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    Default Microsteps too high?

    I am wondering if I have set my microsteps too high on my diy cnc mach. At first I was happy to find that I could get all 3 nema 23 motors to turn. I have an arduino/cncshield with drv8825 (all are Chinese if that matters). My axes are skate bearing trucks on angle alum (Solsylva) and they seem to move relatively freely. (I can turn the leadscrew with my finger with the motors connected). This is my first encounter with a cnc so I don't know exactly how easy they should move. Any way all the axes are moving when I jog the motors. The max feedrate is set to 500 (I think) and sometimes when I jog they seem miss steps.
    That's a pretty windy intro...sorry.
    I set the cncshield for 1/32 microstepping. Is that too fine? Would maybe 1/16 be better. Also by the way I set the vref to around .8 -.85 v.
    There are SO many variables involved here that my head starts spinning as I am unsure of what the base levels or starting points should be.
    Thanks
    Bruce

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    Default Re: Microsteps too high?

    1/32 micro stepping is probably too high, but is dependent on your screw pitch. What pitch lead screws are you using?

    As for the current setting, what are your motors rated for? With 0.8v ref, you are set at about 1.6A. The ref voltage should be set so the drive output current matches the max current rating of the motor.



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    Default Re: Microsteps too high?

    Forgot to put that in. Its a 5/16 - 18



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    Default Re: Microsteps too high?

    Cant find a datasheet. Its a LongsMotor 23HS8630 and I think it rated for somewhere between 2 and 3 amps. But at 1.5 amps the drivers are hotter than a two dollar pistol.



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    Default Re: Microsteps too high?

    First, You need better drivers for those motors. I found the specs and they are 3A motors, so running them at 1.6A is going to severely limit the torque the motor can provide.The motor wants the full 3A and about 40 volts. If you are below either of these you will hurt performance.

    At 18 TPI, and 1/32 microstepping, you have 115200 steps per inch. There is no way you need that much. I personally would reduce microstepping to about 1/8, and that is only for smoother operation, not for resolution.

    Also, at your settings you are at a stepping rate of 37,795 steps/sec at your max feed rate of 500mm/min. This exceeds the recommended maximum for Grbl and could cause problems.



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    Default Re: Microsteps too high?

    Thanks a lot for the help. That's good information. I am going to drop the steps and the feed rate. I will probably have to go with a TB6560 if I want higher amperage, but I wanted to avoid that because I already burned one up just jogging the machine. Also I will have to figure out how to control them with an arduino because I don't have a parallel port computer anymore. So if I can stick to an serial port control I'll be able to afford to keep trying.
    Thanks again.



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    Default Re: Microsteps too high?

    The TB6560 is not a very good choice. I would suggest that since you are using an Arduino and CNC shield, I believe that the shield has provisions for using external stepper drivers rather than the plug-in DRV8825.

    I would recommend the DM542T from Stepper Online. I have these on a machine I built and they work really well. The cost more, but they have mid-band resonance dampening, idle current reduction, 4.2A and 50V capability. They are very very smooth. I believe they are made for Stepper Online by Leadshine. They cost about $33 each from Amazon. The thing I like about these are they work exactly as advertised with no monkeying around.
    https://www.amazon.com/STEPPERONLINE...+driver+DM542T

    If the DM542T is out of your price range then the TB6600 drives are cheap and a better choice than the TB6560. On my machine that has the DM542T's, I started out with TB6600's like the ones in the link below. I like individual drives for replacement ease. The TB6600's worked fine, but they can only be driven to about 40V. I used 36V and did not have a problem. I replaced them only because I wanted more speed and was going to up the voltage to 48V. At 36V the TB6600's worked fine, but they are not as smooth as the DM542T drives, but are a lot cheaper at about $8 on ebay. Takes a month to get them though. They also have some issues in regard to how they are made and setting VRef for the current. Basically the problems limit them to something less than the advertised 4.5A, but for my application I was looking for only 2.8A. See this thread for an explanation:
    http://www.cnczone.com/forums/steppe...ml#post1979892

    This is the type TB6600 drives I have used. https://www.ebay.com/itm/4-5A-TB6600...IAAOSw4shYBx~-

    Bottom line is that the TB6600 drives are the lowest price/quality drives I would ever use now. I did start out on my first machine with TB6560 drives, but the TB6600's are a step up, and the DM542T drives are very good. Stepper drivers are definitely a place where you get what you pay for.

    Note: I also have DRV8825 drives on my 3d Printer and they are great little drives, but no match for a motor that needs more than about 1.5A.



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    Default Re: Microsteps too high?

    BTW, You can use an Arduino and drive a parallel port type CNC just fine. The link below gives an idea of how I did it for my first machine to try GRBL. That machine usually runs with LinuxCNC, but the little Arduino runs it just fine.

    http://www.cnczone.com/forums/bencht...ml#post1673326



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    Default Re: Microsteps too high?

    I will definitely look into these dm542t. Maybe it will save me from throwing away time and money. Thanks



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    Default Re: Microsteps too high?

    fwiw I think I discovered the biggest hitch I was having. It seems that I was using an Arduino clone with a ch340 chip instead of the 16u2. I changed to another arduino (still a clone but it has the atmega chip). Now even with the motors drawing only about 2 amps, it is running so much more smoothly. Its not jumping steps. I cut back from 1/32 to 1/8. I have ordered some tb6600 that will allow me to kick up the amperage to 3 amps and I think the motors will run smooth as glass. Thanks for all the help.



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    Default Re: Microsteps too high?

    Quote Originally Posted by bwg View Post
    fwiw I think I discovered the biggest hitch I was having. It seems that I was using an Arduino clone with a ch340 chip instead of the 16u2. I changed to another arduino (still a clone but it has the atmega chip). Now even with the motors drawing only about 2 amps, it is running so much more smoothly. Its not jumping steps. I cut back from 1/32 to 1/8. I have ordered some tb6600 that will allow me to kick up the amperage to 3 amps and I think the motors will run smooth as glass. Thanks for all the help.
    I highly recommend not using the ch340 equipped arduinos for CNC, but I would bet that the problem you were having was the high microstepping rate that resulted in a step rate of 37kHZ. Grbl is only good to about 30kHz. Beyond that, things can get wonky. The CH340 will only cause command streaming errors to Grbl, and usually only of you are sending commands very fast. The "smoothness" of the step signals is entirely within the Arduino's 328P chip, but as said, above about 30kHz it can basically overtax the 328P resulting in problems.

    Glad you got it working better.



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    Default Re: Microsteps too high?

    Was asked how to wire the TB6600's to Grbl. Here is how I did it.

    Microsteps too high?-grbl-tb6600-hookup-jpg



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    Default Re: Microsteps too high?

    Thanks a million John. This will help greatly and might prevent my frying my new chips.
    Bruce



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Microsteps too high?

Microsteps too high?