What is a Stepper Motor?
To begin, we must understand what a stepper motor is and why they are necessary components of 3D printers. In a nutshell, a stepper motor is a kind of electric motor in which sequentially arranged electromagnetic coils are activated one by one in a specific order. This allows the motor to rotate in discrete steps.
While a conventional electric motor rotates for as long as power is supplied due to the fact that power is routed to all the coils, a stepper motor is able to achieve partial rotations. In other words, the sequential activation of the motor’s electromagnetic coils results in the motor shaft spinning a very precise number of degrees.
This feature of stepper motors makes them essential components of 3D printers. Moreover, due to the modular design of many 3D printers, there is a large range of motors that can potentially be installed on the device. For this reason, it is crucial to understand the important differences between different types of stepper motors and make sense of which parameters are important to consider when making a selection.
Types of Stepper Motor Drivers
The primary component of a stepper motor, and the one on which the specific performance parameters of the motor depend, is known as the stepper driver. The stepper driver is often referred to as the brain of the stepper motor.
Importantly, many prefabricated 3D printers already have drivers on either the mainboard or the sister board. Therefore, you do not necessarily have to change the driver when replacing the stepper motor on your 3D printer. The only thing to make sure of in this case is that the voltage used by the stepper motor is also within the voltage parameters of the driver.
Below are the three main types of stepper drivers to choose from, along with a brief overview of each one.
Bi-Level Stepper Driver
The bi-level stepper driver gets its name from the unique feature of being able to use a large range of voltages. The driver is designed such that when it uses a high-level voltage, it also draws a lot of current. This is necessary to improve the windings rise time of the motor.
Notably, once the bi-level stepper driver attains the appropriate level of current, it automatically switches off the high voltage supply. In this unique manner, the bi-level stepper driver is able to maintain the level of current that it requires from a low-level voltage.
The bi-level stepper driver’s unique capability of switching between low and high voltage supplies allows it to run very efficiently at a relatively low cost.
L/R Stepper Driver
The L/R stepper driver offers highly rated operation in an overall low-performing driver. Since it rotates at a relatively low speed, this stepper driver has a limited range of power outputs. Notably, the L/R stepper driver does not offer any variable control, meaning that the system only has moderate performance capabilities at best.
Chopper Stepper Driver (PWM) or the Microstep
The third and final kind of stepper motor driver is known as the PWM chopper stepper driver. PWM stands for pulse width modulation, and these drivers are also called micro-step drivers. The PWM Chopper makes use of an individually high-level supply of voltage, which sets it apart from the other stepper drivers mentioned above. Output transistors integrated into the design of PWM chopper drivers are set to automatically turn off and on, a feature that regulates the average level of current.
The Microstep or PWM Chopper Driver has the advantage of being able to run stepper motors while the driver is in Microstep mode. In the micro-step mode, the driver provides an amount of smoothness to the rotations that is greatly improved when compared with other drivers. Moreover, Microstep mode is able to guarantee excellent performance because it is able to regulate the rate of current across the full range of rotational speeds.
However, with all these complicated moving parts, the Microstep or PWM Chopper Stepper Driver is not very affordable to run and often becomes subject to overheating issues.
How to Choose Stepper Motor for 3D Printing
Now that we have covered the different types of stepper drivers, we can move on to how to choose the right stepper motor for your 3D printer. Choosing a stepper motor for 3D printing entails understanding the critical features of stepper motors and how these various features affect the performance and functionality of the 3D printer.
Below is an overview of several of these critical features, an understanding of which will help you choose the right stepper motor for your 3D printer.
Types of Current
Notably, stepper motors are able to operate using either Direct Current (D.C.) or Alternating Current (A.C.). Having said that, because stepper motors are most commonly used today for 3D printers, many stepper motors available today run exclusively on Direct Current because this is much better suited for the operation of 3D printers. This is simply due to the fact that all 3D printers require a D.C. supply for their heating components. However, in rarer cases, there are also stepper motors available that use Alternating Current to function.
Number of Windings
The electromagnetic array of a stepper motor makes use of windings, which are basically wires that are wound around a coil to produce an electromagnetic field within the motor, thereby enabling rotation. The number of windings in a stepper motor is an important feature to consider when choosing a stepper motor for 3D printing.
