Newbie- cnc dmx bridging?

[assimilat]

I hope im posting this in the right place...I've searched the forums and google to no avail to find a solution to this...perhaps its just my google-fu though.

Anyways I work in the nightclub industry as a lighting / sound technician and I have a respectable stash of broken lights that all have at least 4 stepper motors in them...I also have several USB DMX interfaces http://en.wikipedia.org/wiki/DMX512 . It would be no problem for me to put together a system that uses 40+ stepper motors simultaneously out of the hardware and software systems I have and know how to use. Now what im wondering is if there is a way to get any cnc app to talk to a usb dmx interface with the main intent of just using 3 axis's for a temporary PCB mill so I can cut out some boards that would be a bit more standard. I know I can buy them cheaply but where is the fun in that ;-) right?

I was also wondering because of dmx's chainable/addressable nature could/have its principles been used in cnc controller design? So you would have one usb interface connected to your pc and then you have multiple devices chained to that controller (i.e. a mill chained to a lathe chained to a plasma cutter or multiple mills). I was wondering that because standard DMX has 512 channels that can be used simultaneously. That is 512 potential stepper motors/led's/limit switches that could be connected. So if i wanted to for instance run 4x 3-axis pcb mills at the same time I could address them as 1,4,7,10. and send different values to each group of 3. Or if i wanted 2 of the mills to cut the same board and 2 of them to mill unique boards I could just address the first 2 on address 1 so they would get the same signal then the other two on address 4 and 7.

I know im probably making a lot of leaps here but in my head it seems very doable to the point of me wondering if it has already been done.

Here are some links /w dmx info...

Here is an example of a diy 2 axis DMX stepper controller(this site has a lot of other cool diy dmx stuff that would be interesting to use in conjunction /w cnc's like matrix led controls for readouts and relay packs:
http://www.hoelscher-hi.de/hendrik/english/stepper.htm

This site has a lot of really random tech info about dmx:
http://members.westnet.com.au/rowanmac/opendmx.html

Here is a USB DMX Interface example:
http://usbdmx.com/

This is the software I use for DMX control:
http://users.telenet.be/freestylerdmx/
and
http://vvvv.org

THANKS!!!
-Andrew

[assimilat]

Sorry to drag up an old thread but I had an update on this if anyone cares...I was actually able to get Mach 3 scripted to output DMX....It took way longer than I thought and it wasnt fun but it did work. It actually worked rather well on the software side of things anyways. There was one tiny oversight though that made the whole project crash and burn. A typical DMX light's motor controllers (or the ones I have anyways) are limited to a certain number of revolutions. (in hindsight i want to slap myself)...i.e. one of these wont just continuously spin 360 degrees forever due to their being wire harnesses that would twist and the like...That and a mirror scanner's mirror is limited to like 90 degrees of motion because it only points light one way...

So after much headache the project has turned into me salvaging what I can from my script work and the Light controllers (i.e. stepper IC's and such). If anyone is interested I can post my scripts to make Mach 3 work with DMX...They are pretty useless for motor controllers due to the above mentioned limitations. But they may yet be useful if you want to control DMX relay packs, any sort of DMX indicator lights or DMX dimmers etc from Mach 3.

Now on to my scrapping...After pulling the boards and studying the control circuits ive found that they all use ULN2803A Darlington drivers to push most of their motors...with the exception of a few that use a New Japan Radio NJM3771D2 stepper driver IC. I have a fair supply of both...enough to have some fun with i'd think (24x ULN2803A's and 8x NJM3771D2's). Since I started this project I have read a great deal on control using the Darlington drivers and I am pretty comfortable with them so far(i.e. I can control motors /w them) but where im getting hung up is with the NJM3771D2. The datasheet for it is REALLY vague but from what I can gather from it and the application examples it has a DAC that they make specifically for that IC(NJU39610) to use for microstepping which was not included on the light controller boards(nor is any other DAC that is interfaced by the stepper circuit).

What im wondering is.
(A)Do i need that exact DAC if I want to microstep with that driver IC? And what is the DAC doing anyways?

(B) If I do then why was it not included on the DMX light boards? What is the advantage of using a NJM3771 instead of a ULN2803? Im wondering because the NJM3771 is a much more expensive IC than the ULN and im just trying to understand why it would have been a better choice for the application it was used in.

(C)Im trying to figure out if I can interface the NJM3771's in the same manner I do with the ULN2803's via a parallel connection. I know it is possible in some regard but the datasheets only mention microcontroller interfacing which is what they were connected to in the lights. (8051's to be more exact). If I can run them in a similar fashion and I can achieve microstepping without using a DAC or even a more standard DAC I already have i'll be one happy camper...Heck if I can get away with just grabbing some NJU39610 DACs from digikey and interface directly /w those to the NJM3771 via parallel i'll still be gold....If not then i'll just save the NJM's for an AVR project or something.



Sorry for the long post...Im just trying to learn here and I wanted to see if I could build something useful using some of the busted hardware around my shop while forcing me to read a lot more than if I were to just buy a ready made solution. I also just wanted to give anyone a heads up if they decide to go the same route I did trying to make a dmx stepper controller operate a CNC device. Hopefully this has enough DMX / Stepper keywords to show up in a search so they dont make the same idiotic mistake I did. And if anyone wants my Mach3/DMX script for anything just hit a reply and i'll post a link...Its not doing me any good right now but it does all the parsing just fine and may be useful for something...

If anyone can give me some info or point me in the right direction on the stepper driver IC issues I would be very greatful! And are there any good books/websites about stepper control/driver design implementation that im missing? Does anybody know of a good general reference book for digital logic circuits? Im reading this right now

Stepping Motors: A Guide to Theory and Practice

Stepping Motors: A Guide to Theory and Practice

and watching the MIT OpenCourseWare (http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/video-lectures/) ((wouldnt let me link that for some reason)) circuit design/analysis lectures right now too which are beyond awesome but I obviously cant ask them questions...Other than that all I have been studying are the resources on TI's website (which have been very helpful)well that and you guys!

I hope I could help at least one person...and I hope someone helps me

Thanks!
Andrew

[vger]

Interesting... I had not heard of DMX512 specificly, but figured something like that existed. The one issue I can see with trying to control a CNC machine with this method is timing. Since the individual nodes are addressable on a single control link, wouldn't that make simultanious starts impossible? Seems you would have to address and command one motor/controller then the next and so on. If you wanted a 2 axis machine to do a 45 degree move, you would command the X axis to move, then the Y axis. Wouldn't there be a delay in the second axis starting it's move?

Anyway... the DAC's I would assume the DAC's contol the current in the individual windings via the H bridge chopper circuits in the NJM's to achieve the microstepping. Trying to so the same with the ULN2803A's would be really difficult with out adding analog controlled chopper circuits to each input.

You should be able to use the NJM's phase inputs to run them, but it would not be step/direction control, it would be quadrature sine/cos control.

Best of luck