Category Archives: Technical

Inductive effects on Motor Performance: Quantitative Analysis

At each commutation, energy is required to drive current into the phase that was previously unattached and is now attached to a power supply rail. The energy stored into the inductance is:  E=1/2LI2.  Energy has units of Joules and a … Continue reading

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The Effects of Inductance on Motor Performance: Qualitative Discussion

A brushless DC motors speed curve is reduced by the effects of motor inductance.  Below is a torque speed curve showing curves that both include and do not include the effects of inductance.   The red curves are the motor … Continue reading

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Motor Performance Curves

 Two performance curves are critical to defining the motor formants: the speed versus torque curve, and the current versus torque curve.  Developing the equation for motor speed versus torque curve starts with a motors back EMF constant, Ke. The simplest … Continue reading

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Defining the Motor Requirements

Unless the gearbox is already designed, the actuator gearbox should be designed concurrent with the motor selection.  This allows the overall system to be optimized.  What being optimized means depends upon application.  Optimal may mean lowest-cost, low size, or lowest … Continue reading

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Motor size constants

Motor size constants are fixed by the amount of steel and copper in a motor. No matter how the winding area is filled, size constants remain fixed. The most important motor size constant is Km, the motor constant. It has units … Continue reading

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Motor winding constants

Motor winding constants are changed by how the available copper space is wound.  For example if you already have a motor datasheet and the motor has a back EMF constant of 10 V per kRPM then you could modify the … Continue reading

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Motor constants

Motor constants fall into two groups: motor size constants and motor winding constants. Size constants are constants that are fully defined by the motor size.  These constants are the peak torque, thermal impedance and the motor constant, Km, which has … Continue reading

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Motors: Breaking the Laws of Physics

Once in a while I get asked why a motor can’t be designed that has a back emf constant, Ke, that is independent of the the torque constant, Kt.  If only I could.  I would solve the worlds energy needs.  Of … Continue reading

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