Author Topic: CNC machine - do I need a controller? How about a driver?  (Read 1625 times)

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Offline aljaffeeTopic starter

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CNC machine - do I need a controller? How about a driver?
« on: June 10, 2009, 07:12:27 AM »
OK, I had a previous post and SmAsH and GearMotion helped me out with some answers and I thank you both.  Basically, I am completely new to this and I have been doing as much research as I can about robotics on the internet.  What I have found is that the project I am attempting to build is similar to something called a CNC machine (look it up on YouTube for some interesting videos if you have never seen this kind of machine before).  Also, it is sometimes called an XYZ table or XYZ positioner.  Many people make CNC machines to be like robotic routers, milling machines, or lathes.  My planned application is not that heavy duty.  I will simply be moving around (X and Y axis) a lightweight wood or plastic plate and having an overhead (Z axis) arm drop down and make marks on the plate where appropriate.  So, the CNC machine would only be moving around a piece that weighs about 1 or 2 pounds (.45-.90 kg) total.  I will not have an electric drill or anything like most CNC machines have.  My ideal design is like this ( (I know this is only a picture of an XY positioner, but I am still deciding how I want to design the "Y" axis part).

I want to have my laptop to be connected to this whole thing and control it all.  Ideally, I would also like not to have to use a lot of electricity if possible.  Also, I want to connect to my laptop using the USB port(s).  Basically, from what I have seen on the internet, aside from the CNC machine itself, I need to buy/or build 2 other machines - one is called a "controller" and the other is called a (motor) "driver."

Earlier, GearMotion had suggested that I use the U401 and U421 USB interface (  If I use that, does that replace the controller - or is it simply an adapter between my laptop's USB port and the controller?  Or can I turn the U401 into a controller?  Or is the U401 completely unsuitable for my project now that you know this new information from me?  Can I simply stack some Dontronics things ( onto the U401 to enhance the capabilities of the U401 like they suggest on this website:  Or is this not suitable for my project?

If I need to have a controller, what is the best/most economical way to buy or build one?  Most of the controllers I have seen on the internet are several hundred dollars like this:  I can't afford that.

I have found another lower price controller like this one as well:  Is that suitable for my project?  I notice that this one has something called a PIC.  Do I need that?  I thought I could just use my laptop to do any processing and for any real-time memory (RAM)?

What is the benefits of a controller over just using the U401 USB interface?  Does a controller make sure that no more than 5v gets returned to your laptop in any of the input sockets of the USB (so that you don't fry your laptop)?  Is that the only advantage?

This person has made a low cost CNC machine ( and he gives his schematics for the controller he designed ( (  Would this be easier to make and cheaper than buying the one I mention above (

As I understand I need to use stepper motors called "NEMA" motors.  This is some kind of standard.  Is it safe to assume that all other kinds of stepper motors are unsuitable to use?   That is, are all other stepper motors not strong enough or smooth enough?  I ask this because sometimes it seems that NEMA stepper motors are more expensive than non-NEMA stepper motors.  Or is it a federal regulation that only NEMA approved motors can be sold in the U.S.?  Also, if I use NEMA stepper motors, what size can I use?  Everyone uses NEMA 23 it seems.  But, like I said, the piece of work that my machine will move will weigh no more than 2 pounds.  Is NEMA 23 too strong for this?  Can I use NEMA 17 or NEMA 14?  Also, what is better for me - unipolar or bipolar?

Now, about the (motor) driver.  Any suggestions on what I can do for this?  As I understand this is the unit that will power the motors (whereas the controller receives and sends signals to control the motors).   Does anybody know of any reasonably priced units or plans to build a simple one?  Also, what do I do for the power supply - are these drivers designed so that you can just plug them into the wall or do I have to use power adapter like the one that I use for my laptop?  Also, does the driver connect directly to the motors (and gives them power) only - or does the driver need to also connect to the controller?  If it does need to connect - and if I buy a controller and driver - do I need to buy them both from the same person so that they will be able to communicate with each other?  Or does everyone build these to a global standard?

Sorry for all the questions, but I thank you in advance for any help.  I have been having a hard time finding a definitive resource that answers all these questions.  Any books you can recommend on industrial automation?

« Last Edit: June 10, 2009, 07:21:21 AM by aljaffee »


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