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IndustryArena Forum > CNC Electronics > General CNC Machine Related Electronics > Electronics distribution best practices? (3--> 5 axis)
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  1. #1

    Electronics distribution best practices? (3--> 5 axis)

    Hi everyone,

    I'm building a 5 axis (first starting with a 3 and upgrading it, actually) router/light milling machine. I've got an EthernetSmoothStepper with a C82 board from CNC4Pc controlling 4 integrated servo motors (StepperOnline iSVS7T) in closed-loop mode with a 1.5kw spindle driven by a chinese VFD. Everything will be driven by mach4.

    I plan to build the electronics architecture for the full 5 axis (actually 6 axis because of the dual Y ballscrews, I guess) but wait on the BC head. Once I get the 3 axis all running and dialed-in, I'll finish the design and fab of the BC head, and go to 5 axis.

    My question is: Are there best practices for where to distribute the electronics? For example, I've read that you don't want the VFD near the signal lines or even in the same enclosure if it can be helped (is this a good idea? saves me money on large expensive Din-Rail boxes, I guess).

    I'll be running the whole system off of 220VAC, splitting off the AC power for the VFD/Spindle, then powering the ESS and other logic with 24V via a dedicated supply and including a third 48V supply to power the servos. One nice thing about the integrated servomotors is that I can run higher gauge power wire from the single 48v, 21A supply to a distribution box near the Z axis to power all of the servos on the gantry, and then use cat5 cables for the signals.

    I plan to take advantage of the RJ45/Cat5 wiring scheme of the CNC4Pc boards and do differential signals from the controller board to the servos to further reduce interference (if it is a problem). There will be 4 servo signals in close proximity (after addition of the BC head), but I reasoned that since they are step/dir signals and run differentially, that there should be minimal crosstalk problems.

    Is there something that I'm missing?
    Thanks!
    Brian

  2. #2
    Member
    Join Date
    Nov 2013
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    1540

    Re: Electronics distribution best practices? (3--> 5 axis)

    Hi,
    I run an ESS and have done for years. I've had very few issues with electrical noise.

    The only time I've had noise issues is when I push the VFD to 75% or higher. In the event I put a line reactor on the input oft he VFD and that solved it.
    The problem is that VFDs draw a lot of current and particularly harmonic currents. These currents will impress themselves on the incoming 230VAC supply
    and thereby pollute the power supply to your PC, your ESS , 24V and 48V supplies.

    I'd recommend a line reactor of 5mH to 10mH at the input of your VFD. I would also recommend two stage EMI filters on the 230VAC input
    to your PC, your ESS 5V supply and each of the other supplies.

    https://nz.element14.com/corcom-te-c...ase/dp/9586474

    Most people think shielding and earthing is the solution to electrical noise often overlooking that 'conducted' electrical noise is by far and away the most direct source
    electrical noise to your noise sensitive components.

    Craig

  3. #3
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    Jan 2018
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    1097

    Re: Electronics distribution best practices? (3--> 5 axis)

    Quote Originally Posted by brianthechemist View Post
    Hi everyone,
    I plan to build the electronics architecture for the full 5 axis (actually 6 axis because of the dual Y ballscrews, I guess) but wait on the BC head. Once I get the 3 axis all running and dialed-in, I'll finish the design and fab of the BC head, and go to 5 axis

    I plan to take advantage of the RJ45/Cat5 wiring scheme of the CNC4Pc boards and do differential signals from the controller board to the servos to further reduce interference (if it is a problem). There will be 4 servo signals in close proximity (after addition of the BC head), but I reasoned that since they are step/dir signals and run differentially, that there should be minimal crosstalk problems.
    Is there something that I'm missing?
    Thanks!
    Brian

    Just an idea....
    Cat6A shielded cables would be a better option (stranded, not solid core type).
    Because... If you get noise on the signal wires you can cut the sheath and strap them to you control box to shield the wires.
    You don't have the ability to do this with Cat5.

    I'm using Cat7 (solid core) with metal RJ45 ends for non motion areas strapped to the control box and out through grommets.
    I have small custom modules on mine with metal RJ45 sockets though with short dupont wires to my controller I/O
    This kind of thiing: https://www.amazon.co.uk/Connector-B...94HSL3DJ&psc=1

    Beings as the C82 has plastic RJ sockets, pre made Cat6A cable is your best choice, Cat7 not worth the hassle. Cat5 can't shield.

  4. #4
    Community Moderator Al_The_Man's Avatar
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    Dec 2003
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    23820

    Re: Electronics distribution best practices? (3--> 5 axis)

    I have my share of electrical enclosures over a period of time, and generally the rule is to place heat producing items at the top of the enclosure, along with respective fusing.
    Set up a decent star ground where all ground conductors are referenced to including the service earth GND.
    Carry out equi-potential bonding of the machine to prevent spurious interference etc.
    You should be able to find a copy of NFPA79 (Electrical wiring for Industrial equip) out there on the web.
    Per Murphy's law, you always end up with an enclosure ~5% smaller than originally estimated.
    CNC, Mechatronics Integration and Custom Machine Design

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

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