Blog - Sketching with Hardware

Stepper Motors

Published on: | Author: Sakina Mammadova | Categories: 2018b, Tutorials

In this blog post I will talk about stepper motors. 

First I am going to give you some information you need to know about these motors. Afterwards I will explain why we used stepper motors in our project (see blog post about Snack2Go). 

Are you ready? Let’s go!

Stepper Motors

A full rotation of a stepper motor is divided in a lot of steps which gives the motor the name. You can find several types of stepper motors:

(Image 1 is taken from: https://reprap.org/wiki/NEMA_17_Stepper_motor)

1. Permanent magnet stepper

A permanent magnet stepper motor composes of a stator and rotor which is a permanent magnet. The concentrating windings on diametrically opposite poles are connected in series.

2. Variable reluctance stepper

The rotor of a variable reluctance stepper motor consists of a serrated soft iron core. The magnetic field disappears after switching off the electricity. The stator and the rotor of the motor are aligned in a way that the magnetic reluctance in minimal. 

3. Hybrid synchronous stepper

The hybrid stepper motor combines the positive characteristics of both designs, permanent magnet and variable reluctance stepper with fine step division and good torque. 

National Electrical Manufacturers Association (NEMA)

The American company „National Electrical Manufacturers Association”(NEMA) has standardized a series of stepper motors. The all work with 200 steps per revolution. For our project, we used the bipolar NEMA 17 which is 42 x 42 millimeters. Down below you can find a list with several types of NEMA stepper motors that I took from Wikipedia.

NEMA 08, 20 mm × 20 mm, 0,036 Nm

NEMA 11, 28 mm × 28 mm, 0,1 Nm

NEMA 14, 35 mm × 35 mm, 0,3 Nm

NEMA 17, 42 mm × 42 mm, 0,5 Nm

NEMA 23, 47,14 mm × 47,14 mm, 2,0 – 4,0 Nm

NEMA 34, 86 mm × 86 mm, 4,5 – 8,0 Nm

The difference between unipolar and bipolar motors is that a unipolar stepper motor has one winding with center tap per phase, whereas a bipolar motor has a single winding per phase.

Difference between stepper motors and servo motors

Stepper motors and servo motors differ in two major ways: Their basic design and how they are controlled. Both serve to bring mechanical drives in a specific position. 

Stepper motors have a lot of poles (50 to 100). In comparison, servo motors have just a few (4 to 12 in total). The large number of poles allows a stepper motor to move accurate between each pole and allows a stepper motor to be operated without any position feedback for many applications. This means that moving a stepper motor to a precise position is much easier than a servomotor. So that is the reason why we used a stepper motor.

Servo Motor                                             Stepper Motor

(Image 2 is taken from: http://plcautomationparts.com/products/hc-pq033-mitsubishi/)

(Image 3 is taken from: https://www.omc-stepperonline.com/it/nema-34-cnc-motore-passo-passo-7-07nm-1001oz-in-86x86x98mm-8-fili.html)

How we controlled a stepper motor

There are some information you need to know so that your project works.

At first a stepper motor needs external power because of its construction. We just used a laptop power adapter.

 

Then we took a RAMPS 3D printer kit which contains the RAMPS (2), the driver/board (4) and cooler (1) because our concept is like a 3D-printer and it is much easier to use the kit. Just put the board on an Arduino Mega and it works 🙂

Here you can get some information about the kit.

There are different ways to connect a stepper motor with the board. Down below you can see the pins we used in the code and on the board as you can see in the pictures.

  

(Image 5 is taken from: http://domoticx.com/arduino-mega-shield-ramps/)

Here the pins in the code:

 

linked categories 2018b, Tutorials

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