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  1. #11
    Yep.
    You want your step/dir signals wired differential.
    Using the open collector way like you would with steppers is no use.
    I was told OC is only good for 150khz reliably. So a breakout board that can wire differential is desirable to achieve the wanted 400khz such as the UB1.
    There are converter boards to go between the bob and servo that can convert OC wiring to differential but I've never tried them.

    Adjust the electronic gearing to suit whichever kHz setting is being worked with.

  2. #12
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 17 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 8,436. Received thanks 1,445 times, giving thanks to others 108 times. Referred 1 members to the community.
    Quote Originally Posted by dazp1976 View Post
    Yep.
    You want your step/dir signals wired differential.
    Using the open collector way like you would with steppers is no use.
    I was told OC is only good for 150khz reliably. So a breakout board that can wire differential is desirable to achieve the wanted 400khz such as the UB1.
    There are converter boards to go between the bob and servo that can convert OC wiring to differential but I've never tried them.

    Adjust the electronic gearing to suit whichever kHz setting is being worked with.
    Dazp suggests a good board because the UB1 is an excellent choice if you are using servos due to the fact its differential line drivers are nice and fast, however when you get into the 400khz + frequencys then everything becomes important.?
    Cables and grounding must be quality and done correctly otherwise any stray electrical noise will cause chaos. Noise is the main difference between single-ended and differential signals and why it's better to use differential signals when the frequencies start to go up above 200khz

    That said I don't think you will be using 400khz for 1500rpm motors unless they have very high count encoders. If they are using typical 2500 line quadrature encoders then you'll only need 250khz to reach 1500rpm which shouldn't cause you too much trouble and you could get away with using single-ended signals provided you use good grounding practices and careful cable routing away from electrically noisy components.

    However, I would still prefer going to the trouble of using differential signals with quality shielded cables and careful grounding than selecting a lower frequency and using electronic gearing at the sacrifice of resolution and smoothness.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

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  4. #13
    Thanks for the heads up guys!

    I'll be using the UC300ETH-Max, (UB-1+UD-1).

    I'm retrofitting an older machine, and want to keep the performance.
    So I want to keep 12000mm/min on the 4010 ballscrews, so 1200rpm on the servos.

    (1200rpm x 10'000ppr) / 60sec = 200khz.

    So if the 400khz was max combined, it would slow my total down, but since it is per axis, it is no problem.

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