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  1. #1
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    Default Confused.

    I have a Chinese cnc that I have retrofitted with a set of motors, cables, and G540. I had a hobby cnc controller on it, and with that setup I could get about 30in/min. When I upgraded to the G540 I thought I would get higher speeds. I can get the same 30 in/min but when I move up speeds I get motors stalling (like really whining not just loss of power). It is random. I can physically push against the gantry with all my weight at 30 in/min and it will not stop. But if I bump speeds unto 40in/min it randomly stalls.

    I have mach3 and have tried just about everything I can find online. Does anybody have suggestions?

    Thanks

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    Default Re: Confused.

    I tried just about everything, and am trying a complete reformat of the computer. Then I will reinstall software, reset everything, and if I still can't get it to work I am putting my old "made it myself" hobby cnc that worked just as well as this. I wish I had never bought the gecko at this point. I don't have a scope to check the gecko. I checked pin outputs on both the computer and the drive end of the cable. Power supply is putting out the correct power.



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    Default Re: Confused.

    Do you have a big enough PS for motors?
    https://www.cnczone.com/forums/gecko...er-supply.html



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    Default Re: Confused.

    I bought the g540, power supply, motors, cables, vfd, and spindle setup from a seller that has done a lot of these setups. It should be but, I am going to check the power supply while the machine is running. I am going to see what the voltage output is when the stall happens. I am going with a freshly restored computer with fresh software install. I don't have another computer with a parallel port that I could switch out. I keep coming back to the computer or the gecko, but have not ruled out the power supply while under load.


    I even went as far as to measure the resistance of the gantry and carriage without being connected to the ball screws. It measures around 4# to initiate movement and around 1.8# to keep movement. There is a little resistance, but I believe that is because of the wipers on the rails. I am going to setup a test for the ball screws today and see if there is some loss there. I held the ballscrew and cycled through the length and did not feel anything.



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    Default Re: Confused.

    Sorry to hear about your trouble. I had a G540 and found it to be reasonably good. Did you "select" the correct amperage for your motors?



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    Default Re: Confused.

    Yes, I used the resistors that were provided with the package I bought.

    However, when trying to reformat the computer something glitched, and of course windows 7 is no longer supported. I have my dell service number tag as well as the windows serial number tag but can't get a download in order to reinstall the OS I am probably going to shelve the whole thing until I can afford to buy an eternal adapter and a computer that will work with it. My only other computer is a mac, so its no help.



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    Default Re: Confused.

    Hi,
    what are the spec of the steppers? I suspect they are high inductance types.

    ALL steppers lose torque the faster they go. A 23 size stepper of 1mH inductance (very good spec) will have about 40% of its torque at 1000rpm whereas a 23 size
    stepper of 8mH (vey average spec) inductance will be lucky to have 5% of its torque at 1000rpm and will more likely have stalled at 350rpm say.

    The bottom line is that low inductance steppers are required for CNC axis motors for which you want high speeds.

    Stepper manufactures know that first time buyers don't know about inductance so they make (cheap) high torque motors but with an unacceptably high inductance.....
    and lack of speed results.

    The classic way to overcome stepper inductance is to use the highest voltage driver and power supply you can get your hands on. The Gecko 540 is rated to 50V, which is
    not bad, but not earth shattering. The G540's bigger brothers are 80V capable. My Vexta 5 phase stepper drivers are over 150V!!!

    To make your machine run as fast as it can use a 48V or 50V supply with your G540. Note that the G540 is a quality brand and while it may not solve the lack of speed issue for you
    it will work as advertised.....much better than the stuff the Chinese commonly sell.

    If you want your machine to really sing you need low inductance steppers. In 23 size 1mH to 2mH, 1 mH preferred and REJECT anything over 2mH.

    You may see a lot of hype about 'closed loop steppers', it's just that......hype. While there are some advantages to closed loop operation they are are not enough to justify the expense.
    The manufacturers claim they go faster...they don't. They do use low inductance motors and that allows them to go fast....if you used low inductance steppers you could go fast too,
    open loop.

    Low inductance steppers tend to have high current ratings. To get low inductance you need fewer turns on the coils, but to obtain maximum torque the current must be higher
    because of the fewer turns. Inductance is inversely proportional to the square of the turns whereas the torque is proportional to turns, thus you can get a better performance
    from fewer turns, at the expense of the cost of the wire.

    Often a motor of somewhat lesser torque but also much lower inductance will prove to be better for CNC axis motors than a higher torque motor of exactly the same size
    because it has higher inductance.

    Craig



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    Default Re: Confused.

    Hi,
    I ran Mach3 on a parallel port for a couple of years without problems, and at what I thought was pretty good speeds.
    Then I bought an Ethernet SmoothStepper (genuine Warp9TD, not a Chinese fake) and I found that I was able to go 33% faster, still without losing steps,
    and the motors 'sound sweeter' and run a little more coolly. I did not think an external motion controller would make that much of a difference....but it did.
    With an external controller I can run Mach on just about any PC I like and can junk the old 32bit XP and 32bit Windows7 clunkers that I used to have to
    use before.

    Craig



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    Default Re: Confused.

    Hi Svon - what was the voltage of the old setup? Was it more then 50V? this maybe the simple answer. Plus the G540 uses resistors to limit current. have you current matched the motors or just used the resistors that came with it? I say this because the resistors you have maybe limiting current too far. So check those out. The correct values are in the docs. I do recommend an external motion controller. smooth stepper, UC100 etc then the computer is not as important. Cheers Peter



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