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Trying to get into electronics

Discussion in 'General Electronics' started by Balu, Sep 28, 2014.

  1. Balu

    Balu Veteran
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    Warning, probably stupid beginner questions and statements ahead. I'm mainly writing this together to sort my thoughts and experiences a little.

    So before starting something mechanical I decided to go and look at the electronics. To do so I've ordered a 4 axis CNC pack from eBay that had the following parts:
    • 4 Nema 23 stepper motors: Longs Motor 23HS9430B; 425 oz.in
      • Model: 23HS9430B
      • Step angel: 1.8 ┬░
      • Motor Length L: 115 mm
      • Rate Voltage: 6.4 V
      • Rate Current: 3 A
      • Phase Resistance: 2.1 Ohm
      • Phase Inductance: 9 mH
      • Holding Torque: 425 oz/in
      • Lead Wire: 4
      • Rotor Inertia: 0.89 kg/cm^2
      • Motor Weight: 1.55 kg
    • 4 Stepper motor drivers: Longs Motor DM542A
    • 2 Power supplies: 350 W, 36 VDC, 9.72 A
    • 1 Parallel breakout board.
    First I was surprised by the size and the weight of the motor and that it had shafts on both sides with different diameters. Neither shaft has a "flat" part where a setscrew might grab though - I'll have to see if that works mechanically later. Connecting it to the driver was simple since it was listed on the eBay page: black -> A, green -> A-, red -> B, blue -> B-

    [​IMG]

    The motor drivers seem to be fairly common, at least I've found some information on them. I like that I get a separate one for each axis - in case I blow one up, I don't have to replace a whole 4-channel board, just one driver by itself.

    [​IMG]

    My only problem is that I found two configurations. One where negative ports PUL- and DIR- share a common ground and the positive PUL+ and DIR+ are connected to the breakout board and another one where the common wire is the plus and the negative ones connect to the board. I have yet to figure out what exactly the differences between the two setups are. For now I've decided to go for the shared ground.

    As for the dip switches I did not touch them for now, so all of them are off.
    For the current table that means I get a RMS current of 3.0 A which corresponds to my 3 A motors, right?
    Also what is SW4 for? Off means "half current" On = full current"?


    I'm also a little confused about the motor voltage. It's listed as 6.4 V, but the power supply is 36 VDC.
    Do I have to step that down?

    I'm asking these voltage/current questions, because the motor got fairly hot. So hot in fact that I didn't want to hold it for longer than a few seconds.

    The pulse/rev table starts with 400, while I was expecting 200 steps. For me that means that I can not run at "full steps", but already have to start with 1/2 microsteps? Also I've read that microstepping more than 1/8th or 1/10th is not recomended which would mean, I'd set up the DIPs to have 1600 or 2000 steps?

    The breakout board is another problem. I had to look around how other people connected it, since I was not able to find a manual for it yet. It's a DB25-1205. I was just lucky that I was able to find others who had a working setup with this board - without really knowing the details either.

    [​IMG]

    So I connected 5 V from an old telephone charger to the board. I kept the two jumpers JN1 and JN2 that are supposed to connect the power between the separated inside/outside of the board, so I didn't have to use two 5 V power supplies. And finally I connected P2 and P3 to the driver PUL+ and DIR+.

    After switching everything on and not seeing any smoke I started LinuxCNC on an old PC and was able to fiddle about until I got to see the motor move.

    Things I have to figure out:
    • What is the best driver setup? Common ground or common positive? Is there even a difference?
    • Is it ok to have the "ENBL+" connected to 5V all the time? And why didn't I have to wire "ENBL-/ENB"?
    • Why is the motor getting so hot? Or is that normal?
    • Is my power supply voltage too high?
    • What is the "half current" setting on the driver for?
    • How many steps should the driver do for one revolution?
    • What is all the driver timing stuff LinuxCNC wants to know? :)
     
  2. Rob Taylor

    Rob Taylor Veteran
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    1) Yes. Depends on your PC's output. (How to determine that, I'm not sure)

    2) Yes. It's probably for PC control of power saving, so not really necessary. It just turns the driver on and off. ENBL- is apparently the same as DIR-, so just ignore it.

    3) It shouldn't be getting that hot, maybe back off the current to 2.5A or something. And double check you're not shorting it in any way, just in case the wiring diagram is incorrect for some reason. Looks like the setting you should have the first three DIPs on is ON-ON-OFF; 2.84A peak, 2.03A RMS. You could increase it from there gradually if that works nicely without heating up.

    4) Nope. Not for a NEMA 23. You can over-voltage steppers just fine, just don't over-current them!

    5) When the motor is stationary, this is the holding current- which will dictate the holding torque. Do you need it to stay in place strongly, or just sit there until it needs to move? Again, power saving measure.

    6) I'd start with 200, assuming the motors are standard 1.8 degree ones. I'm assuming this is ON-ON-ON-ON, since there's no option for this in the microstepping table. As you say, don't go below 8x microstepping if you want accuracy and repeatability. I'd stick with 4x, personally, unless your screw threads are really coarse pitch.

    7) No idea, I haven't tried LinuxCNC yet.

    I got all this from here: http://www.longs-motor.com/productinfo/detail_12_80_131.aspx - I think I've interpreted it right! Haha.

    Edit: Oh, and I just discovered Tweakie's Electronics 101 thread, which has some information you should find useful: http://www.openbuilds.com/threads/electronics-101.693/
     
  3. mulanima

    mulanima New
    Builder

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    Balu/Rob Taylor:
    Hi, how are you? I have the same or a very similar CNC KIT:

    http://www.ebay.com/itm/EU-US-Ship-...816?pt=LH_DefaultDomain_0&hash=item2c6da38c28

    I'm very beginner and i have a few question.

    1) Do you have any usefull wiring schematic? (something like this):

    [​IMG]

    2) I need connect to the board an emergency stop, a display, a joystick and an indexer (to run the file directly from a SD Card)
    Do you know if it's the right Breakout Board? The boards I've seen seeking for wiring diagrams look different.

    I thank you very much your help, sorry for the extremely basic questions.
     

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