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Stepper motors are DC motors that move with different steps. They have multiple coils organized in groups called "phase". By energizing each phase in turn, the motor will rotate one step at a time. You can do very precise positioning and/or speed control with step control with computer. Stepper motors are preferred for very precise motion control applications. Stepper motors come in many different sizes and styles and electrical specifications. It is important that you use the right stepper motor for the job.
Usage Areas of Stepper Motors
Positioning: Because Stepper Motors move in precise repeatable steps, they are perfect in applications that require precise positioning such as 3D printers, CNC, Camera platforms and X, Y Plotters. Some disk drives also use stepper motors to position the read/write head.
Speed Control: Precise motion increments also provide excellent control of rotational speed for process automation and robotics.
Low Speed Torque: Normal DC motors do not have much torque at low speeds. The stepper motor has maximum torque at low speeds, so it is a good choice for applications that require low speed with high precision.
Stepper Motor Types
There are a wide variety of stepper motor types, some of which require very specific drivers. Commonly used stepper motors; Permanent Magnet or Hybrid Stepper Motors are 2-phase bipolar stepper motors and 4-phase unipolar stepper motors. One of the first things to consider is the work the engine has to do. Bigger engines can provide more power. Stepper motors can be smaller than a peanut or very large like the NEMA 57.
To decide if the engine has the power to do what you want, you need to look at the torque rating. NEMA 17 Stepper Motors are a common gauge used in 3D printers and small CNC projects. Smaller motors are used in many robotic and animatronic applications. Larger NEMA sizes of motors are common in CNC machines and industrial applications. NEMA numbers define standard shield plate sizes for mounting the motor. They do not define other characteristics of an engine. Two different NEMA 17 motors can have completely different electrical or mechanical properties.
Number of Steps
The next point to consider is the positioning resolution you want. The number of steps per revolution is between 4 and 400. Commonly available steps are 24, 48, and 200. Resolution is often expressed in degrees per step. A 1.8 degree motor is the same as a 200 step/revolution motor.
Unipolar vs Bipolar
Unipolar drivers always energize the phases in the same way. One Lead, the "common" lead, will always be negative. The other end will always be positive. Unipolar drivers can be implemented with a simple transistor circuit. The downside is that there is less available torque because only half of the coils can be energized at a time.
Bipolar drivers use the H-bridge circuit to actually reverse the current flow in the phases. By energizing the phases by changing the polarity, all the coils can start trying to turn the motor.
A two phase bipolar motor has 2 groups of coils. A 4-phase unipolar motor has 4. A 2-phase bipolar motor has 4 wires, 2 for each phase. Some motors come with flexible cables that allow you to run the motor bipolar or unipolar.
5 Wire Stepper Motor
Common in small unipolar motors. All of the common coil wires are connected to the pull-out wire as the 5th wire. This motor can only be driven as a unipolar motor.
6 Wire Stepper Motor
Combines the common wires of 2 paired phases. These two wires can be combined to form a 5-wire unipolar motor.
You can ignore it and pretend to be a bipolar motor!
8 Wire Stepper Motor
The 8-wire unipolar is the most versatile motor of them all. It can be run in several ways:
4 phase unipolar - All common wires are connected together - just like a 5 wire motor.
2-phase series bipolar - Phases are connected in series - like a 6 wire motor.
2-phase parallel bipolar - Phases are connected in parallel. This results in half the resistance and inductance - but requires twice the current of the driver. The advantage of this wiring is higher torque and top speed.
Finding Stepper Motor Tips
The best solution is to obtain the pinout from the engine manufacturer. If you do not have the opportunity to find the wiring diagram, the following procedure will help you yourself.
4-Wire Stepper Motor
When you measure with a multimeter, both phases must have the same resistance. When you measure the resistance in the cables using the Ohm step, whichever 2 wires you get resistance value, those 2 wires are the ends of the same coil. When we call one of these terminals A1 and the other A2, the remaining 2 wires become B1 and B2. We'll find the motor wires. If the motor rotates in the opposite direction, reverse either A1 and A2 or B1 and B2.
6 Wire Stepper Motor
After taking the multimeter to the ohm range, when we connect one wire to one end of the multimeter and measure the resistance value with the other wires, we get the resistance value from the 2 wires. In 6-wire stepper motors, each phase has a center end. The 3 wires we found resistance value are the ends of the same coil. The resistance value of the center end and the other ends is half the resistance value between A1 and A2. You can measure with a multimeter and find the leads. You can make the same measurements on the other three cables and find the B1 and B2 ends. If the motor rotates in the opposite direction, reverse either A1 and A2 or B1 and B2.
How to Drive Stepper Motor?
Driving a stepper motor is a bit more complicated than driving a DC motor. Stepper motors require a step controller to energize the phases to make the motor rotate. Let's examine the use of stepper motor with Arduino with A4988 Stepper Motor Driver and TB6600 Stepper Motor Driver.