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  1. #1
    Join Date
    Sep 2011
    Posts
    10

    Stepper motor too slow !!

    Hello, This is my first CNC machine and I ran into a problem with the motors or drive system, They seem to be running too slow, I mean about 5 min just to move 3 cm with no load !

    I bought this kit http://www.download.sstecnica.com.ar..._MAXI_2311.pdf, consisting of a parallel port interface, 3 10A microcontrolled driver boards, 3 motion king 23HS6602 hybrid stepper motors and a standard 500 Watt pc power supply.

    I built a basic frame about 50cm wide by 60cm long, using and unsupported course thread screw and a 2.12mm pitch.

    I talked with the supplier of the kit and he helped me step by step to configure TurboCNC and MAch3 with same results, we played around with varios settings trying to increase pulses but motor will stall.

    Now I read a little and decided to test motors with a bench top, regulated supply at 12V 1.5A and motors seem to run a little faster but I lost torque, I can stop the gantry with one finger.

    I have some questions which I haven´t been able to answer, for example..

    1. what are these motors working frequency or RPM?

    2. what voltage should I feed the motors (5V,12V,24V etc)

    3. supplier of kit says if I install larger motors I will only gain torque not speed. Is this true?

    Also looking at the driver boards I do not see any sense resistors, normaly 1 ohm 2 - 5 watts, nor do I see a similar sense scheme as the linistepper yet it is advertise as soo..

    So if you can shine some light as to why this happens or how to solve it I would greatly apreciated..

    Motor Specs (23HS6602):
    23HS Stepper Motor 57mm 1.8degree, MotionKing Stepper Motor

    Step Angle (deg): 1.8

    Motor Length (mm): 55

    Rated Current (A): 1.5

    Phase Resistance (ohm): 3.2

    Phase Inductance (mH) : 5.5

    Holding Torque (N.cm Min): 80

    Detent Torque (N.cm Max): 3.5

    Rotor Inertia (g.cm²): 280

    Lead Wire (No.): 6

    Motor Weight(g): 680
    Attached Thumbnails Attached Thumbnails Kit02_CNC_14_3Kg_3Axis.jpg  

  2. #2
    Join Date
    Oct 2008
    Posts
    406
    With a motor inductance of 5.5mH, you need a 75 volt supply to get full power. A 12 volt supply won't work very well.
    Bob

    "Bad decisions make good stories."

  3. #3
    Join Date
    Jan 2010
    Posts
    2141
    Also, what microstepping mode have you chosen? (1/4, 1/8, 1/16 or something else)?

    Is there any provision on the driver boards to set the current? You say that you can't identify any current sensing resistors, but there must be some way of setting the current on the driver boards.

  4. #4
    Join Date
    Sep 2011
    Posts
    10
    bobsch:

    Board provider tells me not to use over 5V and I have not dared to use over 15V in fear of burning the motor cause of the fact that I don´t know whether the driver board can regulate current.

    doorknob:

    The board has no way of setting current, it only has a jumper to select full step and half Step. Which I tried both.

  5. #5
    Join Date
    Jan 2010
    Posts
    2141
    I do not speak Spanish, and google translate did not do a very effective translation job, but based on what you stated and what I read, it looks like those driver boards are very simple, using an H bridge to single step or half step the unipolar motors.

    So it should be fairly straightforward to figure out the winding current that the motor is actually drawing compared with its rating. For example, you could use a multimeter inline with the motor power supply while there is a holding current on the motor. Depending on the design of the driver board, either one half winding or two half windings will be energized at the same time (depending on whether it follows the pattern in figure 1 or figure 2).

    Do you know what the step pulse width is from Mach3? By any chance do you have access to an oscilloscope? Perhaps your step pulse width is too short for the driver to handle properly. What step pulse repetition rate are you using?

  6. #6
    Join Date
    Sep 2011
    Posts
    10
    Quote Originally Posted by doorknob View Post
    Do you know what the step pulse width is from Mach3? By any chance do you have access to an oscilloscope? Perhaps your step pulse width is too short for the driver to handle properly. What step pulse repetition rate are you using?
    Do you mean the kernel frequency ? this is set at 25000 Hz.

