DC motor

First, 7 things to consider when choosing an electric motor:

Choosing the right motor isn’t always straightforward. There are so many variables to consider that it can be hard to know where to start. The wrong motor can result in a myriad of problems, and can ultimately cause application failure.electric motor

(Here are) some initial questions that you need to answer before attempting to find the right motor for your project.

Questions you need to consider in choosing a motor:
  • Speed: How fast should the motor be able to run?
  • Torque: Which motors provide enough torque?
  • Size: What are the size restrictions?
  • Precision: Does the motor need to be accurate? How accurate?
  • Environment: What is the environment in which the motor will be running (is there dust, moisture, air flow, etc.)?
  • Communication: How do you want to communicate with the motor?
  • Cost: What is your budget?

  • Once you’ve come up with answers to these preliminary questions, you can begin to figure out the best option for your application.
    BLDC was coined as when using the standard "six step" energisation it really is very similar to the action carried out by the commutator in a brushed motor. The motor is of course an AC motor but in terms of the BEMF waveform shape it MAY (underlined!!) have been designed with a more trapezoidal BEMF which CAN (underlined!!) give a smoother torque compared with a sine BEMF and six step energisation.

    The current through the windings can be anything you want. Preferably you are driving a synchronous motor (that is NOT BLDC) with a sinusoidal current to get a sinusoidal voltage across the windings, what the synchronous motor is designed for. The current through the BLDC motor usually has the form of a "modified" square wave. The current through each winding is either steady positive, zero or steady negative. It is during the zero period you read the BEMF from that winding to establish the rotor location for a sensorless BLDC so you (that is the controller) can switch the current through the windings at the right time.
    A BLDC motor may have a trapezoidal Back EMF, there is something called Trapezoidal Motor Control Methodalogy (TRZ). TRZ is an extension of 6-step control with additional switching states generated to allow winding current to ramp up/down in each phase prior to/after each commutation instant. Trapezoidal motor winding currents, achieve a low noise performance.

    Brushless DC motors are generally, although not always, three phase devices. They are wired in either a Y (Wye, Star, T) or Δ (Delta) configuration, but in either case there are three connecting wires, and the current input to any two coils must be output through the third. That is,

    C = –(A + B) where A, B, and C are the current flowing through each leg of the 3-phase brushless motor.
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