Help with Grbl Mill Steppers stalling....

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Thread: Help with Grbl Mill Steppers stalling....

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    Default Help with Grbl Mill Steppers stalling....

    I'm in the process of building a 450x450mm Grbl Mill
    Uno with Grbl sheild
    Drv8825 drivers
    Nema 23 stepper 2.5a

    5mm pitch ball screws.

    I cant get the thing to go beyond 1000mm/min rates. I have been all over the board with the Grbl settings.
    I plan to machine at 50-75in/min and it wont rapid half that speed.

    Driver set to full steps.
    vref 1.25

    If I go above 1000mm/min it stalls. if I touch the ball screw at 900mm/min it stalls.
    No binding, everything moves free manually.

    If I run a program just stroking a axis (G0X0;G0X450.00. repeat) neither the driver or stepper gets above ambient temp.
    I would think if i'm pushing it too hard the drive would at least get warm if not HOT....

    Any ideas?

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    Default Re: Help with Grbl Mill Steppers stalling....

    Are you sure that you have set vref correctly? Mine drv8825 are really hot when set for 2+ amps(like 60 or 70 degrees Celsius), but I have tuned grbl to keep steppers always on because my router is without counterweights on z-axis. Also there no point in using full steps, 1/4 or 1/8 will give much smoother movement.



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    Default Re: Help with Grbl Mill Steppers stalling....

    What voltage are you running to your steppers? What is the maximum voltage you stepper drivers can handle? Doubling voltage increases available torque by 4-10 times. Moving from 20 volts to 48 volts on my Arduino controlled rotary table solved a lot of problems and avoided the need to replace the rather small Nema 23 stepper. LinuxCNC has taken a Nema 23 269 oz/in stepper motor with the same driver and power supply combo to a velocity of 6600 mm/sec and acceleration of 2500 mm/sec/sec. It won't be anything to do with grbl, it will be how you have set up the external components.

    Rod Webster
    www.vmn.com.au


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    Default Re: Help with Grbl Mill Steppers stalling....

    Quote Originally Posted by kfmut View Post
    Are you sure that you have set vref correctly? Mine drv8825 are really hot when set for 2+ amps(like 60 or 70 degrees Celsius), but I have tuned grbl to keep steppers always on because my router is without counterweights on z-axis. Also there no point in using full steps, 1/4 or 1/8 will give much smoother movement.
    started with vref at.9 (conservative) cranked them up to 1.25 (2.5a) last night no change
    using full steps for now just see see if that was causing torque loss. Plan on running 1/4steps =6.5 micron resolution in the end.



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    Default Re: Help with Grbl Mill Steppers stalling....

    Quote Originally Posted by rodw View Post
    What voltage are you running to your steppers? What is the maximum voltage you stepper drivers can handle? Doubling voltage increases available torque by 4-10 times. Moving from 20 volts to 48 volts on my Arduino controlled rotary table solved a lot of problems and avoided the need to replace the rather small Nema 23 stepper. LinuxCNC has taken a Nema 23 269 oz/in stepper motor with the same driver and power supply combo to a velocity of 6600 mm/sec and acceleration of 2500 mm/sec/sec. It won't be anything to do with grbl, it will be how you have set up the external components.
    I think this may be part of my problem,
    running 12v 300wPS I think I have a 48v laying around. The stepper are 4v 184oz. Not sure what the max is.
    Think I'll try increasing voltage since the drivers are staying cool thats telling me there is not enough power moving through them
    Then if that does not work ill be moving toTB6600 drivers.



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    Default Re: Help with Grbl Mill Steppers stalling....

    I really don't want to go to 32 stepper and from what I have seen online I should not have too.
    If the PS upgrade does not help nor the driver upgrade I may move to a 4a 2500rpm nema 23 from mcmaster with the TD6600 they are a bit salty ($55 but might be the better option in the long run.

    I have been playing with Arduino for years and am a 20+ year CNC programmer/Manufacturing engineer. But Grbl seems to be kicking my butt!



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    Default Re: Help with Grbl Mill Steppers stalling....

    For the drv8825, 45volts is the maximum. To be safe, I wouldn't use more than 36volts. At 36volts they do get really hot so fan cooling is needed. Most don't run more than 24volts since that is a popular power supply size.



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    Default Re: Help with Grbl Mill Steppers stalling....

    DRV8825 drivers:

    2.5 amps is MAXIMUM CONTINUOUS CURRENT. Pololu recommends 2.2 Amp Max
    To run at this would require very good heat sink attached to bottom of chip. Boards designed for nema 17 steppers will run warm/hot at 1.8 amps

    At full step mode this chip runs at 71% of current so you are better with microstepping.

    Current setting of Vref depends on sense resistors used., current = Vref/(5 * Isense resistor )
    Pololu steppers use 0.1 ohm so current = Vref/5 * 0.1 .9 = .9/.5 = 1.8 amp
    If current set resistors are different then setting changes. Some boards use 0.05 ohms so current is 1/2 as high

    12 Volts is low for running nema23 steppers due to there higher inductance.( Look for low inductance motors to get maximum speed )
    48 Volts is over rating for Pololu boards



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    Default Re: Help with Grbl Mill Steppers stalling....

    I ordered a 0-48v variable 450w PSU should be here tomorrow.
    I will play with the Volts to see where it gets me



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    Default Re: Help with Grbl Mill Steppers stalling....

    Well I found a 48v PSU in my "Arduino crap" tote.I was able to dial it down to 42v
    NIGHT AND DAY DIFFERENCE!
    With no load other than the ballscrew carrying the x axis bridge I was able to get to 5500mm/min but needed 150 on the accel. 4000 smooth with accel at 1500. Better buy not where I want it. I think I'm going to goto 4 or 6 amp motors and driver. In the end I would really like to see 10k+ on rapids. shooting for 500IPM. I know it will work slow and in the end may be better for accuracy but I had a goal in mind and want to get there. If it dont work fast so be it. 4000 is still better than 900.

    In the mean time I found a really cool and cheap PSU on amazon I wanted to share is anyone is following.
    It's variable from 0-48v with a digital read out and large POT. They make it in 0-48 and 0-24. I plan to relocate POT and readout to the front of my project box so I can easily tune it down for light machining and crank it up for heavier cuts.
    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1



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    Default Re: Help with Grbl Mill Steppers stalling....

    you wont be able to get 500ipm in your 400mm work space. 200ipm is what you should just realistically go for.

    Luthier/Woodworker/Machinist in NS, Canada.


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Help with Grbl Mill Steppers stalling....

Help with Grbl Mill Steppers stalling....