Stepper selection

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  • October 22, 2011 at 8:48 am #1820
    bart_janssen
    Member

    Hi,
    I’m in the process of selecting a steppermotor to be used in the conversion of my proxxon KT150 XY table to CNC.
    I’m planning to use an arduino with the GRBL shield to control it.
    What confuses me a bit is the statement it can drive up to 2.5A per winding. Does this mean it can handle a total of 5A per motor?
    Initially I was looking at this motor:
    http://www.damencnc.com/files/manuals/DCNC-NEMA23-2.5-NM.pdf
    The power rating given is: 3A unipolar, 2,1A series, 4,2A parallel
    Now I’m not sure if it’s going to work. Would a smaller one be a better choice?

    Thanks!
    Bart

    October 22, 2011 at 10:19 am #1821
    alden
    Member

    Bart,
    This motor should be fine if you wire it up in series mode. The drivers on grblshield are Texas Instruments DRV8811’s which are bipolar drivers that can supply up to 2.5 amps per phase. The data sheet for the drivers is on our github:
    https://github.com/synthetos/grblShield/tree/master/references

    So as long as you wire the motors in series mode they will take a max of 2.1 amps per phase. The wiring for series is on the motor data sheet you referenced. Series wiring means that the ends of each coil are wired to the plug, and middle leg of each phase are floating (unattached to anything) (I realized that this last statement may be confusing – Referencing the motor data sheet – the “middle wire” is the blue-connected-to-yellow, and the brown-connected-to-orange. Many unipolars are 6 wire, looks like this one is 8 wire where the above connections connect the middle. It would be easier to explain if I could draw a picture).

    Let us know how your project goes. – Alden

    October 28, 2011 at 8:01 am #1822
    bart_janssen
    Member

    Just received a notification my steppers are in the mail. Deceided to go with a smaller (and cheaper) model since i wouldn’t be able to get the full power from these.
    I’ll let you know when i have them running.

    December 28, 2011 at 7:31 pm #1823
    bart_janssen
    Member

    Ok. I bought these steppers and a MeanWell 24V 13A powersupply.
    http://www.damencnc.com/files/manuals/DCNC-IP54-1NM.pdf
    Checked the PSU to see if the polarity markings were correct and connected it to the grblShield. Then connected the stepper to the shield and applied power to see if the led lit up. It did.
    Turned off the PSU and plugged the shield into an arduino duemilaneuve with GRBL on it and connected the USB cable to my computer. Started processing to run the gctrl.pde sketch. Error RXTX version missmatch. Downloaded the latest version and removed other versions.
    When I now run the sketch again it returns no errors and the console says: Grbl 0.6b
    ‘$’ to dump current settings
    When I open a gcode file it seems to stream ok. Console shows the command followed by an OK from GRBL.
    Problem is when I look at the stepper nothing appears to be happening. Did I miss something? Tried to raise the current but that doesn’t seem to make any difference.

    Any help would be greatly appreciated!
    Thanks! Bart

    December 29, 2011 at 10:14 am #1824
    alden
    Member

    What is the source of your grbl .hex file? Some of the earlier 0.6 versions did not activate the Enable bit correctly (it should be active LO for the steppers to be enabled). If you have a scope you can see the Enable on Arduino D8. On the v2 grblshield the Enable pin is labeled “enable” on the board on the J6/J7 connectors. On the v1’s it’s the unlabeled pin below the ‘9’ pin on the J6/J7 connectors. You can find schematics for this on the grblshield github.

    A change was made to Simen’s grbl github Edge branch to fix the enable sense, and the 0.6 from there should work. As fas as I know this patch has not made it back to the Master branch. However, since this all transpired last Spring/Summer Sonny Jeon (chamnit) has fixed a number of grbl issues his grbl fork , and we recommend using his 0.7 branch. (We are still testing the 0.8 alpha branch.)

    Pointers to whatever the latest recommendation can always be found here:
    http://www.synthetos.com/wiki/index.php?title=Getting_grbl

    Hope this helps. – Alden

    December 30, 2011 at 7:51 am #1825
    bart_janssen
    Member

    Thanks. Since I don’t have the AVRISPMKII programmer I used avrDude to flash the arduino with the 0.7 version. That looks like it made a difference. The green LED’s D2, D3 and D4 now light up and blink when I try to stream a g-code file. The motor now makes al little noise aswell but still doesn’t turn. Unfortunately I don’t have the time to look into it a bit more right now. Don’t suppose it matters there is only 1 stepper connected?

    December 30, 2011 at 9:29 am #1826
    alden
    Member

    Yes, that sounds like progress. At this point the next things to look at is (1) do you have your motors wired correctly, and (2) do you have adequate current to them?

    Check motor wiring against the motor pinouts and current settings at the following link:
    http://www.synthetos.com/wiki/index.php?title=Using_the_grblShield

    These may also be useful:
    http://www.synthetos.com/wiki/index.php?title=Wiring_TinyG
    http://reprap.org/wiki/Stepper_motor

    Alden

    February 9, 2012 at 11:48 am #1827
    bart_janssen
    Member

    Got it working now. The current pot needed to be adjusted more precise than I was doing. Going between not enough current and to much. Both result in the stepper making noise but not rotating. Doing the same in smaller increments made me find the right position.
    Thanks for your help!

    March 13, 2012 at 5:29 pm #1828
    bart_janssen
    Member

    It took a bit longer than expected but I have converted the proxxon machine and all is running well. At least for the first minute, then the x-axis starts stuttering. I believe this may be due to the driver shutting down because it’s overheating. I’ve lowered the current a bit and it seems to help a little. The x-axis had a bit more frinction than the others. Would it reduce the load on the driver if I try to resolve that? (not looking forward to take it apart again..)
    If I were to order the heatsinks, how do they attach to the board? Are they just soldered on to the board?

    March 13, 2012 at 7:18 pm #1829
    alden
    Member

    It does sound like you are experiencing thermal shutdown. I’d look first at the mechanical system. This is usually the root of the problem – at least if the Y axis is fine and it’s running the same type of motor. Would this be the Proxxon Micro Mill MF70? How hard is it to hand crank the X axis? It could be that you need to loosen the jib screws on the X axis ways. Or perhaps it needs some way oil. Or perhaps the lead screw is binding. Does the friction seem worse at either end of travel and less in the middle? Could be a jib alignment problem. Finding the source of the mechanical issue is the best solution, if indeed it is a mechanical issue.

    What stepper motors are you running – manufacturer, model number, and preferably a link to the spec sheet if you can find that. Roughly how far up do you have the current setting trimpots? All the way, 80%, 60%?

    If none of this works then the heatsinks would help, but if you are pushing the envelope you will also want to fan cool them. They attach just by peeling and sticking – no soldering is required.

    March 18, 2012 at 7:02 am #1830
    bart_janssen
    Member

    Thanks for the tips.
    I took the spindle out and saw the allignment could be imroved. Also worked on the delrin nut a bit and it is running mutch smoother now.
    It was still overheating but a lot less often. Made a little heatsink out of a square piece of brass to see if that help and it works like a charm.

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