Re: [CAD_CAM_EDM_DRO] Re: L297/L298

I was going to build something like one of these
http://www.pminmo.com/l297-8/l297-8.htm
since it looks like a bulletproof version of the standard L297 + L298-based
circuits, as I have on breadboards hooked up to the steppers on my mill. I
think I will build pminmo's version, because it will work, and is just an
upgrade of what I already have, and then later I can swap them out for
something more sophisticated when I need to.

The reprap group is mucking about with a dozen different things. I'm fairly
certain we're going to end up with one PIC16Fxxxx per axis, I don't know
about the drive chips although we're toying with L298s this week. Some of
the PIC16F and PIC18F chips will do usb, which will be handy:
http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=1035&mid=10&lang=en&pageId=74

We're using the SNAP protocol to send orders from the master microcontroller
to each axis, but I think we're going to tweak it a bit. Or toss it.

I haven't built any of these things, or even built a microcontroller
programmer yet, but:
Here's a stepper driver with a PIC16F chip and a UDN2559
http://reprapdoc.voodoo.co.nz/bin/view/Main/StepperDriverWithUDN2559

Some other varients, via searching for "stepper" in
http://reprapdoc.voodoo.co.nz/bin/view/Main/WebIndex

http://reprapdoc.voodoo.co.nz/bin/view/Main/BuildingAStripboardStepperController
http://reprapdoc.voodoo.co.nz/bin/view/Main/StripboardBipolarSlaveStepperController
http://reprapdoc.voodoo.co.nz/bin/view/Main/StripboardBipolarStepperController

I have a question regarding servos versus steppers:
Steppers seem fairly standardized. I can specify a bipolar 1.8 degrees/step
nema 23 mount stepper in a parts listing, and know that a reprap builder can
find one. How standardized are servo motors - is each model unique, or can I
specify a motor with certain characteristics and know that people will be
able to find them? If I'm doing a cnc conversion on a mill, I'm willing to
design my circuits, motor mounts, and shaft adapters around what I can
scrounge. For several thousand user-built machines, it's not clear to me
that I can specify servos.

We're thinking of building linear encoders along each axis, based on photo
etched dots on metal sheet, or something, so who knows what we'll end up
doing?

-Sebastien