Stepper Motor

The use of stepper motors is one of the simplest, cheapest and easiest solutions for implementing precise positioning systems. These motors are very often used in various CNC machines and robots. Today I will talk about how the stepper motors are arranged and how they work.

What is a stepper motor?

First of all, the stepper motor is the motor. This means that it converts electrical energy into mechanical energy. The main difference between it and all other types of engines is the way in which rotation occurs. Unlike other motors, stepper motors rotate NOT continuously! Instead, they rotate in steps (hence their name). Each step represents a part of the full turnover. This part depends, in the main, on the mechanical arrangement of the motor and on the chosen method of controlling it. Stepper motors also differ in their feeding methods. Unlike AC or DC motors, they are usually driven by pulses. Each pulse is converted to the degree to which the rotation occurs. For example, a 1.8º stepper motor rotates its shaft by 1.8 ° with each incoming impulse. Often,

Basics of the stepper motor

Like all motors, stepper motors consist of a stator and a rotor . The rotor has permanent magnets, and the stator includes coils (windings). Stepper motor, in general, looks like this:

Here we see 4 windings, located at an angle of 90 ° in relation to each other, placed on the stator. Differences in the ways of connecting the windings ultimately determine the type of connection of the stepper motor. In the figure above, the windings are not connected together. The motor in this circuit has a pivoting step equal to 90 °. Windings are used in a circle - one after another. The direction of rotation of the shaft is determined by the order in which the windings are activated. Below is the work of such an engine. The current flows through the windings at intervals of 1 second. The motor shaft rotates 90 ° each time a current flows through the coil.

Control Modes

Now let's look at the various ways of supplying current to the windings and see how the motor shaft rotates as a result.
Wave control or full-step control of one winding

This method is described above and is called wave control of one winding. This means that only one winding carries an electric current. This method is rarely used. Basically, it is used to reduce energy consumption. This method allows you to get less than half the torque of the motor, therefore, the load of the motor can not be significant.


Such an engine will have 4 steps per revolution, which is the nominal number of steps.

Full-step control mode

The second, and most commonly used method, is a full-step method. To implement this method, the voltage to the windings is supplied in pairs. Depending on the way the windings are connected (in series or in parallel), the motor will require a double voltage or a double current to operate with respect to the required winding of one winding. In this case, the motor will produce 100% of the rated torque.

Such a motor has 4 steps per full revolution, which is the nominal number of steps for it.

Half-step mode

This is a very interesting way to get double the accuracy of the positioning system, without changing anything in the hardware! To implement this method, all pairs of windings can be fed simultaneously, as a result of which, the rotor will turn to half its normal pitch. This method can also be implemented using one or two windings. Here's how it works.

Single winding

Two-winding mode

Using this method, the same motor can give twice the number of steps per revolution, which means double precision for the positioning system. For example, this motor will give 8 steps per revolution!

Microstep mode

Microstepping is the most commonly used method for controlling stepper motors to date. The idea of ​​the microstep is to feed the motor windings of the power supply not with impulses, but a signal, in its form resembling a sinusoid. This method of changing the position from one step to the next allows a smoother movement, making stepper motors widely used in applications such as positioning systems in CNC machines. In addition, the jerks of various parts connected to the motor, as well as the tremors of the motor itself, are significantly reduced. In microstep mode, the stepper motor can also rotate smoothly as conventional DC motors .


The shape of the current flowing through the winding is similar to a sinusoid. Forms of digital signals can also be used. Here are some examples:

The microstep method is in fact a method of supplying the motor, and not a method for controlling windings. Therefore, microsteps can be used for both wave control and full-step control mode. The work of this method is shown below:

Although it seems that in the microstepping mode, the steps become larger, but, in fact, this does not happen. To improve accuracy, trapezoidal gears are often used. This method is used to ensure a smooth movement.

Types of stepping motors

Stepper motor with permanent magnet

The rotor of such a motor carries a permanent magnet in the form of a disk with two or more poles. Works exactly as described above. The stator windings will attract or repel the permanent magnet on the rotor and thereby create a torque. Below is a diagram of a stepper motor with a permanent magnet.

Usually, the step size of such engines lies in the range of 45-90 °.

Stepper motor with variable magnetic resistance

For engines of this type, there is no permanent magnet on the rotor. Instead, the rotor is made of magnetically soft metal in the form of a gear, such as a gear. The stator has more than four windings. Windings are powered in opposite pairs and attract the rotor. The absence of a permanent magnet negatively affects the amount of torque, it significantly decreases. But there is a big plus. These engines do not have a stopping torque. The stopping torque is the torque generated by the permanent magnets of the rotor, which are attracted to the stator reinforcement in the absence of current in the windings. You can easily understand what it is for a moment if you try to turn the hand off the stepper motor with a permanent magnet. You will feel distinguishable clicks at each step of the engine. In fact, what you will feel and will be a fixing moment, which attracts magnets to the stator reinforcement. The work of a stepper motor with variable magnetic resistance is shown below.

