Thread: "DeusEx"

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  1. #11
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 19 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    The main benefit of Gecko's is the microstep to full step morphing, plus they're small!

    I've got 2 G251s in my lathe, and can't fault them.
    I did think about getting the G540, but it wouldn't of fitted in the control housing, and I already had the SmoothStepper and C23 break out board so didn't really need any of the additional features of the G540. If I was to start from scratch, I probably would go for the G540, as it does most things you need (inputs/outputs/0-10V speed control) in one plug and play package. Just add power, a parallel cable, some steppers and resistors, and you're good to go.
    If you do still consider the G540, look at the GC-02 and GC-04 connectors from www.homanndesigns.com, as they make wiring even simpler!
    Also, the Gecko customer appreciation sale must be about due, so if you're not in any hurry, keep an eye out to get the drives even cheaper than what the UK importer charges

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  3. #12
    Thanks guys!

    I'm just reading about the 540's and doing a side by side with the Kinco 2M880N (that was top of my list...)

    I don't know what "microstep to full step morphing" is, or if there is any advantage of "256 microsteps", my reading list just got a bit longer!
    :-)

  4. #13
    Quote Originally Posted by mocha View Post
    I don't know what "microstep to full step morphing" is, or if there is any advantage of "256 microsteps", my reading list just got a bit longer!
    :-)
    The morphing thing is, from memory, switching to full step mode when the motor is run at higher speed. It's a good plan as you get a bit less torque when microstepping...
    I wonder if the gecko's use vector current control, like the 2M880N, bet they don't...could be wrong.

    To me it's obvious - get the 2m880N as that's about 50% higher voltage than the gecko which should have a much greater affect than the rest of it.

    No point in using 256 microsteps ... that high wont help with accuracy (only cheating yourself if you think the resolution is 256th of full step resolution). As long as the driver does up to about 10 microsteps that's fine.

    More info on microstepping here, here and here:

    http://www.micromo.com/microstepping...realities.aspx
    http://www.euclidres.com/apps/steppe...r/stepper.html
    http://reviews.ebay.com/Microsteppin...00000002352664

    Disclaimer :
    Other websites are available ...
    Your blood pressure can go down as well as up if you choose to read them ...
    Last edited by Jonathan; 19-09-2011 at 10:41 PM. Reason: Numerous

  5. #14
    Thanks Jonathan, lol, I got as far as "Magnetic backlash" and decided I need far more coffee than I've had already! I'll leave it for tomorrow! :-)

  6. #15
    Quote Originally Posted by Jonathan View Post
    I wonder if the gecko's use vector current control, like the 2M880N, bet they don't...could be wrong.
    If by vector control you mean current recirculation while stood still then yes they do.

    Quote Originally Posted by Jonathan View Post
    To me it's obvious - get the 2m880N as that's about 50% higher voltage than the gecko which should have a much greater affect than the rest of it.
    Only really apply's if your motors are good for the extra voltage.? Most nema 23's are not when wired parallel.!! . . . . Over rating a motors voltage will give extra speed but it also creates extra heat, iron loses etc which then slowly damages the motor shortening strength and life.

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  8. #16
    Quote Originally Posted by JAZZCNC View Post
    If by vector control you mean current recirculation while stood still then yes they do.
    No, I mean vector control. I wont try and explain as it's a tricky one:

    http://en.wikipedia.org/wiki/Vector_control_(motor)

    http://www.eng-tips.com/faqs.cfm?fid=1062

    Quote Originally Posted by JAZZCNC View Post
    Only really apply's if your motors are good for the extra voltage.? Most nema 23's are not when wired parallel.!! . . . . Over rating a motors voltage will give extra speed but it also creates extra heat, iron loses etc which then slowly damages the motor shortening strength and life.
    Mocha is using the same motors as I am, or at least very similar - 3Nm Nema 23 with low inductance. I've been running mine on 75V since I got them well over a year ago with no ill effects. The highest temperature I have ever recorded was 60 celcius (so at least 25C below rated) on the case which was on a sunny day when the machine had been running for a couple of hours. Most of the time they linger around 45C. I check it regularly as I have an infra-red thermometer to hand and it's something to do whilst the machine's running...good for getting estimate of cutter temperature too.

