Stepper motor question

Discussion in 'General Electronics Chat' started by mrel, Sep 25, 2013.

  1. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hello
    Bipolar stepper motor has 4 wires,Unipolar stepper motor has 5 to 8 wires or more.
    Question is can a stepper motor only have just 2 wire?
    If a stepper can have just two wires how is it control?
    mrel
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    No stepper motor I've ever seen has only 2 wires.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,984
    3,223
    To get rotation in an AC motor you need a rotating field which generally requires more than one-phase which takes more than two wires. (An induction motor is a notable exception since it induces a rotating field so it will run, although not start, on a single-phase.) Stepper motors are not induction motors and require at least two phases (four wires) to run properly.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    The way it works is whether off or a DC applied, the tendency is for the rotor to sit under a nearest pole, when DC is applied, the motor will tend to stay with this pole up to the rated torque required to shift it off, the next pole requires to be energized at the same time removing power on the 1st pole, the motor will then step.
    More than two wires.
    Max.
     
  5. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    130925_171611.JPG

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    Since might not be a stepper motor i enclosed picture of the motor in pieces.
    The big round part is the case for the motor,the second is a small round piece which is a magnet go inside the case.
    Than there is blue round piece goes inside the case that has winding of copper wire solid copper wire with a very thin insulating layer,attach at each end is 18 gauge wire.
    Maybe with the pictures someone might know what kind of motor it is.
    This motor came off antenna made in china.
    Picture of antenna is enclosed.
    mrel
     
  6. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Don't know wha type of motor it is, but it's not a stepper.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Wow that's an unusual motor for sure!

    I've seen some similar mechanisms in clocks, if it is the same it is a single drive phase sequential motor with half phase magnetic detents;
    0 phase = rotor pulls to steel detent
    1/4 phase = +coil current
    1/2 phase = rotor pulls to steel detent
    3/4 phase = -coil current

    The perm mag rotor pulls to the magnetic detents (the bent metal tags) when no coil current is present. Then if the coil is powered + or - it rotates cw or ccw to about half the distance to the next mag detent.

    But that's just a guess, I have seen the principle in use but not in a "proper" motor, normally it is to drive slow speed very low load apps. Correct pulse timing and rotor inertia are needed.

    Alternatively it might be a very cheap and nasty synchronous AC motor?
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    It appears to be some form of variable reluctance motor, it must be able to index rather fine for aerial positioning, similar to used on my motorized FTA dish.
    Max.
     
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