Stepper Motor Problem

Discussion in 'The Projects Forum' started by DanRilley, May 25, 2009.

  1. DanRilley

    Thread Starter Senior Member

    Jan 13, 2008
    107
    0
    Hi, I am experimenting using a stepper motor with an arduino microcontroller. I am following this basic setup:

    [​IMG]

    I am using microcontroller code that rotates the motor 100 steps forward and then 100 steps backward.

    The first two motions work very smoothly (forward and backward once) however, on subsequent rotations I can hear a clicking from inside the motor and it is very jittery, as if the wires were hooked up incorrectly. But, I assume they are correct because the first 2 turns work.

    The motor is a mitsumi m42sp-6nk, pulled out of a printer. I am guessing that this is the 12V version of this motor, although there is both a 24V and a 12V in existence. Would this be the effect if I was powering a 24V motor with only 12V?

    Any idea what the problem might be. I am also noting that the motor driver chip is getting *very* hot. I am feeding 12V into the motor-in but it should be within range. This is my first motor project so I expect I have just missed something very simple.

    Thanks.

    P.S. also on the circuit diagram, all of the grounds go to a single ground, which I have done in my circuit. But I was wondering, does the motor power supply need to have a separate ground from the microcontroller power supply, since one is 5V and the other is 12V?
     
    Last edited: May 25, 2009
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The clicking or chattering behavior you describe sounds like you are momentarily driving both of the coils in a mode that causes them to work against each other for control of the motor.

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Did you look at the datasheet for the stepper motor?
    http://www.mitsumi.co.jp/Catalog/compo/motor/m42sp6nk_e.html
    Note that it's rated for 400mA peak current when using a chopper driver (such as an L297/L298 pair), and that the coil resistance is nominally 5 Ohms per phase.

    If you wish to drive the motor using DC current (without the chopper drive), you'll need to limit current to 400mA.

    A glance at TI's datasheet for the SN754410 indicates that at 500mA, the driver will drop roughly 1v each for the high and low sides. If your supply is 12v, that leaves 10v for the stepper motors.

    Since the stepper's coils are nominally 5 Ohms, 10v/5 Ohms=2 Amperes. You're way over their current specifications; both the motor and the driver IC! No wonder the IC is getting hot! :eek:

    Let's re-calculate what you need for your supply voltage. E=IR, so Supply Voltage = 400mA x 5 Ohms + 2v (dropped across the driver) = 2v + 2v = 4v.

    So, you actually need a 4v supply for the stepper.

    Get the supply voltage correct. Then double-check that your code is doing the right things at the right time.
     
  4. DanRilley

    Thread Starter Senior Member

    Jan 13, 2008
    107
    0
    Hey SgtWookie, I will try this today. Truthfully a lot of that is a bit over my head and I'm going to have to go over it a few times before it sinks in (I just saw 12V on the spec sheet and went for it...oops). I'll try it at 4V and see what I get, thanks for the help!
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK, read it through a few times.

    Keep in mind that the performance won't be as good using straight DC and your driver IC as it would be if you were using a chopper driver like the aforementioned L297/L298 ICs. The idea with the chopper driver is that the current flow in the stepper's windings is established much more rapidly than using just straight DC. Your torque at speed will be less, and you won't be able to step the motor as quickly as if you had used a chopper driver.
     
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