unopolat motor

Click here to download

 

 

 

 

2 thoughts on “Bipolar and unipolar motors”

  1. I am now not certain where you’re getting your info, however great topic.
    I needs to spend some time learning more or understanding
    more. Thanks for wonderful info I used to be in search of this info for my mission.

    1. Hi friend thank you, all infos are from internet.
      The main secret here is to search in internet and separate just what you need to know, don’t loose yourself with all those huge info , keep only what you need!
      In this topic is what i need for bipolar an unipolar motor, nothing more.
      Happy learning..

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