Stepping motors with variable magnetic resistance usually have a step lying in the range of 5-15 °.

Hybrid Stepper Motor

This type of stepper motors was named "hybrid" because it combines the characteristics of stepper motors with permanent magnets and with variable magnetic resistance. They have excellent holding and dynamic torque, as well as a very small step size, lying within 0.9-5 °, providing excellent accuracy. Their mechanical parts can rotate at higher speeds than other types of stepper motors. This type of engine is used in high-end CNC machine tools and in robots. Their main disadvantage is high cost.


A conventional motor with 200 steps per revolution will have 50 positive and 50 negative poles with 8 windings (4 pairs). Due to the fact that such a magnet can not be produced, an elegant solution has been found. Two separate 50-tooth discs are taken. A cylindrical permanent magnet is also used. The disks are welded one with the positive, the other to the negative pole of the permanent magnet. Thus, one disc has a positive pole on its teeth, the other - a negative one.

Two 50-tooth discs are placed on top and bottom of a permanent magnet

The trick is that the disks are placed in such a way that if you look at them from above, they look like one 100-tooth disc! Elevations on one disk are combined with depressions on the other.

The depressions on one disk are aligned with the elevations on the other

The following is the work of a hybrid stepper motor, having 75 steps per revolution (1.5 ° per step). It is worth noting that 6 windings are paired, each has a winding from the opposite side. You probably expected the coils to be at an angle of 60 ° after each other, but, in fact, it's not. Assuming that the first pair is the uppermost and lowest coils, then the second pair is shifted at an angle of 60 + 5 ° with respect to the first, and the third is shifted by 60 + 5 ° relative to the second. The angular difference is the reason for the rotation of the motor. Control modes with full and half step can be used, however, as well as wave control to reduce power consumption. Below is shown the full-step control. In the semi-step mode, the number of steps will increase to 150!




Do not try to follow the windings to observe how this works. Just focus on one winding and wait. You will notice that whenever the winding is engaged, there are 3 positive poles (red) at 5 ° behind which are attracted in the direction of rotation and the other 3 negative poles (blue) at 5 ° in front, which are pushed in the direction of rotation. The active winding is always between the positive and negative poles.

Connection of windings

Stepper motors belong to multiphase motors. More windings, then more phases. More phases, smoother operation of the motor and more expensive cost. The torque is not related to the number of phases. The most common are two-phase motors. This is the minimum amount necessary for a stepper motor to function. Here it is necessary to understand that the number of phases does not necessarily determine the number of windings. For example, if each phase has 2 pairs of windings and the motor is two-phase, the number of windings will be 8. This determines only the mechanical characteristics of the motor. For simplicity, I will consider the simplest two-phase motor with one pair of windings per phase.


There are three different types of connection for two-phase stepper motors. The windings are interconnected, and, depending on the connection, a different number of wires are used to connect the motor to the controller.

Bipolar motor

This is the simplest configuration. Use 4 wires to connect the motor to the controller. Windings are connected internally in series or in parallel. Example of a bipolar motor:


The motor has 4 terminals. Two yellow terminals (colors do not correspond to the standard ones!) Feed the vertical winding, the two pink ones - the horizontal winding. The problem with this configuration is that if someone wants to change the magnetic polarity, the only way is to change the direction of the electric current. This means that the driver circuit will become more complicated, for example, it will be an H-bridge.

Unipolar motor

In a unipolar motor, the common wire is connected to the point where the two windings are connected together:


Using this common wire, you can easily change the magnetic poles. Suppose, for example, that we connected a common wire to the ground. Having fed one output of the winding first, and then the other - we change the magnetic poles. This means that the circuit for using a bipolar motor is very simple, usually consists of only two transistors per phase. The main drawback is that every time, only half of the available coil windings are used. This is the same as in the wave control of the motor with the excitation of one winding. Thus, the torque is always about half the torque that could be obtained if both coils were engaged. In other words, unipolar motors should be twice as large as the bipolar motor in order to provide the same torque. A unipolar motor can be used as a bipolar motor. To do this, leave the common wire unconnected.


Unipolar motors can have 5 or 6 pins for connection. The figure above shows a unipolar motor with 6 leads. There are engines in which two common wires are connected internally. In this case, the motor has 5 terminals for connection.

8-pin stepper motor

This is the most flexible stepping motor in terms of connection. All windings have conclusions from both sides:


This engine can be connected in any of the possible ways. It can be connected as:

• 5 or 6-pin unipolar,
• bipolar with series-connected windings,
• bipolar with parallel-connected windings,
• bipolar with one phase connection for applications with low current consumption