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  1. #801
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    Jan 2005
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    31
    I GOT MY MINI-G's !!!!! They are very cool. I plan to try a couple of them out tomorrow on a old t-tech table. Of course the wife snagged the cute little silver/purple gecko that came with it, but thats ok with me. Thank you so much for running the contest. Now I only need to buy one more to have 2 machines up and running. The T-tech uses a solenoid for z axis.
    I have followed this thread since day one and all I can say is you guys are brilliant. And some of the friendliest folks who make stuff for sale I have ever seen.
    PS This is not trying to butter you up as I already won. Just a statement of fact.
    klmjr

  2. #802
    Gold Member
    Join Date
    Apr 2006
    Posts
    3488
    hmm....When i saw the picture of drive on match box...I flabbergasted to see the tiny lizard...it was amazing....How these tiny drive can run the big machines...i thought....

  3. #803
    Hi. Here's what I working on today.
    I made it in DipTrace, and it's free to use.
    (Size 107.50mm x 76.25mm.)
    Attached Thumbnails Attached Thumbnails G251_Schematic.jpg   G251_Silk.jpg   G251_Top.jpg   G251_Bottom.jpg  


  4. #804
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    May 2008
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    12

    G540 Status

    So when can we expect to see the G540 available?

  5. #805
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    Jan 2007
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    twit,

    The G540 should be available some time soon, hopefully in the next month and a half to two months. We still need to finish prototype testing of the updated version. I ordered the G540 cases yesterday, and we should receive those in about three weeks. I am hoping to get the G540 PCBs some time around then as well, but it all really depends on how testing goes. I don't see why it would not go well, but I prefer to err on the side of caution and say that it will be available in early July.

    -Marcus Freimanis

  6. #806
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    May 2008
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    12

    Re G540

    Thanks, CoMarcus

    When the G540's become available will it be possible to purchase it without the internal G250s? I'd like to get my hands on a set of G250s as soon as they come out but may not if I'm required to buy another set with the G540...

    Also noticed on the G540 Schematic dated March 2, 2008 -- no pullup Rs on the ILQ74 for DB25 P11-P13, P15? Has this been fixed or are pullups on the PC side?

    Lastly, will the parallel interface port be male or female? I've seen both on some of your prior posts.

    --Twit

  7. #807
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    Aug 2005
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    895
    Where would you like them pulled up to?

    There are no pullups as it is on the isolated side of the G540. Pulling them up to the voltage rails on the G540 would negate the optoisolation. The pull ups will need to be on whatever circuitry (breakout board etc) that the outputs are connected to.

    Cheers,

    Peter.



    Quote Originally Posted by twit_biddler View Post
    Thanks, CoMarcus

    When the G540's become available will it be possible to purchase it without the internal G250s? I'd like to get my hands on a set of G250s as soon as they come out but may not if I'm required to buy another set with the G540...

    Also noticed on the G540 Schematic dated March 2, 2008 -- no pullup Rs on the ILQ74 for DB25 P11-P13, P15? Has this been fixed or are pullups on the PC side?

    Lastly, will the parallel interface port be male or female? I've seen both on some of your prior posts.

    --Twit
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  8. #808
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    May 2008
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    12
    Quote Originally Posted by phomann View Post
    Where would you like them pulled up to?

    There are no pullups as it is on the isolated side of the G540. Pulling them up to the voltage rails on the G540 would negate the optoisolation. The pull ups will need to be on whatever circuitry (breakout board etc) that the outputs are connected to.

    Cheers,

    Peter.
    I'd like them pulled up to a TTL compatible isolated supply of course. My money is on the parallel port interface already having them though -- It'd be a bit of a kludge to have to also include a breakout board to interface something as fundamental as limit switches or axis zero point switches to the computer.

