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Relating Stepper Motor Current To Torque

Discussion in 'Embedded' started by Ted Wood, Dec 17, 2003.

  1. Ted Wood

    Ted Wood Guest

    I'm looking to measure the torque generated by a stepper motor by
    relating it to winding current during steps. Has anyone done anything
    like this or can anyone suggest some references?

    I reckon the main problem will be change in winding resistance with
    temperature - is this correct?

    Cheers
    TW
     
    Ted Wood, Dec 17, 2003
    #1
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  2. Ted Wood

    CBarn24050 Guest

    Hi, winding resistance will make no difference. Torque is proportional to
    current, it drops off with motor speed. You should be able to get a graph for
    your motor from the data sheet.
     
    CBarn24050, Dec 17, 2003
    #2
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  3. Ted Wood

    Tauno Voipio Guest

    For any high-performance stepper drive, the coils have to be fed from a
    constant-current source. It makes the point of winding resistances moot. The
    winding resistance only sets a requirement for minimum voltage-compliance of
    the current sources. In any reasonable system, a more significant part of
    the compliance requirement comes from the back-EMF of the motor (caused by
    rotation speed).

    If the current sources are implemented as direct series-pass linear
    elements, the power dissipation in the current sources usually is many times
    the motor power, so in a system with more than a few watts of power, the
    current sources have to be built as switchers.

    HTH

    Tauno Voipio
    tauno voipio @ iki fi
     
    Tauno Voipio, Dec 17, 2003
    #3
  4. [...]

    How were you going to measure torque? I have an idea to build a small
    dynomometer - one of those projects that will probably never happen.
    I have the equipment, but putting it together is a challenge.

    This involves using a good brushless DC servomotor and digital drive.
    The drive needs to be able to operate in a torque mode and provide output -
    probably in the form of an analog out or streaming data that corresponds
    to the various drive parameters - speed, torque, etc.

    Hook the motor to be studied up directly to the torque drive. Create
    estimates of the viscous and dynamic drag of the servomotor. Adjust the
    torque of the servo to observe the curves of the motor under study.
     
    Bryan Hackney, Dec 28, 2003
    #4
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