Two most common types of stepper motor are bipolar and unipolar
look the diagram
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.
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…
Look what happens with the two phases (two coils) to understand the full step sequence
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.
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
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
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
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
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
or even instead mosfet, using ULN2003 for around 300mA current ,that is exactly that the upper video show ,using of course a 555 timer
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
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
But if we use half step angle we need 96 pulse for a recolution
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