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  1. #1
    I've got a Bridgeport Series 1 CNC with shot 3 phase electrics. I've come to the conclusion it's best to give up the original motors and go for new steppers and a complete rewire etc. I've trawled the forums for hours trying to educate myself but I'm still not exactly sure what I need. Something like this kit from Longs (https://www.ebay.co.uk/itm/EU-Free-S...4AAOSwMPxbkIMJ) which includes motors, power supplies, BOB and drivers. Longs offer different versions of NEMA34 and NEMA42. Does anyone here have experience with how many oz-in are required to power the XYZ axes on a BP Series 1? I was thinking maybe the Nema34 1200 oz-in would work but I'm really not sure?

    I'm on a budget so a servo motor conversion is out of my reach, hence the interest in these relatively inexpensive Chinese kits. Thanks in advance for any advice or links you can point me to.

  2. #2
    I don't know what torque you need to move the Bridgeport but

    looking at the kit you linked to

    the motors 8mH inductance is too high when using the 60V power supply supplied

    you either need to have a motor inductance about 3.5mH to use the 60V supply or
    stepper drivers that will work with a 90V power supply if you use the 8mH motors

    I would use another breakout board that does not have opto-isolators on the outputs connected to the stepper drivers

    connecting the KITs BOB to stepper drivers with opto-isolated inputs will degrade the sharp edges of the step pulses

    John

  3. #3
    Thanks for the info John. I need to do some homework so I can get my head around the relationship between mH and volts!

  4. #4
    a rule of thumb from Geckodrive .com is the supply voltage to the driver is
    32 times the square root of the motors inductance in milli henry

    the higher the inductance the greater the voltage needed to ensure the current builds up to the desired current in limited time between step pulses

    John

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  6. #5
    Quote Originally Posted by john swift View Post
    you either need to have a motor inductance about 3.5mH to use the 60V supply or
    stepper drivers that will work with a 90V power supply if you use the 8mH motors

    John
    Investigating further, their NEMA34 1100 oz-in motors have 3.5mH inductance.

    https://www.ebay.co.uk/itm/Free-Ship...UAAOSwy6lbkJ1q

    But does that combo have sufficient torque for a Bridgeport...?

  7. #6
    Quote Originally Posted by john swift View Post
    I don't know what torque you need to move the Bridgeport but

    looking at the kit you linked to

    the motors 8mH inductance is too high when using the 60V power supply supplied

    you either need to have a motor inductance about 3.5mH to use the 60V supply or
    stepper drivers that will work with a 90V power supply if you use the 8mH motors

    I would use another breakout board that does not have opto-isolators on the outputs connected to the stepper drivers

    connecting the KITs BOB to stepper drivers with opto-isolated inputs will degrade the sharp edges of the step pulses

    John
    I am obliged for this answer as I have a Longs 3 axis kit for my tiny hobby router.I was hugely pleased just to get it moving and anticipate a series of upgrades.I liked the idea of opto-isolators as it appeared to make it less likely that the magic smoke would escape;I had no idea there was a performance penalty.Can anybody suggest what might be an improvement?I am currently using on old Dell with a parallel port and wouldn't mind a more modern type of connection.I hope the OP won't mind me asking as I believe he might also benefit from an answer.

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  9. #7
    with stepper drivers like the dm860a that has its own input opto-isolators
    Click image for larger version. 

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    you don't need a breakout board with output opto-isolators like this supplied in the kit-
    Click image for larger version. 

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    these two BOB's only buffer the printer port outputs and only opto-isolate the 5 inputs -

    a breakout board like this found in some of the ready made control boxes
    Click image for larger version. 

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    the closest available on ebay is something like this
    Click image for larger version. 

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    note it does not have the 5V DC/DC converter found on the TX14175 and requires another power supply

    the least expensive change will be the breakout board but it may not make any noticeable
    difference when using the original motors and drivers


    As I don't have the longs kit to test, I don't have a definitive answer but
    problems the original breakout board will only show up at high speeds
    the original motor / driver combination may limit the maximum motor speed first

    without going through all the stepper motors , stepper drivers and power supplies on sale

    its not easy to say which is the most cost effective change

    using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

    John
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by john swift; 01-11-2018 at 11:56 PM.

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  11. #8
    Quote Originally Posted by john swift View Post
    As I don't have the longs kit to test, I don't have a definitive answer but
    problems the original breakout board will only show up at high speeds
    the original motor / driver combination may limit the maximum motor speed first
    without going through all the stepper motors , stepper drivers and power supplies on sale
    its not easy to say which is the most cost effective change
    using a higher voltage supply & stepper drivers verses replacing the motors with lower inductance motors

    John
    A very informative and educational reply! Allows me to analyse motor and driver specs with a little more knowledge than I had yesterday. Thanks for taking time to explain things in such detail.

  12. #9
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Days 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 2,908. Received thanks 360 times, giving thanks to others 8 times.
    It's worth highlighting the main reason opto-isolators are added to BOBs is for protection.
    Using a parallel port, get something wired wrong, or have something short and connect power to pins they can't withstand, then more than likely your PCs parallel port (and likely entire motherboard) will be dead.

    With newer motion controllers, the path of destruction from a wiring problem isn't likely to be as long, but it's still potentially a couple hundred pound controller that could be releasing it's magic smoke.

    It's a calculated risk not using them, but at slow speeds, they shouldn't cause any problems. I certainly wouldn't be searching out a BOB without them, unless I was really going to be pushing pulse rates.


    Regarding suitable motors.
    A good starting point would be to try and find out the torque for the existing motors, or even a datasheet with torque curve (it's surprising what a google for the model number turns up).
    You can then run a few figures and see how the various options compare. You'll likely find some suitably geared NEMA23/4s provide better performance than NEMA34s directly coupled, especially when running from lower voltage.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  13. #10
    I would Not retrofit a precision metal cutting machine with an Open Loop system , given prices of new cheap servo motors and drives, used servo motors and drives and closed looped steppers which i dont like much pricewise
    project 1 , 2, Dust Shoe ...

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