Re: 5-axis machine controller

["D.F.S." <dfs-at-xmission.com>]

> 
> 
> Hi Robert,
> I have a phase drive system running with EMC. The electronics package is
> from TMG (The Motion Group) and is a small box with power supply and 3 2A
> stepper drivers. In the cvs code, I wrote an alternate phase drive
> subroutine that could be used to drive unipolar stepper phases through a
> logic level fet and current limiting resistor. The code I wrote is very
> simple and can be changed from 2 outputs/motor to 4 outputs/motor quite
> easily. The output bit patterns are looked up in table. You could also used
> a decoder driver chip to convert the 2 bits/phase to the 4 bits of logic
> level fet drive you are considering. You may want to have a look at the code
> in emcmot.c around line 3500. Let me know if you need some help modifying
> the emc code. I am starting on a drive system for a new machine and need to
> run 4 unipolar steppers at 4.7 amps/phase. I am still looking for the
> easiest/cheapest way to get the job done. I have not decided if I will use
> the direct phase drive method with resistors or try something that has a
> switched mode current source for better efficiency.

Well, I bought a batch of misc stuff maybe a year ago when there was talk of
doing a design here for an open-source type design for a driver board.

Some of the things I got were 3 amp outut op-amps, 3, 5 & 10 amp Fets, 
Bi-polar? 'Regular old' 10 amp Metal Can Transistors, Opto-isolators, 
a slew of regular old op-amps and a ton of LEDs, I already have ~50 
thousand Misc TTL parts...
The last time this came up after lots of arguments the project appeared to
disappear although it looks like one LPT interface may have been built...


In any event, could you elaborate on the "Fet & Resistor" scheme please?

Where and why are you using the resistors?

The FETs I have are not logic level, but that should be easy enough to
work around I presume.

Marc