stepper motor

Discussion in 'General Electronics Chat' started by electronis whiz, Jul 3, 2011.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
    27
    i have a few stepper motors and some have 4 wires others have 6 so i googled it wikipedia said 6 wired ones are bipolar and 4 are unipolar.
    but bipolar is simpler to use because windings don't need to be reversed.
    i want to know if this is acurate because to me 4 wire seems more common and looks like it would be eiser to use.
    i have seen stepper controlers in catologs but there all made for industrial motors and are like 60-80$. is there any schmatics or anything farly simle like transistor a transistor circuit i can use to driven it. i have thought about using a brushlees fan motor controler to run a stepper but i am not sure if this wouldn work. i have got steppers to run but it was a dc motor connected to a shaft of a big stepper conected by wire to a smaller stepper. how do you know what lead is what on a steper and witch order they need to run in
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,795
    951
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    You have it all backward! 4 wire steppers are bipolar and 6 wire are unipolar but can also be ran as a bipolar. The circuit for driving a unipolar is the simplest. The bipolar is the one that takes a H-bridge and reverses the flow of electricity.

    A fan controller won't operate any stepper motor.

    Here is a link to both kinds of stepper motor controllers in kit form; http://www.electronics123.com/s.nl/sc.8/category.36/.f

    Here is a link that explains how stepper motors and drivers work; http://www.cs.uiowa.edu/~jones/step/

    To just get a stepper to turn , a kit is the way to go. It will be easier than trying from scratch(or some ones schematic that may not work). And all the parts are included even the pcb. And it is usually cheaper in the long run.
     
    Last edited: Jul 3, 2011
    electronis whiz likes this.
  4. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    I like to work with stepper motors that come with five wires. They are the easy ones to work with. With an ohm-meter I can figure out which is the common wire. The rest are just four windings which I can figure out by trial and error, usually they are colour coded. All you need is a two-bit gray code (0-1-3-2) to step the motor. Two bits output from an MCU, a couple of inverters and four power transistors and we're stepping!
     
    Last edited: Jul 5, 2011
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
    27
    so if i get a bi polar controler i can use it to drive both types of steppers?
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    no, They are different driving techniques.
     
  7. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Some six wire unipolar motors have essentially two centertapped windings, where the two centertap leads connect to power and the four ends are pulled low by the controller transistors in the pattern that rotates the rotor. If you leave the centertap windings unconnected, these can sometimes be controlled by a bipolar controller.

    But there are are hundreds, probably thousands of variations of stepping motors, so there are no guarantees that any particular motor will work the way you want it to.

    If you want to experiment with the six wire motor, use an ohmmeter to figure out which leads are the centertaps. Connect them to five volts through a resistor that will limit the current to maybe 100 milliamps, then you can use your hands to short the four remaining windings to ground, one by one. You should be able to find the pattern that makes the shaft rotate around step by step.

    That will help you get an understanding of the drive process.

    You can buy little discrete H-bridge stepper driver chips from parts suppliers like Digikey for about seven dollars that will drive small bipolar motors. They need about 12 volts and step and direction digital inputs. Usually they have also have pins to control half-stepping vs. full-stepping modes and to control the drive currents. That could get you started.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    While the 6-wire unipolar stepper motors can be driven by bipolar stepper motor drivers, you'll frequently suffer a performance "hit" due to the center-tapped coils having twice the inductance when driven in that mode. To overcome the inductance, you'd have to use a much higher voltage to drive the steppers; otherwise their performance would be quite sluggish.

    Unipolar motors are much easier to drive than bipolar motors, as you don't have to reverse the direction of current flow; just connect the center taps to your +V supply, and connect each of the "ends" of the coils to ground using transistors or MOSFETs in sequence in order to get the motor to rotate.
     
Loading...