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Wszystko o silnikach krokowych

What is stepper motor?

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Stepper motors are DC motors that move with the help of special jumps. They have numerous coils, assembled in a group called "phases". Supporting each of them, it begins to rotate.

You can get very precise positioning and/or adjusting the speed and controlling it via the computer. Because of this, they are chosen for many applications, controlling the movement accuracy.

Stepper motors have different sizes and styles, as well as electrical parameters. This tutorial will tell you everything you need to know when choosing a suitable engine.

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A 4-phase unipolar motor

Animation from Wikipedia

Where can you use stepper motors?

  • The positioning of these Engines move through specific, repetitive jumping, so the best will be in applications that require precise positioning, for example, 3D printer, CNC machine, platforms for cameras and Plotters, X-y Some discs also use stepper motors for head positioning solenoid.
  • Speed adjustment - the Exact increase in traffic allows perfect control of rotational motion in the process of automation and robotics.
  • Low torque Standard DC motors have high torque at low speed. And, the stepper motor has maximum torque at low speed. So it is a good choice if you are looking for the above mentioned engine speed and high precision.

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What are the limitations?

  • Poor performance - Load current of a stepping motor irrespective of load. They consume more electricity when not working. Because of this, usually to heat.
  • Limited high-torque - stepper Motors have lower torque, but not at low but also at high speeds. Some of them are optimized to have higher speeds. To achieve them, they must be paired with an appropriate controller.
  • The lack of feedback - most of the stepper motors does not have integral feedback when positioning. Although high accuracy can be achieved by the inclusion in the "open loop". Limit switches or sensors animals are usually necessary to protect and/or to determine the position of the links.

Types of stepper motors

There is a wide range of stepper motors, some require very specialized drivers. In our article, we will focus only on those that can work with widely available drivers. This is: a permanent magnet motor or hybrid engine, a two-phase bipolar or czterofazowy unipolarny.

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The size of the engine

One of the first things that you should consider is the work the engine must perform. You can find that the larger ones can deliver more power. Stepper motors can be the size of a walnut, but as large as 57, and NEMA.

Most of them has a nominal value of torque. For this you have to be careful when deciding that the engine has enough power.

NEMA 17 motor with a typical size used in printers, 3D in small milling machines with CNC. Small engines are used in many robotic and animatronicznych projects. Large NEMA motors are typically used in CNC machines find application in the industry.

Determine the number of NEMA standard dimensions end plate when installing the motor. They do not determine the other parameters. Two different NEMA 17 motors have completely different electrical and mechanical characteristics. They are not interchangeable.

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Step counter

Following that drew the attention required positioning resolution. The number of steps per revolution has a range of 4 to 400. Widely available counts steps, 24, 48 and 200.

Resolution is often expressed in degrees per step. The motor is 1.8°, the same as the engine 200 steps per revolution.

Compromise high-resolution speed and torque. Engines with a large number of steps, work better at lower rpm. Faster speed also reduces the torque.

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Mechanical box

Another way for a high positioning resolution is the use of a gearbox. Effect of application of the reducer 32:1 at the output of the motor 8 steps per revolution, the engine will be 512-step.

Mechanical box it will also increase the engine torque. Some small stepper motors with gear have amazing torque. But the tradeoff of course is speed. Stepper motors with gear used, typically used in projects at lower rpm.

Style shaft

The next question worthy of Your attention, is the engine with the rest of the powertrain. The available engines with the shafts in different styles:

  • Shaft "D" or round: they are available in various standard diameters. A lot of pulleys and sprockets, and shaft connectors are designed in such a way that they were matched. The flat side walls "D" prevents slippage. They specified when high torque.
  • Drive belt: Some shafts have wyfrezowane teeth of the gear. They are, as a rule, is designed to cooperated with a miniature gearboxes.
  • Screw shaft: the screw shaft Engines are used for the construction of linear actuators. Their miniature version is a series of heads in disk drives.

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Posting

There are many types of cables to stepper motors. We will focus on those that can be moved widely available drivers. It's a permanent magnet motor or hybrid, connected as 2-phase bipolar or as 4-phase unipolarny.