  9. #17
    Quote Originally Posted by m_c View Post
    The main benefit of Gecko's is the microstep to full step morphing, plus they're small!

    Thanks, m_c, I'll face the rigours of JB's reading list in the morning! I'd seen the Homann site, it was very helpful and the ease of installation of the 540 is a bonus although sorting the electricals doesn't concern me as much as some of the other decisions! (It's just like wiring a plug, lots of plugs! )

    I'll certainly keep an eye open for the sale! Thanks for your help!

  10. #18
    Quote Originally Posted by Jonathan View Post
    No, I mean vector control. I wont try and explain as it's a tricky one:
    No need to explain I know all about torque vecter drives but are you sure these drives mean the same.? I don't see any referance to torque vector control but I do see current limiting (Half current).?

    Quote Originally Posted by Jonathan View Post
    Mocha is using the same motors as I am, or at least very similar - 3Nm Nema 23 with low inductance.
    If these are the motors with 3mh inductance I've seen specs sheets flouting around for then your running them approx 20V over spec, this will sooner or later have an affect.!!

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  12. #19
    I'll compare with PM752 driver as that's what I have. Copied from Gecko site:

    3.5A 50VDC maximum PM752, 75V & greater current
    Digitally filtered STEP, DIRECTION and DISABLE inputs same
    3.3V and 5V logic compatible inputs Same I think, can go higher with resistor. Also if you accidently pop one with 75V it's easy to replace the optoisolator :naughty:
    300 kHz maximum step pulse frequency same, but who needs more than about 50kHz anyway
    Top settable Adjust trimpot None
    Power LED indicator same
    No user settable jumpers PM752 has internal jumpers for motor direction and something else I can't remember ... not much use really
    20 kHz switching frequency I'm pretty sure PM752 is much higher, will check it with scope tomorrow
    Mid-band resonance compensated Probably none
    Microstep to full step morphing at higher speeds Probably none
    Small size Nobody cares
    Four layer PCB That just means they weren't good enough to make it 2-layer
    Discrete all N-channel MOSFET full bridge design same
    14A rated power MOSFETs PM752 mosfets are 33A and 100V, so will almost certainly have lower Rds and therefore power dissipation.
    3.5mm 12 position connector with screw type terminal Pluggable, which in my opinion is better
    Recirculate mode while the motor is stopped, reducing motor heating Probably none
    70% current when stationary 50% on PM752 so possibly lower power dissipation - possibly not due to the above, can be changed with a bit of effort

    Maybe I should have compared with a different Gecko, but you get the idea.

    One more for your reading list:

    http://www.scribd.com/doc/29405701/C...osition-Sensor

    Looks like vector control is one up from resonance damping.
    Last edited by Jonathan; 20-09-2011 at 12:42 AM.

  13. #20
    Quote Originally Posted by JAZZCNC View Post
    No need to explain I know all about torque vecter drives but are you sure these drives mean the same.? I don't see any referance to torque vector control but I do see current limiting (Half current).?
    http://www.zappautomation.co.uk/prod...ec77476e499bf4

    'The application of advanced vector control algorithm greatly reduces noise and vibration of the motors during operation, '

    The link I gave in my previous post explains it better. In particular this is interesting:

    'The motor operates in continuous mode rather than conventional stepping mode.The audible
    noise and resonance effects associated with conventional stepping mode are effectively
    eliminated.'

    That sounds alike to the Gecko - although it's not full stepping at higher speeds it's applying a sine wave to each phase, so operating it like a 'normal' motor not stepper motor. Bound to be quieter and more efficient for obvious reasons.

    I'm intending to implement vector control on the stepper driver I'm designing/prototyping.

    Quote Originally Posted by JAZZCNC View Post
    If these are the motors with 3mh inductance I've seen specs sheets flouting around for then your running them approx 20V over spec, this will sooner or later have an affect.!!
    Well it's been 16 months. I'll let you know if they break!
    The formula you are probably using to say they are 20V over-spec (32*sqrt(L)) is almost certainly an oversimplification / guideline. I think the fact my real life experience with these motors shows the temperature is fine at 75V says it all.
    Last edited by Jonathan; 20-09-2011 at 12:54 AM.

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