Bridging EMC and Router

You might start with the EMC manuals.

John

atmegaist wrote:

I'm curious to see what I can do as far as constructing a router and am having some trouble understanding what it is that EMC is actually sending through the parallel port.

That rather depends on how you set up the system:

1) Possibly the most common, is step and direction signals on 2 parallel port pins per axis, to external drives which handle the power electronics, current limiting and step pattern generation. One pin goes high for one direction and low for the other, and the second pin pulses every time a motor step is needed to keep the motor in the correct position.

2) Rather less common: EMC2 generates the step patten on 4 parallel port pins, this goes to simple power electronics (as simple as a set of power transistors) and drives the motor sem-directly. This mode could in fact drive extra-tiny motors with no extra electronics. This isn't a very good system.

3) The parallel port can be used as a communications port to an external step generator. (Pico PPMC, Mesa 7i43, Motenc or Pluto(just don't)). EMC2 sends a step rate and the external hardware does it. This gives much higher step rates, and frees up a lot of CPU. You still need external step/direction drives though both Mesa and Pico sell hardware that connects directly to the interface card.

4) You can not use steppers at all. You could use servo motors. The parallel port would have a PWM signal to control motor speed (or torque, or voltage, or currrent depending on the drive hardware) and a direction pin (optional, you can use biased PWM but that has certain "issues"). You then need at least 2 input pins on the p-port for an encoder on the motor so close the feedback loop.

5) As 4, but with a Pico or Mesa card generating the PWM with amplitude commands sent digitally. You can use separate PWM and direction drives, or integrated drives from the manufacturer.

6) As 5, but with the interface communicating digitally to the drive (defining PWM as analogue, for the moment)

7) Skip the Parallel port and fit a PCI card.

8) Almost anything else you can imagine. EMC2 is extremely flexible, and if you need something special, it is all open-source so you can write your own bits.

www.mesanet.com
www.pico-systems.com/motion.html

What sort of stepper driver are you using?
If it is a step/dir type then all you need is wires.

if you are trying to drive the stepper semi-directly, then you can drive a unipolar stepper motor like this using a ULN2003
www.mycncuk.com/forums/showthread.php/20...r-motor-with-ULN2003

In that case you would use the EMC2 stepgen component in Mode 9
www.linuxcnc.org/docview/html/man/man9/stepgen.9.html

However, this is not a very efficient way to drive steppers, you will get much better performance in Bipolar mode with a current-limiting chopper driver, running at much higher than "rated" voltage. In this setup the drive limits the motor current, not the motor DC resistance. You then use 10x the DC voltage and get about 10x the speed/torque.

I am still not at all clear what drive hardware you have?

atmegaist wrote:

I actually don't have a stepper driver (I thought that was what I would ultimately build and LinuxCNC would act as the controller... Is my thinking correct on this?)

Indeed, that is exactly what you would do.
You might want to consider buying rather than making a driver board, there are many on eBay as direct imports from China for rather less than you can build them for.
As a random example: cgi.ebay.co.uk/3-Axis-CNC-Stepper-Motor-...TB6560-/250733402363
Try a search for "CNC Stepper" on your own local version.

One more possibly stupid question: can all unipolar stepper motors be configured to operate in bipolar mode? I understand how to set them up as such but was curious to know if there were any certain exceptions.

I don't know of any exceptions, nor can I imagine how there could be, but I could be overlooking something.

Keep us posted on your progress building a drive... it could be interesting.

John