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Thread: PM-932m CNC Conversion

  1. #13
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    Default Re: PM-932m CNC Conversion

    Test fitting a NEMA 4 enclosure sized 20" x 20" x 10", with 3 x DMM DYN4 AC Servo Drivers inside the box.

    I probably won't put the NEMA enclosure on the mill itself, but it gives you an idea of the scale.

    Also added the DMM 750W AC servos on the X/Y axis.


    PM-932m CNC Conversion-pm-932m-v6-jpg

    PM-932m CNC Conversion-pm-932m-v6-front-jpg

    PM-932m CNC Conversion-pm-932m-v6-right-jpg



  2. #14
    Member ninefinger's Avatar
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    Default Re: PM-932m CNC Conversion

    I'd ask DMM for their recommendation on controlling the servos. They take step & direction inputs so may be better with a "stepper" control board rather than a servo control board. The drives themselves handle the feedback from the encoder, not the control board so no need for that on the control. Also, look at the ethernet MESA cards, (7i76e), card can go in the control box and the PC can be completely separate, connected with a dedicated ethernet cable. Lets you use almost any format PC and not have to have a slot for the card. Plus the 7i76e has lots of IO, no real need for another card right away.



  3. #15
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    Default Re: PM-932m CNC Conversion

    Quote Originally Posted by ninefinger View Post
    I'd ask DMM for their recommendation on controlling the servos. They take step & direction inputs so may be better with a "stepper" control board rather than a servo control board. The drives themselves handle the feedback from the encoder, not the control board so no need for that on the control. Also, look at the ethernet MESA cards, (7i76e), card can go in the control box and the PC can be completely separate, connected with a dedicated ethernet cable. Lets you use almost any format PC and not have to have a slot for the card. Plus the 7i76e has lots of IO, no real need for another card right away.
    Thanks for the feedback.

    I looked at the Ethernet stepper board, but kind of decided against it because it didn't appear to have the encoder feedback with steppers (?).

    I thought it was important that LinuxCNC have the feedback from the servos so it can do its own servo driving with PID loops.

    So I'm going to start with the PCIe card... And maybe if they ever release a Ethernet servo board I might switch to it then.

    Sent from my Pixel 3 XL using Tapatalk



  4. #16
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    Default Re: PM-932m CNC Conversion

    I found a like-new Hoffman CSD202012 (20x20x12") NEMA 4 enclosure on eBay for about $100, plus the panel board (sold separately) for another $40, so I'm going with that size.

    Hoffman also has excellent 3D STEP models of their products, so that's also helpful.


    It's big enough that I might be able to fit a Mini-ITX board in there for the CNC computer.

    I have two Mini-ITX boards lying around, an older Intel Avoton C23750 fanless board, and another with an Intel Xeon-D server processor - also low power.

    PM-932m CNC Conversion-csd202012-v4-front-jpg



  5. #17
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    Default Re: PM-932m CNC Conversion

    Came up with a Y-axis motor mount that should allow me to re-use the existing hole for the ballscrew, with only drilling and tapping mounting holes required.

    The motor end has the DMM NEMA34 servo, a MBA15-F motor mount, the aluminum mounting block, and then a FK15 block for the threaded end of the ballscrew.

    The free end of the ballscrew will be supported by a FF15 block, mounted to a T-shaped aluminum block which should bolt to the underside of the casting.



    The Aliexpress store (TBI Motion) I'm looking at offers C3 ground ballscrews, and they also offer C3 class FK blocks with real Angular Contact bearings.

    I'm going to wait until the machine arrives so I can double-check the measurements before I order the ballscrews and such.


    PM-932m CNC Conversion-pm-932m-v3-y-servo-jpg

    PM-932m CNC Conversion-pm-932m-v3-y-axis-cut-jpg

    PM-932m CNC Conversion-pm-932m-v4-y-axis-free-end



  6. #18
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    Default Re: PM-932m CNC Conversion

    Quote Originally Posted by ninefinger View Post
    I'd ask DMM for their recommendation on controlling the servos. They take step & direction inputs so may be better with a "stepper" control board rather than a servo control board. The drives themselves handle the feedback from the encoder, not the control board so no need for that on the control. Also, look at the ethernet MESA cards, (7i76e), card can go in the control box and the PC can be completely separate, connected with a dedicated ethernet cable. Lets you use almost any format PC and not have to have a slot for the card. Plus the 7i76e has lots of IO, no real need for another card right away.
    Looking into this further, Mesa actually offers two other Ethernet boards that would work:

    • 7I95 Ethernet interfaced Step & Dir & encoder plus I/O Interface
    • 7I97 Ethernet interfaced Analog servo plus I/O interface



    Description for the 7i95:

    The 7I95 is a Ethernet connected motion control interface designed for interfacing up to 6 Axis of step&dir step motor or servo motor drives and includes encoder feedback for each axis. Step rates up to 10 MHz are supported. The 7I95 also has 24 isolated inputs plus 6 isolated outputs for general purpose I/O use. 6 high speed encoder interfaces are provided axis feedback and for spindle synchronized motion. Two RS-422/RS485 serial expansion ports and a parallel expansion port are also provided.
    All step and direction outputs are buffered 5V signals that can drive 24 mA. All outputs support differential mode to reduce susceptibility to noise. The encoders can be used with TTL or differential input.
    24 isolated inputs are provided for general control use including limit switch and control panel inputs. Inputs operate with 3V to 36V DC and can have a positive or negative common for sourcing or sinking input applications. 8 inputs can be used to support up to 4 quadrature MPGs.
    Six 36V 2A isolated outputs allow sinking, sourcing combinations of both.
    Two RS-422/RS-485 interface is provided for I/O expansion via a serial I/O daughtercard. In addition to the on card I/O, A FPGA expansion connector compatible with Mesa's 25 pin daughtercards or standard parallel port breakout boards allow almost unlimited I/O options including additional quadrature or absolute encoder inputs, step/dir or PWM/dir outputs, and field I/O expansion to hundreds of I/O points. All field wiring is terminated in pluggable 3.5 mm screw terminal blocks. The 7i95 runs from a single 5V supply.


    MesaUS.com doesn't list the card, so I may have to ask about it.



  7. #19
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    Default

    Quote Originally Posted by gmoschini View Post
    AC Servos

    Decided to splurge and go for DMM AC Servos and DYN4 drives:

    • 86M-DHT 0.75 kW AC Servo on X
    • 86M-DHT 0.75 kW AC Servo on Y
    • 86M-DHT 0.75 kW AC Servo with Brake on Z
    • 3 x DYN4 AC Servo Drives


    Cost: $1643


    The DYN4 AC Servo drives have the benefit that they can run directly off of single-phase 110/220V AC, so a DC power supply or an AC toroidal transformer isn't required.


    For controlling hardware, I'm going to with the Mesa electronics 7I77 6-Axis Servo control board, and either a PCI/PCIe 5i25 or 6i25 card and LinuxCNC.

    5i25-7i77 PCI Kit
    6825-7i77 PCIe Kit
    Look at EBay. I ordered my DMM servos and drives from them on Ebay. Saved a couple hundred and free shipping. I’m working on getting them up and running. I bought them for a PM45.



  8. #20
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    Default Re: PM-932m CNC Conversion

    DMM has some really fast shipping, the servo motors arrived today!

    PM-932m CNC Conversion-img_20191111_114309-jpg

    PM-932m CNC Conversion-img_20191111_114338-jpg

    PM-932m CNC Conversion-img_20191111_114404-jpg

    PM-932m CNC Conversion-img_20191111_115016-jpg

    PM-932m CNC Conversion-img_20191111_115434-jpg

    PM-932m CNC Conversion-img_20191111_115425-jpg


    Decided to cancel my order from MesaUS while I reconsider my controller options.


    I'm leaning towards one of these two:

    • Mesa 7i97 - Ethernet Analog Servo Control + Encoders
    • Mesa 7i95 - Ethernet Step + Direction Control + Encoders



    I think my preference will be for the 7i97, analog servo control...


    However I did send an e-mail to DMM asking their feedback.



  9. #21
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    Default Re: PM-932m CNC Conversion

    After some further discussion with JT @ Mesa US I've decided to go with the Mesa 7i76E as originally recommended (good call!).



  10. #22
    Member ninefinger's Avatar
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    Default Re: PM-932m CNC Conversion

    Glad you talked to one of the 2 vendors - I think you'll be very happy with that setup.
    As far as the PC goes - you may want to have it closer to the screen depending on where the electronics box ends up. Otherwise you have to run multiple long cables to your screen and other input devices (mouse & keyboard, pendant, etc). If you have the pc near the screen its just the cat5e cable back to the electronics box (and maybe the AC power for it). Also makes it easier to plug in USB sticks unless you plan that out in advance too.



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    Default Re: PM-932m CNC Conversion

    Quote Originally Posted by ninefinger View Post
    Glad you talked to one of the 2 vendors - I think you'll be very happy with that setup.
    As far as the PC goes - you may want to have it closer to the screen depending on where the electronics box ends up. Otherwise you have to run multiple long cables to your screen and other input devices (mouse & keyboard, pendant, etc). If you have the pc near the screen its just the cat5e cable back to the electronics box (and maybe the AC power for it). Also makes it easier to plug in USB sticks unless you plan that out in advance too.
    I will probably have the PC initially set up on its own cart, with the connection to the CNC control box being via the ethernet cable.


    I have an older Asrock C2750D4I Mini-ITX motherboard that I'm thinking of using as the PC's guts.

    Maybe with a Mini-ITX case that can be VESA mounted on a monitor arm...

    The motherboard is fanless, and has the benefit of having 2 x LAN ports - one for internet access, and the other for the CNC control.



  12. #24
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    Default Re: PM-932m CNC Conversion

    I also have one of these Supermicro X10SDV-TLN4F Mini-ITX boards that I modified with a copper finned heatsink...

    But this board is massive overkill...


    The other C2750 board may be fine, but I'm also concerned about the lack of USB ports (3 max), and I'd rather not have to do USB hubs...

    Maybe one of those J1900-style ultra compact PCs?



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