    Be kind. I'm kinda new to this...
    -- Twit

  9. #809
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    Feb 2008
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    241
    Here's an update on the G251 testing. I added a third G251 to the small case that I had the other two mounted in and after talking with mariss found out that there is a mid band stabilization trim pot that I wasn't aware of. This came up as a result of me mentioning that the G251 was very comparable to the G203 when you run the slow increase in acceleration. I mentioned that is was good but not quite as good as the G203. He asked me if I had adjusted the trim pot on the G251 and after looking at it said "NoI hadn't". I then went back adjusted the very tiny trim pot and sure enough the motors ran even smoother. The only thing that is critical is that you need a very small screwdriver to adjust the trim pot. If you try using a large screw driver you could possibly short out the adjacent components. I would recommend using a toothpick with the end shaped like a flat bladed screw driver to avoid that disaster.
    Running three axis using 632 oz in steppers for several hours was no problem. While I have afan mounted inside the case it really isn't necessary. I just out of habit built up a box that had a fan mount already in it.
    Looking great!

  10. #810
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    466
    Quote Originally Posted by twit_biddler View Post
    Thanks, CoMarcus

    When the G540's become available will it be possible to purchase it without the internal G250s? I'd like to get my hands on a set of G250s as soon as they come out but may not if I'm required to buy another set with the G540...

    Also noticed on the G540 Schematic dated March 2, 2008 -- no pullup Rs on the ILQ74 for DB25 P11-P13, P15? Has this been fixed or are pullups on the PC side?

    Lastly, will the parallel interface port be male or female? I've seen both on some of your prior posts.

    --Twit
    Twit,

    The G540 will only come with drives already installed. The G540 will only be available in the four axis configuration (or 1 axis with 3 spares ;-) ), and they will be sent out all exactly the same. This makes our life easier and allows us to produce them very quickly if they are all the same.

    The DB9 and DB25 connectors will be female connectors to avoid contamination on our end.

    The pullup resistors are on the board, but got left out of the schematic. Whoops!

    Like Dan said, the trimpot is very small. It must be adjusted with caution because it is so small, and a small flat blade will be your best bet.

    Some of you may find this interesting, so I will post it. Last week I ran a heating test on the G250 with kapton tape on the MOSFETs and screwed down to a heatsink. This is because the MOSFETs are not isolated, and if someone were to screw them down to a non-hard anodized aluminum plate that would be the end of the drive. I wanted to see how the kapton tape acted in place of the heatsink compound, and the results were very impressive.

    The first number is time, then MOSFET temperature, then plate temperature.

    Start, 57C, 52C

    5 min, 65.9C, 59C

    10 min, 68.7C, 65.1C

    15 min, 72C, 61.6C

    20 min, 74.2C, 65C

    25 min, 71.3C, 64.2C

    As you can see, the temperature of the MOSFETs and the plate was less than 10C difference, which means that the heat was in fact being distributed to the plate. Because of this, all G250s will come with double sided kapton tape on the MOSFETs. When you receive them, all you have to do is peel off the plastic covering the other sticky side and screw it down to your heatsink plate if you use one.

    Marcus Freimanis

  11. #811
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    Apr 2004
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    99
    I just got my two G-Mini today, they are really cute and beautiful. Thank's to all the people at GeckoDrive.

    -ichan

    Q: Why the size of the heatsink plate is smaller than the size of the board?

  12. #812
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    Ichan,

    The heatsink plate is smaller than the board because of a stupid mistake on our part. It will be fixed once all these plates are used up, but it affects nothing but aesthetics.

    Marcus Freimanis

  13. #813
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    Quote Originally Posted by CoAMarcus View Post
    As you can see, the temperature of the MOSFETs and the plate was less than 10C difference, which means that the heat was in fact being distributed to the plate. Because of this, all G250s will come with double sided kapton tape on the MOSFETs. When you receive them, all you have to do is peel off the plastic covering the other sticky side and screw it down to your heatsink plate if you use one.

    Marcus Freimanis
    It just keeps getting better!

    Thanks Marcus!

    CR.

  14. #814
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    Jan 2008
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    31

    power supply current rating?

    Quote Originally Posted by CoAMarcus View Post
    Mongkol,
    Regarding the voltage to feed your drive, this is dependent on the inductance of your motor. Below is the correct and most up to date formula for figuring out the proper supply voltage:

    Drive supply voltage = 32 * SQRT(mH inductance)

    If your motor is rated at 4mH, then it will be 32 times 2, or 64VDC.

    Your motor will be way too high inductance to use with our drives, as the voltage required to push the current through the windings to compensate for iron losses will just be too high.

