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  • How Can You Calculate Step Motor Trajectories?

    Oct
    28
    by Jeff Kordik

    Step motor motion is conceptually simple: Just rotate the stator field and the rotor will follow, so long as you don’t expect it to violate the laws of physics.  An easy but unpleasant way to violate said laws is to ask for more acceleration than the motor can achieve.  So how does one perform step motor trajectory calculations? As we learned in the post Dynamic Torque & Step Motor Sizing, maximum acceleration is determined by torque divided by inertia.

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  • How Does Holding Torque Differ From Pullout Torque?

    Oct
    28
    by Jeff Kordik

    The first thing many new users ask about step motors is: "what's the difference between holding torque and pullout torque?". Which one matters to me (as Herb Tarlek might say)? If you apply a constant current to one winding of a step motor, torque is produced according to this formula:

    torque_eqn

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  • Why Do Step Motors Get Hot?

    Oct
    28
    by Jeff Kordik

    In our post Step Motor Heating we looked at step motor losses over a wide range of speeds and power supply voltages. Now, we deepen our examination. Step motors waste power in two ways: copper losses that result from the electrical resistance of the stator coils and iron losses from magnetic hysteresis and eddy currents. In both cases, this lost power results in the motor heating.

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  • Step Motor Heating

    Oct
    28
    by Jeff Kordik

    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?

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  • What is Step Motor Stack Length?

    Oct
    28
    by Jeff Kordik

    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.

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  • How Does A Step Motor Work?

    Oct
    28
    by Jeff Kordik

    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.

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  • What do NEMA sizes mean?

    Oct
    28
    by Jeff Kordik

    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.

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  • Dynamic Torque & Step Motor Sizing

    Oct
    28
    by Jeff Kordik

    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.

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  • How Do You Mount A Step Motor?

    Oct
    28
    by Jeff Kordik

    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.

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  • Modeling a Step Motor Generator

    Oct
    28
    by Jeff Kordik

    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.

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