Upgrading my MPCNC

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This topic contains 16 replies, has 2 voices, and was last updated by Profile photo of Ryan Ryan 1 week, 4 days ago.

Viewing 17 posts - 1 through 17 (of 17 total)
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  • #35787
    Profile photo of gbiski
    gbiski
    Participant

    Hello,

    I am trying to upgrade my MPCNC.
    As a first step I lowered a few days ago at half the z axis cutting length from 19cm to 9cm.
    In my machine i have an arduino shield with an arduino uno (I am running gbrl) and my steppers are at 0,9 angle at 1,7A per coil with a holding torque: 48N.cm – 4.8kg.cm.
    The new that I have ordered are at 1.8 angle , 2,0A rated current and a holding torgue at 8.2 kg.cm.
    Do you believe these steppers are a significant upgrade in the strength of my machine ? Today I am facing often issues in hard materials even if a slow down the feeds….
    One of my main concerns with the new steppers is the current limits.
    I am jumping from 2 steppers per A4988 at 1,7A current to 2 steppers at 2A.
    Do you thing that i will be ok and i will not burn the system ?

    • This topic was modified 1 week, 5 days ago by Profile photo of gbiski gbiski.
    #35791
    Profile photo of Ryan
    Ryan
    Keymaster

    What issues are you having?

    Are you wired in series? Do you have a cooling fan on the drivers? You will most likely not be able to run them at full power, but no one ever does as the steppers get too hot anyway.

    #35793
    Profile photo of gbiski
    gbiski
    Participant

    I did not yet connected the new ones. I plan to do it on the weekend.
    The current ones are wired in series as your build guides and i will do the same for the new ones.
    I do have a cooling fun.
    Today i have the A4988 at 0.6A vref and i have a second setup with DRV8825 at 0.8 vref.

    Do you believe is a good upgrade the new steppers ?

    #35795
    Profile photo of Ryan
    Ryan
    Keymaster

    What problems are you having that makes you think you need to change them?

    Those voltages actually seem pretty high, at 0.7V on a drv8825 my 76oz/in steppers wired in series are as warm as I would want to run them at.

    #35796
    Profile photo of gbiski
    gbiski
    Participant

    Today my issues are steps lost if the material is not soft enough so very often it ends up with a bad results or even destroyed material…. Thu I am getting inconsistent cuts.
    In a previous conversation that we had on the forum on that topic you have commented that:

    ” With a .9 degree step angle I think your torque vs speed curve is even worse. Our top speed is probably double yours. You need to find the torque curve specs for those steppers. we drop off at 60rpms, you probably drop off at less. those are high accuracy steppers not high speed. You might just be fighting a power/rpm issue”

    So i thought that if i switch from .9 angle to 1.8 angle and from a stepper with a torgue of 4,8 kg.cm to 8.2 kg.cm i will upgrade significant my machine and i should most probably do it more rigid and fast….

    What do you thing ?

    #35797
    Profile photo of Ryan
    Ryan
    Keymaster

    Yes, I still think that is all true. What kind of speeds are you trying to get? I ran just fine through aluminum with 42oz/in wired in parallel and never missed a step on the XY axis.

    If you already have the new steppers you might as well use them, If you don’t I am willing to spend some time helping to see if money should be spent.

    #35799
    Profile photo of gbiski
    gbiski
    Participant

    I already ordered them and are on their way to Greece….
    I tried to cut aluminium on the machine and the only way to do it was with feed rate 125mm/min, plunge at 70mm/min and depth per pass 0,1mm. Even with these i had to through some drops of water constantly on the aluminium in order to avoid issues.

    On wood (pine which is soft) i am using feed rate 350mm/min, plunge at 130mm/min and depth per pass 0,7mm.
    And before lowering the Z axis even with theses rates i had some issues….

    On aluminium this is my best reult so far

    For the A4988 the 0.6A is a good Vref ?
    The 2.0A new steppers anyway would not cause any issues on the electronics setup that i have ?

    thanks for your help Ryan

    George

    #35803
    Profile photo of Ryan
    Ryan
    Keymaster

    Those rates are extremely slow. Let’s not dive into the aluminum here, but in the wood that is crazy slow and shallow. Something else has to be wrong. I can very easily cut extremely dense wood at 4mm depth at 15mm/s (900mm/min). What stepover are you using, what kind of bit, what spindle, how big is your machine in usable work area XYZ?

    That video looks much much faster than 2mm/s (125mm/min)

    You keep saying issues, you should really expand on what that means.

    #35804
    Profile photo of Ryan
    Ryan
    Keymaster

    If it is the machine on your youtube, you have the zaxis assembled wrong. the lower mount is there for a reason and it needs to touch the coupler. That cable chain attached to the Z axis is also a really bad idea.

    #35805
    Profile photo of gbiski
    gbiski
    Participant

    Sorry Ryan I lost you.
    What do I have to correct on the z axis ?

    #35806
    Profile photo of Ryan
    Ryan
    Keymaster

    The lower z bracket, and you should really not use a cable chain on it.

    Z Axis

    #35807
    Profile photo of gbiski
    gbiski
    Participant

    Yes I saw these 2 things that you have noticed. I will correct them!!!!

    As far as the new steppers (as I already are in transit) is concerned what vref do you thing I must use in order to gain more torque than today (connected in parallel) ?
    I do not know if I leave the settings in A4988 at 0.5- 0.6A vref and the DRV8825 at 0.7-0.8 vref I will get the additional (double) torgue that the new steppers have or I will get the same torgue as today….

    #35808
    Profile photo of Ryan
    Ryan
    Keymaster

    I can’t comment on the a49 drivers I have not set one in years.

    Wire them in series and set the drivers to deliver about 85% of the max rated current.

    #35809
    Profile photo of gbiski
    gbiski
    Participant

    Do you have any good guide on wiring in series ?
    I have to purchase additional materials ?

    #35810
    Profile photo of Ryan
    Ryan
    Keymaster
    #35811
    Profile photo of gbiski
    gbiski
    Participant

    As I do not have your wirring kit I just connected them like this:

    https://www.vicious1.com/wp-content/uploads/2015/09/wiring.png

    I think my connection is parallel and not in series ….

    I need to do this ?
    https://www.vicious1.com/wp-content/uploads/2016/08/IMG_20160829_150944.jpg

    #35818
    Profile photo of Ryan
    Ryan
    Keymaster

    Series will give you more power. You are wired in parallel.

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