  7. #7
    Join Date
    Sep 2011
    Posts
    10
    While I resolve this problem, I would like to upgrade the motors for more torque, I believe these are small.

    Can someone tellme what motors would be good, I have a contact in miami who is going to send them, perhaps something from ebay I don´t know

  8. #8
    Join Date
    Jan 2010
    Posts
    2141
    Quote Originally Posted by abel2b View Post
    Do you mean the kernel frequency ? this is set at 25000 Hz.
    OK, that info is useful. What is the pulse width?

    It looks like there may be a low-end microcontroller on the driver board that is translating the step and direction pulse input into the coil energizing sequence for the motor. I was wondering whether that microcontroller might be having a hard time accepting short step pulses (or too-fast a pulse repetition rate).

    Have you tried using a relatively-long step pulse width (such as 10us or 15us)?

    And yes, 80 N-cm is roughly 110 ounce-inches, which is somewhat less holding torque than typical motors used with home-built CNC machines (although some of the smaller machines do use motors of that size). Many people are using motors rated in the general range of 250 to 500 ounce inches of holding torque.

  9. #9
    Join Date
    Sep 2011
    Posts
    10
    Thanks! you have been most helpful...

    I asked supplier of board and he says the boards acepts a minimum of 20us and max of 30us pulse width and he recomended to use 20us.

    we are looking at buying this motor Green Monster 400 OzIn 8-Wire Stepper Motor - but we have dought as to my driver boards also I am not inspired by boards from this company sooo... this kit is my alternative 3 Axis Drive Stepper Motor 270 Oz-in CNC Kit, P.Supply | eBay

    What you think ??

  10. #10
    Join Date
    May 2010
    Posts
    290
    The Sherline 1/2 pulse mode can be helpful as well in dealing with drives that need a lengthy pulse.

  11. #11
    Join Date
    Jan 2010
    Posts
    2141
    Quote Originally Posted by michaelthomas View Post
    The Sherline 1/2 pulse mode can be helpful as well in dealing with drives that need a lengthy pulse.
    That's an interesting suggestion - in order to get about a 20 us pulse in Sherline mode, would the kernel speed need to be increased to at least 35kHz?

    But maybe 25kHz will be OK, even though the pulse will be longer than the recommended maximum (per the board vendor).

  12. #12
    Join Date
    Jan 2010
    Posts
    2141
    Quote Originally Posted by abel2b View Post

    we are looking at buying this motor Green Monster 400 OzIn 8-Wire Stepper Motor - but we have dought as to my driver boards also I am not inspired by boards from this company sooo... this kit is my alternative 3 Axis Drive Stepper Motor 270 Oz-in CNC Kit, P.Supply | eBay
    There may be better people to give you guidance about the best motor size to use for your size of machine, however I believe that a lot of people on this forum use something like the following:

    Page Title

    Gecko Diver G540 3 axis kit (One G540 + Three
    NEMA 23 KL23H284-35-4B (1/4” Dual shaft with a flat) 387 oz-in +
    one KL-350-48 48V/7.3A 115V /230V power supply: $455.95

    As for the eBay driver and motors, some people have acceptable results with that driver, but some other people have reported problems. There is a long but informative thread that discusses that board at:

    http://www.cnczone.com/forums/genera...y_chinese.html

    The 400 ounce-inch stepper motor from probotix may be big enough for your machine, but your driver will not be able to do a good job with that motor because the driver can not handle a high enough voltage to give adequate performance.

  13. #13
    Join Date
    Sep 2011
    Posts
    10
    I will try that tomorrow !! I just caught a nasty cold

  14. #14
    Join Date
    May 2010
    Posts
    290
    Yes......35000 to 45000 would put the pulse in the range the manufacturer suggests.......although 25000 may be ok.

    I think Mach tops out at 15us in the standard mode.

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