    -Marcus Freimanis
    From the statement above am I correct that 3.8mH for 62VDC will be too high as well for this drive? Was going to buy these cheap steppers but after reading this I checked and they are 3.8mH so not useful with the G250. I do have some lower torque steppers which I'll try out first that are 3A, 2.2mH which works out just right at 48VDC.

    I discovered this searching for info on the correct current rating for the power supply I need to buy. The only thing that has me confused is the fact that the motor rating is 3A/phase. Does this mean for one motor I need a 6Amp supply (2 phases x 3Amps) or a 3Amp (only one phase firing at a time) power supply?

    I've also been thinking about the inductance looking at stepper motor specs and as I suspected, the inductance goes up, current rating is down (more copper windings so this is expected) and visa versa (less windings, lower inductance, higher current). From what I can see this means the ideal maximum torque stepper motor for the G250 is about 200oz-in, maybe a bit more. Motors above this will not run to their full capability due to reduced drive voltage or and current. So if I want to run higher torque steppers at their full capacity I should be looking at the next model up Gecko drive such as the G201, correct? Or am I looking at this the wrong way and the G250 will drive any 3Amp stepper to it's best (I suspect not but I'm not qualified in this area to confirm).

    Thanks
    Steve

  15. #815
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    Apr 2008
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    1
    I've been following this thread with great interest for a while, as I'm looking to start my adventures in CNC with a simple(and cheap!) MDF wood router to help me learn the ropes. The G540 sounds absolutely perfect for my needs and I am eagerly awaiting general availability in July. To Mariss or Marcus - do you have a distributor in the UK, or will I just be able to order directly from www.geckodrive.com? If so, do you have any idea what the shipping/import duty will be?
    Many thanks and brilliant job on the new drives - 6 months from concept to mass production is truly impressive!

    Matt

  16. #816
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    Aug 2005
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    51
    What kind of rpms can we expect for 3A stepper motors (with usable torque) from one of these drivers. I'm running .2" pitch ballscrews and am wondering if I can get good speed from the cheap drives or if I will need geckos and bigger motors. Any suggestions on 3A high speed motors that would work really well for these drives?

    John

  17. #817
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    Mar 2008
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    3655
    You need to look at more than just amps. IMO, Within their 3 amp/50 volt limitations, the Mighty Mites will run any motor that the larger Geckos will run. Top RPMs will come from running the motor at the highest (within the driver and motor limits) possible voltage.

    CR.

  18. #818
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    Jan 2007
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    Steve,

    The G250 will run any 3.5A motor just fine, but if the inductance is high enough it will take a higher and higher voltage to "push" the current through the windings. You can run a 10mH motor, but it will have miserable torque at 50V. Of course, the easy way around this is to buy a motor that has a lower L rating, but the world will not end if you run it at less than optimal voltage. What you will see is a low amount of torque for how many amps you are feeding it.

    John,

    The RPM will depend on many things, most notably your step pulse frequency. I can't say what your maximum RPM with useful torque will be because the definition of "useful torque" changes from person to person.

    Marcus Freimanis

  19. #819
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    Aug 2005
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    51
    Right now I have an old control system running pk266 motors at 45v and getting about 1.5in/sec on .2in pitch ballscrews @ about 1.5A/ph. I'd like to get more like 2-4in/sec, which would require 10-20 rps or 600 to 1200 rpm. Of course, these are like 110in/oz motors, so a motor upgrade would be necessary. I'm wondering if I can get 50 lbs of cutting force at the tool at 1200rpm with 3A steppers on .2" ballscrews and a motor recommendation for getting there. Maybe I just can't get there from the minigeckos...Dunno.

    thanks,
    John

  20. #820
    in-oz = 8 * Lbs / (pi * TPI)
    in-oz = 8 * 50Lbs / (3.14 * 5 TPI) = 25.5 in-oz needed

    Watts = in-oz * RPM / 1351
    Watts = 25.5 in-oz * 1,200 RPM /1351 = 22.6 Watts of mechanical power from motor.

    Easy! (use a 2A to 3A per phase motor @ 24VDC to 36VDC supply).

    Mariss

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