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  1. #21
    One of their downsides is that I think brushed DC servos are used - so they will have a finite life, I will swallow that
    At least the brushes appear to be easily externally accessible - so easy to change I would guess.

    Do those motors have integral brakes? If not, you might need to add one on the Z axis if you're going to run a big fat (end hence heavy ) spindle - servos don't have the stiffness that steppers have when the power's off, and depending on gearing etc., you might get a slowly drooping spindle when you switch off.
    Last edited by Voicecoil; 20-04-2019 at 08:57 AM.

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  3. #22
    Quote Originally Posted by Voicecoil View Post
    Do those motors have integral brakes?
    An excellent point which I had not considered! Unfortunately no brake.

    I plan to use the following 3.5kW spindle and VFD:
    https://www.aliexpress.com/store/pro...1bdf23a8f7ed5m

    https://www.aliexpress.com/store/pro...2e6c275cpko9w1

    At 8kg, this spindle may well cause problems.

    I will most likely use a fairly high gear reduction on the Z (maybe 5:1 or even higher as compared to 2:1 on X/Y). Perhaps this will amplify any holding force/friction enough to keep it in place when powered off. If it does turn out to be a problem I guess I could always buy an external brake like this (though I won't have a convenient 24v supply for it, nor will I know how to connect it, maybe using a relay on the BOB or something...)
    https://www.zappautomation.co.uk/24v...brake-2nm.html

    I'm also not particularly happy about the C10/C11 breakout board that comes with the kit. The wiring diagram is a bit scant and I am not sure it has all the features I need for spindle control - and I don't know what a charge pump is, or if I need one, but it doesn't seem to have one.

    If I am feeling up to it I may use the kit as an inspiration to piece together my own system using some more custom parts - but I'm already overwhelmed by the complexity of all this!


    Quote Originally Posted by Voicecoil View Post
    you might get a slowly drooping spindle when you switch off.
    That's what she said

  4. #23
    FY! a charge pump is an electronic circuit that's usually used to generate a low-ish power but higher DC voltage from the existing DC supply using capacitors, rather than an inverter/transformer/boost converter arrangement - e.g. generating 10V from a +5V supply.

    That's what she said
    lol
    Last edited by Voicecoil; 24-04-2019 at 07:50 AM.

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  6. #24
    I've created a build log where I can press ahead with my ideas: would welcome any more comments you guys may have!

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