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IndustryArena Forum > CNC Electronics > Stepper Motors / Drives > L6474 or powerStep01 drivers
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  1. #13
    Company Representative
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    Feb 2007
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    942

    Re: L6474 or powerStep01 drivers

    Thanks
    Here is my little 4 axis motherboard with plugable L6474 toasters.
    The problem is probably the mosfets in the output bridge don't have a low enough on resistance .

    The other thing i don't like is having to send serial data every time just to change the current when the motor is idling. This is prone to eventually glitching with the wrong current value and will cause the motor to stall.
    They should have a separate line for 2 banks of settings.

    Larry
    Attached Thumbnails Attached Thumbnails IMG_5765.jpg  
    Manufacturer of CNC routers and Viper Servo Drives
    www.LarkenCNC.com and www.Viperservo.com

  2. #14
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    Jun 2012
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    113

    Re: L6474 or powerStep01 drivers

    Yes, I suspect you are correct about the output FETs but switching timings can affect heat produced since switching too often means more transient time when you are not even in the 'on resistance' mode of the FETs.

    I used much smaller heat sinks than you have. IIRC they were pulled off a DRAM memory card and were lightly finnned about the size of a 20 pin DIL. I think the spec for the copper cladding described for PCB design was too light.Also some forced ventilation is needed for continuous operation.

    Why do you need to change the current when the motor is running ? Why does this cause glitches ? I managed to send a 3 byte command to a stack of three driver boards in 20 us on an arduino uno. That should be able to fit into any machining pulse timing without causing a fault. How fast are you running the steppers? Disable interrupts and bitbang the SPI and you can get back out before anyone notices

    What software are you running? I use modified GRBL, anything using Arduino libs will be a disaster.( I dropped Atmel hardware anyway and use STM now )

    [EDIT] I had a quick look at your site products but does not seem to be what you are discussing above. Are you still using a printer port of a Windows PC for stepper control ?!

  3. #15
    Company Representative
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    Feb 2007
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    942

    Re: L6474 or powerStep01 drivers

    The spi update is to set the 50% idle current when the motor sits or more than a second. But repeated sending serial with no error correction could eventualy lead to an error in a noisy environment.
    I have an onboard pic that sends the spi commands . The drive just accepts step/dir .

    ( I'm using it on my small cnc routers running my starcnc usb controller. I don't sell it separately. )

    On your powerStep01 , having to send an spi to change the direction is pretty crazy. Those chip designers seem out of touch with the customers. Step/dir is the standard interface for 30 years.

    Larry
    Manufacturer of CNC routers and Viper Servo Drives
    www.LarkenCNC.com and www.Viperservo.com

  4. #16
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    Jun 2012
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    113

    Re: L6474 or powerStep01 drivers

    I agree that not having a dir pin seems odd. Not sure what the motivation for that was. They seem to regard the whole step/dir paradigm as "legacy" and intend the use of the on chip motion control. These chips are probably aimed at automotive applications rather than machine control.

    Since dir can only change at min step speeds, it's not much of an issue thought. Likewise for setting idle current. If you can not ensure enough noise immunity you will have problems at some point, you could equally get false step pulses or unexpected change of direction for a couple of steps.

    If the error results in a bad command, there is an error code and the FLAG pin trips. If you need to double check, you could always read back any param settings via SPI to ensure that they return the value which was sent.

    With proper shielding and circuit layout it should be possible to make such comms to work perfectly over the very short distances involved.

  5. #17
    Junior Member
    Join Date
    Jun 2010
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    3914

    Re: L6474 or powerStep01 drivers

    They seem to regard the whole step/dir paradigm as "legacy" and intend the use of the on chip motion control.
    They have made the wrong choice in the wrong market but do not want to acknowledge that. Referring to 'Step/Dir' as 'legacy' can only be described as hilariously ignorant (or commercially biased). And I strongly doubt the auto industry will go for any unique orphan custom variation.

    When you come across a vendor like that, the best thing you can do is to simply write off any investment you have made and walk away. Trying to recover any sunk costs is just utterly futile.

    Cheers
    Roger

  6. #18
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    Re: L6474 or powerStep01 drivers

    "hilariously ignorant (or commercially biased)"

    Well it would be fair to assume that STM makes "commercially biased" decisions and are not "hilariously ignorant". It should be underlined that it was only my guess that is what they are doing with these chips. There probably is a market for small compact chips with enough intelligence to provide "goto X" with preprogrammed accel params, without the need for external step by step control. Window winders springs to mind. In an automotice context I would not want to tie up CPU time servicing every single pulse of a window motor movement.

    This paradigm does not suit all uses so they retain the alternative STEP input as well.

    Some of the advanced current control methods are only available using the internal motion control, which is unfortunate for my needs but probably a necessary limitation rather than hilarious ignorance.

    They may not be ideally designed for CNC control but for the minor inconvenience of sending a SPI sequence to set DIR they do seem to provide good voltage and current capabilities and with a demo board costing about $15 per motor they are a snip compared to other options.

    It is amusing how small business niche users are willing to call global corps "out of touch" or "hilariously ignorant". Maybe you are not part of their target market for this product.

    [ PS This relates to the PowerSTEP01 , not the L6474 titled in this thread. The former does not have heat problems mentioned. Both STM chips and very similar in operation and control .]

  7. #19
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    Re: L6474 or powerStep01 drivers

    Window winders springs to mind.
    Very good point. The world does not revolve around hobbyist CNCs.

    Cheers
    Roger

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