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Stepper motor stepping uniformity

  1. Aug 10, 2009 #1
    Hello,

    Recently,I got 2 stepper motors,one which was dismantled from a blood analyzer machine and the other one was bought from a local store.

    The stepper motor spec from the machine is:
    12V dc
    1.8 degree resolution
    1A

    The stepper motor spec bought from the store is:
    12V dc
    1.8 degree resolution
    500 mA

    I wish I could provide more information but the datasheet is not available. The one which I got from the local store is very cheap approx 1/10 of the price from major electronic retailers.So I assume it is of inferior quality. And there is no spec available from the store too.

    The other one was dismantled from an expensive analyzer machine.So i guess it is of good quality.

    Now I tested both stepper motors using the same circuit (unipolar manual switch tester).I notice the cheap stepper motor steps are not uniform.Some steps are bigger and some are smaller. I tested them using clockwise and counterclockwise.

    For the good stepper motor, the stepping are all uniform.

    I didnt measure the stepping degree but i can see very clearly the stepping degree of the cheap stepper motor are not the uniform.For example,the second step is smaller than the first step.

    Can anyone explain why the cheaper stepper motor steps are not uniform?I am sure the sequence is correct and the same sequence is tested for the good stepper motor.

    Thank you.
     
  2. jcsd
  3. Aug 10, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    I've not come across that problem before. Any chance your simple step driver circuit is bouncing or having other issues with the one motor? Are the steps multiples of the 1.8 degree step, as if it is double- or triple-stepping sometimes?

    If you just put an oscilloscope on the input leads (no driver connected), and spin the motor by hand (or better yet with a constant speed motor), do you see any difference in the output waveforms between the two motors?

    http://en.wikipedia.org/wiki/Stepper_motor#Microstepping

    .
     
  4. Aug 10, 2009 #3
    There should not be any problem with the circuit because i used the same circuit to test another stepper motor which i got from the blood analyzer machine.

    I am using wave drive mode,energizing 1 phase at a time in clockwise and counterclockwise sequence.

    I can clearly see the stepper motor which i bought from the store (cheaper one) did not show uniform steps.For example,step 1 big step,step 2 smaller step and step 3 big step and etc.

    The same circuit was used to test the stepper motor from the blood analyzer machine and it showed uniform steps.


    Any clear explaination what might be the issue?Or can I just say that the cheap stepper motor is lousy?
     
  5. Aug 10, 2009 #4

    berkeman

    User Avatar

    Staff: Mentor

    I don't think you understood what I was trying to say. Are the "big" steps equal to two regular steps? If so, there could be a problem interaction between the motor and the drive circuit. Just because the drive circuit works with one motor, doesn't mean it necessarily will work with another motor of a different size.

    Have you watched the motor drive signals with a multi-channel 'scope? Have you tried the turning experiment that I mentioned?

    The two motors likely have the same internal construction, with differences in current capacity and bearing quality. If they both are labelled witih the same 1.8 degree per step size, they both should be able to accomplish that.

    Have you tried a 2nd cheap stepper? Maybe that one you have has some internal wire shorting issues...?
     
  6. Aug 10, 2009 #5
    Thank you for the reply.
    I guess I will need to test it to find out what is the root of the problems.
     
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