1. #1
    Hello,

    can you please help me to choose electronics for my CNC. I was looking all over the internet about that and the more i read the less i know. Everything looked so easy at the beginning, but now looks like nightmare. I already spent half of my savings so i can't return now or quit.

    I already bought mechanics for my CNC. Table size would be around 1200 x 800 x 300 mm.

    I was thinking to buy nema 34 motors. Motor specifications are: 5.6 A/phase, 4.1 mH/phase, 7.7 Nm or 1090 oz-in, rotor inertia 1700g-cm2, 4 wire.

    Drivers for that are DQ860MA, and power supply 350W, 60 VDC for each motor.

    Can you tell me is that ok? Is the motor strenght enough for table with dimensions from above? I would like to mill in wood, aluminum and other soft materials. Can you also help me with driver settings. All those microswitches... i don't know where to begin. What current, how many microsteps...

    Sorry for grammatical errors, i am writing from Croatia.

    Regards, Domagoj

  2. #2
    Welcome to the forum, lots of useful posts about this subject so spend some time reading through them might be the best place to start.
    This is one of them:

    http://www.mycncuk.com/forums/faqs-p...do-i-need.html

  3. #3
    thanks for reply . In meantime i saw that link. I can find there usefull informations. When i come with some new questions, i will ask, but untill than does anyone have experience with drivers or motor that i am planing to use? I can't find users reviews or judgements for that tipe of drives. I found only reviews for 2M542 drives, but that is insufficient for nema 34 stepper motor.

  4. #4
    If you have a look at the build logs on the forum you will see that most people use nema 23 motors. These would be quite suitable for the machine you are building. Why do you want such large motors? You could save yourself some money by using nema 23 3.1Nm motors which would be up to the job, 7.7Nm is over the top for what you want to cut.

  5. #5
    I looked build logs, and will look more. First i also planed to use nema 23 425 oz (3 Nm) motors. The first time when i doubted about nema23 was when i took my linear rails. They were very heavy because they are also diy, and made from stainless steel. Second doubt was when i spoke with older guy from work. He also has cnc. He uses 9 Nm motors!!!! I said to myself then... WTF are you doing with 3 Nm motors? I think that gantry will in the end be around 20 to 30 kg. Is that heavy for 3 Nm nema motors? I have SFU 1605 ball screw. I would be happy if nema23 could do wood and some small aluminum things. My budget is weak and there is still a lot of work to do.

  6. #6
    What do you think about replacing my first choice (Nema34) with this components:

    3 x Stepper motors Nema 23

    voltage 3.78 V
    current 4.2 A/phase
    resistance 0,9 Ohm/phase
    inductance 3.8 mH/phase
    holding torque 3 Nm
    rotor inertia 810 g-cm2
    detent torque 1.2 kg-cm

    3 x Stepper motor driver M542H
    voltage 20 – 100 VDC
    current 1 – 4.5 A

    3 x Regulated power supply 48V 5A

  7. #7
    Quote Originally Posted by domagoj55 View Post
    What do you think about replacing my first choice (Nema34) with this components:

    3 x Stepper motors Nema 23

    voltage 3.78 V
    current 4.2 A/phase
    resistance 0,9 Ohm/phase
    inductance 3.8 mH/phase
    holding torque 3 Nm
    rotor inertia 810 g-cm2
    detent torque 1.2 kg-cm

    3 x Stepper motor driver M542H
    voltage 20 100 VDC
    current 1 4.5 A

    3 x Regulated power supply 48V 5A
    I would definitely use Nema 23 3Nm motors, thou those are slightly high on the Inductance at 3.8Mh I would look for some closer to 3mh or less.

    For best performance run them between 60-70Vdc. Voltage greatly affects the speed/torque you can achieve from steppers so is important to get size right.

    If you want really good drives then look at digital drives like the Am882 found here. Leadshine AM882 Digital Stepper Drive 80VDC 0.1A - 8.2A With Protection Function | eBay

    But which ever you choose they will need to handle more volts than you actually provide to the drives.? So say if you run them with 65Vdc PSU then use drives capable of handling 75Vdc. Don't run them with voltage near the drives Max capabilty.

    Regards the PSU then you don't need 1 PSU for each drive and can use just one PSU so long has it provides the Voltage and current(amps) needed.
    Also if your using 3 motors rated at 4A you don't need 12A PSU and can use 8-9A supply.? This is because you'll rarely if ever be using all motors pulling full amps at the same time.

    Often for larger supply's it's cheaper to build a toroidal PSU giving the exact power requirements needed. Unregulated Toroidal supply's are also better suited and preferred for the drives has they handle Back EMF better which stepper motors produce. They also provide consistent smooth power which drives like.

  8. #8
    Jazz thanks,
    i read a lot of posts on this forum. I saw that people really usually use only nema23 for hobby devices. So at the end i finished with three options. One that i already mention with nema23 motors (psu changed to 60v 600w). Price for that is around 450 $. Better nema23 kit is with nema23 motors with 2.5 mH inductance. That kit costs me around 500 $. The problem is that 500 $ is lot of money. I found also kit with nema23 3,8 mH and power supply 36V. I know what you and all guys said already, but difference between 250 $ for that kit and 500 $ for the best kit is huge. Is also difference in real world so huge? I did calculations with the cheapest kit, and with the most expensive kit. Both kit are fine with calculations. What should i buy? :(

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