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  1. #1
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    Brushed vs Brushless encoders

    Question from newbie:

    I'm trying to accumulate the components to build a cnc router table on the cheap. I have some brushed dc servo motors, and I'm looking for appropriate encoders.

    I have happened upon some encoders that are listed as "brushed dc servo motor encoders". I didn't realize encoders were specific to brushed or brushless motors. Is this actually the case?

  2. #2
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    What you need are incremental encoders, as opposed to absolute.

  3. #3
    Super Moderator Al_The_Man's Avatar
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    Quote Originally Posted by bdillard
    Question from newbie:
    I have happened upon some encoders that are listed as "brushed dc servo motor encoders". I didn't realize encoders were specific to brushed or brushless motors. Is this actually the case?
    Brushless encoders are usually specific to a certain motor , especially if they have commutation tracks on them.
    For DC Brushed motors just about any kind of encoder can be used, even Brushless encoders as they usually contain the quadrature output as well as the commutation, which can be ignored.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  4. #4
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    Quote Originally Posted by H500
    What you need are incremental encoders, as opposed to absolute.
    Thank you, but that confuses me even more. I am looking at the Tamagawa OIH35 series. Tamagawa has this encoder listed as an incremental encoder, but has it listed for brushless dc applications.

  5. #5
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    Thank you Al, and H500.

  6. #6
    Super Moderator Al_The_Man's Avatar
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    Quote Originally Posted by bdillard
    Thank you, but that confuses me even more. I am looking at the Tamagawa OIH35 series. Tamagawa has this encoder listed as an incremental encoder, but has it listed for brushless dc applications.
    That is because it is probabally an incremental encoder with DC brushless commutation tracks. The commutation tracks are read by the amplifier and the encoder is used by the controller for positioning.
    If you have DC brushed motors you don't have to worry about commutation, just the incremental part is all you use.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  7. #7
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    Just to answer your question, there is no such thing as a as "brushed dc servo motor encoder". For a brushed motor, you just need a generic incremental quadrature encoder. It must have 2 tracks, and optionally, an index track. An encoder for a brushless motor will have commutation tracks. Many of them also have incremental quad encoder tracks and an index track, so you could use them if they are cheap.

    When buying encoders on ebay or surplus, you pretty much have to read the data sheet, because there are so many options, and many encoders are worthless except in a very limited application.

  8. #8
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    Take a look at the Agilent (Avago) HEDS series of encoders. Unless you find a better deal on Ebay, I believe they are the most cost effective high res encoders currently available.

  9. #9
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    Thank you. I managed to stumble upon the HEDS series and also US Digitals E6 series. They look very similar, and I suspect either will be suitable. Thanks again for the help; it saved me from making an impulsive mistake.

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