All stepper motors vary in the number of windings or wires they use. For example, bipolar stepper motors have an even number of wires from 4 to 8 and are optimally suited for bipolar drive. Meanwhile, stepper motors with, say, 5 windings cannot be run by a bipolar drive and can only be run in unipolar mode. Here, the pole in bipolar and unipolar refers to the magnetic poles (north and south) within the stepper motor that creates the magnetic field, which enables rotation.
There are two wires on the inside of four winding stepper motors, with the wire and coil pairs being dubbed as a phase. Conversely, stepper motors with 6 wires have two coils on the inside, with each coil having a center tap. The center tap allows for the creation of an additional wire for each coil by effectively cutting the coil in half. The decision to run the motor in full coil mode, whereby the center wires remain unconnected, or in half-coil mode, whereby two wires are left unconnected, is entirely up to the user.
Finally, a stepper motor with 8 windings makes use of four coils, resulting in two wires to one coil. The 8-wire stepper can also be run either in half or full-coil mode, a decision that is entirely up to the user. Lastly, when using the 8-wire stepper in full-coil mode, it is also up to you whether to connect the coils in a series circuit or a parallel one.
You can find stepper motors in a variety of different sizes. However, notably, the largest stepper motors are usually too powerful for a regular 3D printer. With this fact in mind, you should ideally go for a NEMA 17, which has a faceplate dimension of 1.7” by 1.7”. This particular size of stepper motor should be more than sufficient to guarantee enough power for the completion of any project that requires 3D printing.
If instead of substantial power, you would prefer a stepper motor with greater torque, you should go for the NEMA 23. Or, if you want a larger stepper motor with substantial torque, the NEMA 34 is an ideal choice. We will provide a more detailed outline of NEMA standards towards the end of this article.
The step count or stepping count of a stepper motor is what helps to achieve accuracy in both positioning and movement. Essentially, step count refers to the number of steps taken for each complete revolution, with the typical step count ranging from 4 steps to 400 steps. Moreover, 200 steps per revolution are equivalent to a rotation of 1.8 degrees for each step.
Notably, when trying to achieve greater resolution for your 3D printing project, you will have to sacrifice both torque and speed. In other words, a high step count shall lead to lower RPMs (revolutions per minute) relative to a similar-sized motor with a lower step count.
A higher step count allows the motor to rotate more efficiently and hence requires more power, which in turn lowers the torque. Therefore, in order to guarantee a high level of movement precision, the amount of generated torque needs to be low, and the step count needs to be high.
All stepper motors have a torque rating, which tells you how much power can be generated by the motor. Bigger motors are more powerful because they generate more torque. However, using a stepper motor with a high torque rating will mean that you will have to sacrifice movement precision.
When trying to decide what kind of stepper motor to choose for 3D printing, it is vital to make a note of your 3D printer’s size first. Typically, larger 3D printers require a motor with a greater torque rating in order to move the larger print head. Conversely, a smaller 3D printer will require a stepper motor with less torque
The NEMA Standard
The term NEMA is an abbreviation for ‘National Electrical Manufacturers Association’ and is a U.S based association that represents the interests of the United States’ electrical engineering industry. Essentially. NEMA is responsible for the nationwide standardization of electronic and electrical components. Furthermore, in cooperation with ISO, NEMA also sets worldwide standards for electrical and electronic components.
The NEMA standardization is used to assign and standardize the components of most stepper motors that are manufactured for 3D printing. Since advertised specifications and standards can always be counted on, this is extremely advantageous for the end-user. The description of the stepper motor may bear the abbreviation ‘NEMA,’ which is followed by a combination of letters and numbers that are used to specify the following features.
- The mounting plate
- The motor length
- The phases of current used
- The step count
- The torque rating
- The rotation speed
In the end, choosing the right stepper motor for 3D printing entails gaining a cursory understanding of the various features of stepper motors. Each of the features outlined above varies with different stepper motors, resulting in the ideal use case for each stepper motor being slightly different from the others.
By following the tips outlined in this overview and looking out for the specifications outlined by the NEMA standard for stepper motors, we are sure that you will be able to choose the best stepper motor for your specific 3D printing needs.