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Coil and phase

The stepper motor may have any number of coils. However, they are United in groups called "phases". All coils in a phase are fed together.

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Driver unipolarny vs bipolar

Driver unipolarny always feeds the phase in the same way. One "common" wire will always be with a negative charge. Second, be positive. These drivers can be implemented with simple transistor circuits. Its disadvantage is that it has less torque because only half of the coils can be powered at the same time.

The bipolar driver uses the layout of the H bridge to be able to reverse the flow of current through the phases. And transmits them naprzemienną polarity, all the coils start to work, simultaneously starting the engine.

A two-phase bipolar motor with 2 groups of coils. Engine 4-phase unipolarny no such groups 4. 2-phase bipolar will have 4 wires - 2 for each phase. Some engines have flexible cables that allows the engine start in mode unipolarnym or bipolarnym.

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Engine 5-wire

All common wire coil, connected in the center and displayed as a 5 cable. This engine can operate only in the unipolarnym.

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Engine 6-wire

It combines only the common wires of 2 paired phases. Wires can be connected to create a 5-wire unipolarny engine.

You can also use the motor as a bipolar, not paying attention to the wires.

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8-wire motor

This unipolarny engine is the most versatile of all. Can be controlled in various ways:

  • 4-phase unipolarnie - all the common wires are connected the same way as in the case of an engine 5-wire.
  • 2-phase bipolarnie commercially - phase are connected in series in the same way as in the case of motor 6-wire
  • 2-phase parallel bipolarnie - phase are connected in parallel. This leads to twice lower resistance and inductance - however, requires twice the current to run. The advantage of such a transaction is a higher torque and maximum speed.

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The use of stepper motor

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A stepper motor is a bit more complicated to use than the standard engine szczotkowy on the DC. Stepper motors need to have your driver to be able to expand the phases in the correct order which thus napędzą engine.

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Easy driver unipolarny

The simplest type of controller can be constructed using a small number of transistors. They are turned on and off in sequence, to replenish the land and start the engine. The construction of these drivers is relatively cheap, but they work only with engines unipolarnymi. Tutorial to do this driver you will find on the Arduino web site.

[link 1] Tutorial stepper driver unipolarnego

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A simple two-channel driver connected to the output H

The use of a bipolar motor requires 2 axles H, so that the current could go back in phases. But to build them from scratch can be difficult. Available designs mostkowych H, which can make it easier.

L293D is one of the most popular and economical systems. It can be found in the basics of most engines disk of the first generation.

Learning with Arduino, you will find a great tutorial on how to use the L293D with the Arduino:

[link 2] Lesson 16 - stepper Motors

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A hydraulic motor V2 Adafruit

A hydraulic motor V2 Adafruit is a great progress in relation to key drivers on the basis of the L239D. Shell V2 uses two TB6612 MOSFET driver. Compared to L293D TB6612 offers twice the performance of current and significantly lower voltage drop, which simplifies the use of this engine.

The 2 controls and 4 mostkom H, each mask can power up to two motors. Of the control system are connected through system control PWM with I2C interface. Frees up a lot of GPIO pins that you can use on something else, and frames can be stacked on top of one another. You can be up to 32 covers, which will control up to 64 motors using 2 IO pins.

All information about this driver, see in the education System.

[link 3] Guide for grid engine V2 Adafruit

Optional CNC controllers

Tile control CNC gShield and TinyG will bring You closer to the performance of the stepper motor at the industrial level. They are constant current drivers, called "helicopter". They can be adjusted to provide maximum torque and the engine speed.

TinyG CNC is installed on the Board to interpret G-code and 4 output of the engine. Because of this, small and medium-sized 4-axis CNC machines have a full turnkey solution.

Although these extra-plate high performance are more complicated and recommended for more experienced users.

Information about these plates and their operation can be found on the TinyG Wiki and on the Synthetos forums.

[link 4] - the Synthetos Forums

[link 5] Tiny G Wiki

Configure stepper motor driver

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Go to the most important part: make sure that the motor and driver are compatible with each other.

