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  • Step Motor Heating

    Oct
    28

    In our last post, we showed that you can get more torque at higher speeds if you operate a motor at a higher voltage.  In the example below, the red curve, measured at 70 VDC, provides much better high speed torque than the orange (12V) curve.   So why not always use 70 volts?  Better still, why not apply 100 volts and really flatten out that curve?

  • What is Step Motor Stack Length?

    Oct
    28

    In our post What Do NEMA Sizes Mean?, we examined the NEMA frame sizes in which step motors are made. Larger frame sizes produce more torque. But this is not a one dimensional process: within a given frame size, the motor length can vary and that also affects torque. Because step motors require expensive tooling in order to be produced economically, a fixed rotor length is chosen, as is the stator that surrounds it.

  • How Does A Step Motor Work?

    Oct
    28

    Though it's long been rumored that step motors are driven by tiny hamsters on wheels contained inside, I can assure you that this is not only untrue, but also promulgated by unscrupulous pneumatic actuator salesmen.  So how does a step motor work? In reality, step motors operate by electromagnetism.  Specifically, a permanent magnet rotor such as the one shown below is attracted to electromagnets that reside in the stator.

  • What do NEMA sizes mean?

    Oct
    28

    Step motors are categorized by frame size, such as "size 11" or "size 23".  Ever wonder how that came to be or what it means?  The National Electrical Manufacturers Association sets standards for many electrical products, including step motors.  Generally speaking, "size 11" mean the mounting face of the motor is 1.1 inches square.

  • Dynamic Torque & Step Motor Sizing

    Oct
    28

    In the posts What Do NEMA Sizes Mean? and What is Step Motor Stack Length? we discussed factors affecting holding torque in step motors, such as frame size and stack length.  Holding torque is a measure of how much rotating force is required to force a stationary step motor shaft out of position.

  • How Do You Mount A Step Motor?

    Oct
    28

    If you are new to step motors, you may be wondering how to mount one in your application. You’ll need to be concerned with three things: piloting the motor, fastening it to the mounting surface, and coupling the shaft to your load.

  • Modeling a Step Motor Generator

    Oct
    28

    In our last post, we explored the possibility of connecting a step motor to a small gas engine for use in recharging a 12 volt battery. The effort resulted in a computer model which we hoped to use to optimize the design without having to expend excessive time and effort on trial and error. Our first concern was whether the step motor had the optimal number of winding turns on the stator. Changing the winding of a step motor is a difficult experiment because of the complexity of reprogramming a winding machine and loading it with a different size wire.

  • Measuring Power Dissipation in Step Motors and Drives

    Oct
    28

    Background In some applications, power dissipation in step motors and drives  is a critical aspect of system design. Too much heat from the drive can cause a cabinet to overheat. Too much power loss in the motor can cause the motor to overheat at high ambient temperatures. Heat can also transfer into attached equipment causing it to misbehave. One example is a digital ink pump, where excess heat from the motor can cause undesirable changes in the viscosity of the ink. A recent customer was modeling their enclosure and requested detailed power dissipation data.

  • What Is A Unipolar Step Motor Drive?

    Oct
    28
    What is a unipolar step motor driver? How does a unipolar driver compare to a bipolar step motor driver? When step motors first became popular as a simple, inexpensive means to control position and speed, the transistors required to drive them were very expensive. What, transistors expensive? Don’t they put, like, a billion of them on a chip?
  • Stepper Motor Accuracy

    Oct
    28

    Step motors are prized for their ability to provide precise positioning without a feedback mechanism or closed loop control system.  This inherent precision is owed to the fact that hybrid step motors have toothed rotors and stator that create an electromechanical gearing system to increase the resolution provided by rotating the stator field by 50X.  Move the field by 90° (one full step) and the motor shaft moves by just 1.8°.

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