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  1. #1
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    Aug 2015
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    6

    Motor_Controller_Design

    I ask for the help of CNCzone’s forum members to help me find the value of a motor control project idea.

    I value the opinion of people who are knowledgeable in machine control. Many of CNCzone’s forum readers (i.e. you) have experience a 3axis mill, 5 axis mills, or a 3D printer. What I would like from CNCzone’s forum is an idea if my hardware control design is worth the time, effort, and money to develop.

    My basic idea is to relocate the motor control (control signals, firmware, and power supply conditioning) from a centralized box to each motor. From an external hardware perspective, I want to replace the central control box and multiple cable schemes with a single cable.

    (see image titled “proposed_3_axis_design.PNG”)


    What type of cable to use?
    A USB-A cable (5 ampere rated) should work for a NEMA-23 motor. I do not want to use USB signals, just the USB-A cable design. A HVAC cable should work for a for NEMA 34 motors. HVAC cables have monstrously large amperage ratings. Both USB cables and HVAC cables have provisions for power and one “LVDS” (digital) signal pair.( half-duplex)

    Which type of cable will not work:
    An “Ethernet” cable design is not viable due to amperage requirements of “NEMA 23” and/or “NEMA 34” motors. Ethernet cables are designed to propagate high speed AC signals not convey large currents.




    The basic benefit(s) for the end customer:

    1. Vastly simplified motor connection(s). Power and control are combined in single cable. No central box with multiple cables.
    2. Simple MODBUS type expansion upto 128 control nodes (motors, end stops, probes, coolant jets, ect). Just configure one 7 bit DIP switch for each control node with a small screw driver.


    (see image titled “DIP_switch.PNG”)


    1. Cheap, ubiquitous, commercially available replacement parts. (USB cables, HVAC cables, USB to RS485 converters, power supply)

    Basic questions for CNC zone readers:
    Does the above described product exist on the market?
    Do the above benefits sound appealing?
    If this is a good idea, then which motor should I develop first “NEMA 23” or “NEMA 34”?
    Is the smaller NEMA 23 motor relegated to “niche” hobby markets?


    Please share your constructive thoughts with me.
    If you know of a forum better than CNCzone , then please tell me.
    Attached Thumbnails Attached Thumbnails proposed_3_axis_design.jpg   DIP_switch.jpg  

  2. #2
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    118

    Re: Motor_Controller_Design

    A USB-A cable is rated 5 ampere at 5 volt over a short distance and is not decently shielded.

  3. #3
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    Aug 2015
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    Smile Re: Motor_Controller_Design

    Quote Originally Posted by klaas123 View Post
    A USB-A cable is rated 5 ampere at 5 volt over a short distance and is not decently shielded.
    I thank you for your time write a reply!

    The dielectric of a standard USB-A cable is rated at 20V. I am guessing that a 20V dielectric will endure up to 50V. In general amperage is the conductor killer, not voltage. So say that the power supply is 48V, the current is 5A.

    The maximum continuous power applied to a NEMA 23 motor would be:

    P= V * I = (48V)*(5A)=240W

    I am guessing that a 240W power supply is enough for a NEMA 23 motor. (someone please correct me)

    Mechanical engineers use strange units (oz-in) (N-m). A better unit would be (Joules)/(cycle). "(Joules)/(cycle)" would allow direct translation of a motor's power requirement for a given rotation rate(Hz).


    Also the digital signals inside of a USB cable are differential. A "differential" digital signal design is specifically used to eliminate the corrosive effects from noise from adjacent unshielded power conductors. The low frequency AC transients from power supply are not a problem worth losing sleep.

    I again thank you for your reply!

    PS. Holland should declare the "Stroop Waffel" the national cookie! "Stroop Waffel" => YUM!

  4. #4
    Community Moderator Al_The_Man's Avatar
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    23563

    Re: Motor_Controller_Design

    I really don't see the advantage?
    setting up remote controllers for each motor, you will still need interpolation commands sent from some source or another.
    Also, NEMA is not a motor power rating, it is a mounting plate standard.
    You can obtain commercial stepper motors where one is double the length of another, i,e, power x2 but still have identical NEMA mountings.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  5. #5
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    Aug 2015
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    6

    Re: Motor_Controller_Design

    Al ( Boomhauer?),
    I thank you for your reply!

    What I would like to develop is >90% hardware. Any modifications interpolation software(and firmware) from existing application software will as small as possible. For example, I do not want to develop a new “g-code” interpreter.

    Ideally, I want to deliver to the end user a product that has:

    1. Other than motor itself use universally available off the self parts E.G. USB-A cables, cheap ubiquitous 48V power supplies, HVAC cables, USB to RS485 dongles.
    2. Chimp simple “Product commissioning” . “Product commissioning” are the steps between connecting cables and power to your product and when the software communicates to hardware.
    3. Eliminate the central box and separate motor controllers (IE Gecko controllers)
    4. Vastly simplified product connections


    I will grant you challenges exist!
    The biggest challenge is motor synchronization to less than say 0.1 millisecond. The synchronization challenge has been solved for Ethernet, so I do not foresee and “deal killers” in terms of firmware development with a RS485 interface.

    Basic product commissioning would the same as has been done in the HVAC industry for the last 25 years.
    STEP 1: RS485 interface initialization.
    STEP 2: Control node initialization.
    Explanation STEP:1
    An RS485 interface mimics the RS232 firmware/software interface that already exists on your computer’s operating system. Some RS485 devices are “plug and play”. You only need to transfer the COM port number (EG 2,6,12,31) to your application software.
    Example RS485 device:
    https://www.ftdichip.com/Products/Cables/USBRS485.htm
    Explanation STEP:2
    By “control node” I mean something like a end stop detector, motor, coolant sprayer, fan, end mill dust vacuum. In the HVAC industry, control nodes have “DIP_switches”. A small jeweler’s screw driver adjusts the switches. Control node commissioning is done by generating a 7 bit number with the DIP_switch for up to 128 control nodes. The bus then recognizes each control node by unique ID number. No additional hardware initialization necessary.

    (Please see attached image “DIP_switch.PNG”)

    As far as the definitions of NEMA 23 and NEMA 34, please forgive me. I am an EE not ME. Please forgive me!
    Please look at the two data sheet snippets for NEMA 23 and NEMA34 motors. Do the performance numbers suggest a stout motor suitable for say a NEMA 23 or a NEMA 34 3-axis gantry mill?

    Please see attached image “Example_NEMA_23_specifications”
    Please see attached image “Example_NEMA_34_specifications”

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