The result of their bad choices may be unsatisfactory performance, and, worse, engine damage and/or controller.

If improperly selected, can You meet it:

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We invite you to see driver settings

Two main parameters of the driver:

  • Voltage - maximum voltage that can be delivered to the engine
  • Continuous current - the maximum continuous current that can be delivered to the engine

Values sczytowe the current does not have applications in stepper motors. Always use the rated continuous current

Check the engine parameters

You also need to know the parameters of the engine. There are 2 important parameters:

  • How many per phase is the maximum current with which the motor windings can handle without overheating
  • The resistance per phase is the electrical resistance per each phase

Voltage nominal, as a rule, this. Calculates them using the two options above - but not always. It is better to calculate them myself, also with the help of above ratios, but in the Ohm's Law.

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Follow the law!

Phase stepper motor are inductive coils, which are not subject to sudden changes in current flow. But at the end of each turn, or in the absence of motion, acting like a resistive load and in accordance with Ohm's Law.

The motor consumes more current when it does not work. Ohm's law allows the use of engine parameters to calculate the current needed by the controller.

Voltage = Current x Resistance

or

Current = Voltage / Resistance

These models should be closely used in all drivers stepping motors DC. This also applies to motor protection V1 and V2 from Adafruit, and almost all other controllers on the basis of the L293D.

However, some engines have a very low rezystencję coil. Therefore, the use of these models leads to the fact that the voltage is lower than 5V, and the performance will not be satisfactory. This type of motor is not suitable for the driver with constant voltage and requires a more specialized controller.

You want to break the law?

If we are talking about Ohm's Law, then no one haven't made it yet. Don't even try, because it will end badly. Although, there are other laws. Law of Lenz, Faraday and Ohm will help You to increase the performance of Your engine.

Coil of the stepper motor produce a magnetic field when they are working. According to the Faraday's Law, changing magnetic field causes a current flow in the coil. And according to Lenz Law, this current will pass in the opposite direction to the current, creating a magnetic field. This reverse current is known as "retroactivity elektromotoryczna" or reversing EMF.

This force increases the "resistance" or uskutecznia coil resistance. So the Law of Ohm is still valid, but only resistance, not a simple resistance area. Nand at the beginning of each turn,the resistance limits the current through the coil.

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Drives Chopper

The drive of the Chopper, or on DC balances the reversing electromagnetic field filling the engine with higher voltage. Drive stepper motors is several times higher voltage than the nominal through the shredder drive is normal.

At such high voltages, need to take care of security. For this purpose, chopper drive, it also monitors the current supplied to the motor, and "remove" it from exceeding the originally established level.

Since higher voltages, our driver is able to deliver more current to the coils in the beginning of the turn, while increasing available torque. In addition, it allows large maximum speed.

You have to understand the operation of the motor and controller if you want to find a chopper driver and install it with a specific engine.

FAQ

If this engine will work with my defense?

You need to check the parameters of the motor and controller. Then go to the "configure stepper motor driver" and see if they match.

NEMA 17 should work... right?

Size NEMA only defines the size of the artboard. In order to know if it works, you need to know the electrical parameters of the motor.

What size engine I should choose for my project?

Most motors have torque settings - usually in inch / ounces or niutonach / cm. One inch / ounce, this means that the engine can exert a force of one ounce at one inch from the center of the shaft. For example, it can withstand one ounce force using a pulley with a diameter of 2 inches.

When calculating the torque, make sure that you include there was an additional, which is required for acceleration and to overcome abrasion. Something to cheer you more torque, than to keep it.

If Your project requires a large amount of chances, but at low speed, check the stepper motor with reducer.

How to connect the motor to the lid?

Wiring instructions written in the product description, if you have the Adafruit motor.

In the case of other engines, check the specifications of the engine, if Yes, the one you have.

Is there any power supply will work with my engine?

First, make sure that you do not exceed the voltage rating assigned to the engine controller.* To run it at low voltage, but it can then have a smaller torque.

* This only applies to drivers with direct current.

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