CNC motor supply and choice

Other Hardware Motors, Mechanics, Power and CNC
1

Dear community!

I would like to build a little CNC machine with my arduino and wondered
what kind of steppermotors I should choose. I read a few things about holding torque,
newton/cm etc. but Im a bit confused.

I would like to buy a few of these:

The specs from the motor above:

  • 12V
  • 2 Phases
  • 0.33A
  • 0.23NM

So there are 2 questions:

  1. Is this motor enough for a lightweight CNC machnine build out of polysteren
    boards and a pen or cutter as plotting device (eventually even a dremel)? I would
    like to use the leadscrew approach.

  2. Using 4 motors means that I need a minimum of 2.64 Ampere (the one above
    needs 0.33A and has two phases, right?) + the amperes the control needs? What kind
    of power supply gives that amount of amperes? Is it possible to run with less?

Regards and thanks!

2

A love CNCs, I never assembled one, but I recomend to you to see this website:

This guy sells DIY CNC Kits. Watch the 'tutorials' video on how he builds, so you can have some ideas for parts and what you need.

They typically use Stepper Motors because of the accuracy, I like these:

They are practically industrial use, be careful with the power source, they typically need a reasonable current

3

Thanks for reply!

I will have a look on the links you provided.
But I already have choosen a stepper motor (see link in first post)! :wink:
Any suggestions on the 2 questions above?

4

Best is a PC power supply these are cheap compared to others.
There is no way of knowing what power of motor you will need with the scant information you have given.
I did something similar:-
http://www.thebox.myzen.co.uk/Hardware/CNC_Conversion.html

5
  1. The amount of push that your motor will provide is calculated by
    in oz. * TPI * pi / 8 = pounds of push
    Sparkfun and your datasheet do not report the torque (in. oz.) of your motor so kinda hard to calculate that one. Given that it's a NEMA 14 motor I'm going to guess 9 in oz, so that would mean if you were using a 1/4-20 leadscrew (20 TPI):
    9 * 20 * 3.14 / 8 = 70.69 pounds of push

Sounds like a crazy high number but that's how it goes. Of course, we're neglecting frictional losses here which should be at least 10% and the high TPI of the lead screw would result in a very slow movement rate. Also, stepper motors lose their torque as they spin faster.

...throwing that all aside and going by past experience I would not go smaller than a NEMA 23 motor. You will find that the increased cost is marginal.

  1. Only one phase of the motor is energized at any time so it's just .33A. As an aside, bipolar motors (like the one you have linked) have four phases. You do want a bipolar motor by the way as it will be much easier to find a controller for it, and look for a controller that has the ability to control the current to the motor as this will enable you to use higher voltages and get a little better speed from your CNC. Stepper motors are always rated with a voltage that will prevent them from burning out when a non-current-limiting controller is used (Ohm's law and all that).
6

Thanks for your input!

  1. Sorry, but Im using the metric system so what is exactly "in. oz." as well as TPI? :~
  2. The holding torque of the motor is "0.23N.M". -> newton per meter?

I will look at the producibility of this project hope I get it! :slight_smile:

7

"in oz" is "inch ounce" and "TPI" is "threads per inch". I don't have a metric formula.

"NM" is Newton meter. 1 NM = 141.92 oz in.

8

Ok!
There is definately a metric formula as well. I will google on that one!
Thanks! :slight_smile:

9

Definitely want to go for high speed bipolar motors if using a screw drive. A toothed belt drive will work OK with slow motors like those (but at the expense of precision of course).

The motors you've mentioned won't do many RPM because they are high resistance high inductance ones.

You first need to decide how fast you want "rapids" to be and design from there.