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  1. Brad1979

    Lenz's Law pictorial

    electricpete, Very nice write-ups on how force in electric machines acts on the magnetic material instead of the conductors. You would be happy to know that "Electric Machinery" by Fitzgerald, Kingsley, and Umans makes this point in their textbook. This textbook seems to be a pretty standard...
  2. Brad1979

    BLDC for outer space aplication

    You are worried about performance when what you should be worried about is the environment. Make a list of all your requirements and send them to motor manufacturers. They will find the right motor for you or they will tell you how much it will cost to make the right motor for you or they will...
  3. Brad1979

    Article on Brushless Motor Terminology

    Nice article. Have you read James Mevey's thesis "Sensorless Field Oriented Control of Brushless Permanent Magnet Synchronous Motors?" In it he has a nice section discussing terminology. He did a literature search and found the brushless PM motors have been called the following names: BACM...
  4. Brad1979

    Motor Parts

    Like I said (twice already), you are probably right. It is very common for 4 coils per phase like this to be used to create 4 poles. All I'm saying is that this is not the case in general and one shouldn't confuse the number of coils per phase with the number of poles. What determines the...
  5. Brad1979

    Motor Parts

    theode, As I said, you are probably right. But you said "They are connected to give a polarity of north pole,south pole,north pole,south pole." How can you see that from the picture? You can't. How each individual coil is connected to each other is unknown at this point. The most probable...
  6. Brad1979

    Motor Parts

    Also, the copper windings and steel that surrounds the windings is usually referred to as the "stator." It generally isn't called an "electromagnet" when talking about a motor.
  7. Brad1979

    Motor Parts

    Sycorax, This is an AC induction motor ... there are no permanent magnets. The rotor is commonly called a "squirrel cage" rotor. It has laminated steel with cast aluminum in the slots of that steel. The rotor won't tell you how many poles there are. On AC induction motors, the number of...
  8. Brad1979

    Motor and ESC Theory - Current Draw

    Equation 23 on page 20 was the relationship that I was recalling.
  9. Brad1979

    Motor and ESC Theory - Current Draw

    0.79 = pi/4 ... correct? Why was I thinking the relationship was Ke=0.866*Kt?
  10. Brad1979

    Motor and ESC Theory - Current Draw

    Well, it's going to depend on the switching frequency of the PWM, the motor speed, the motor inductance and the motor resistance. But in general, during steady state operation, the current will "oscillate" around the 40 Amps. By "oscillate" I mean that the current will rise exponentially...
  11. Brad1979

    Motor and ESC Theory - Current Draw

    It's going to do neither of your 2 options. It has to pull 40 Amps because your torque stays the same. And the current isn't going swing from 80 Amps to 0 Amps because the motor's inductance is going to make it resist fast changes to the current.
  12. Brad1979

    BLDC Gear Motor

    Usually that is something you would get from your supplier. Asking for somebody else's DFMEA kind of defeats the purpose, doesn't it?
  13. Brad1979

    Submerged Motor

    The test condition for IPX8 only says that it is between the manufacturer and the end user but that it is at least severe as IPX7. So IPX8 doesn't guarantee that they have to run underwater, either.
  14. Brad1979

    Submerged Motor

    I would search for IP67 motors rather than "waterproof" or "water tight" motors or any other other key words like that. "Waterproof" means whatever the manufacturer wants it to mean. IP67 means the motor is protected to a depth of 1 meter for at least 30 minutes.
  15. Brad1979

    PMSM control strategy

    Just thought I'd link to this article about some of the reasoning behind why Tesla uses an induction motor.
  16. Brad1979

    Single phase motor Torque / Speed Curve.

    Good. I was being facetious but there is always the worry that people won't realize that. Anyway, I hope people realize that yes, you need to be clear and precise in your communication with others but being fastidious with respect to spelling/grammar/etc. can be just as bad for communication...
  17. Brad1979

    Single phase motor Torque / Speed Curve.

    And I was just pointing out that mw is neither megawatts nor, as you said, milliwatts.
  18. Brad1979

    Single phase motor Torque / Speed Curve.

    Actually, the correct abbreviation is mW.
  19. Brad1979

    Selecting a DC Motor

    Totally enclosed does not imply dust-proof.
  20. Brad1979

    Selecting a DC Motor

    A DC motor's speed is proportional to voltage, not frequency. PWM changes the speed of the DC motor by changing its effective voltage. PWM can affect the motor's torque. I've seen a motor's torque rating cut in half by using a PWM drive. If you're sure this is the size motor you need, then...

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