Re: servo driver on a chip ?

Try the PIC-Servo SC from JRKerr.

See: http://www.jrkerr.com/boards.html

This one chip and an H-bridge and you are done. As long as you are
willing to live with driving a servo with STEP and DIRECTION. (See
postscripts for overlong explanation.)

This is what I am using on my home made mill - one per axis.

Jim

P.S. Admittedly this "home made mill" is still a work in
progress...so take what I say with a grain of salt. I am stll
learning. (I have finished the three motor control boards and the X-
Y table. Still haven't got a spindle or proper Z axis. That work
thing keeps interferring with my hobbies.)

P.P.S. BTW, JR Kerr Engineering even has a simple open source G-
code interpreter on their web site. It will drive three of these PIC
Servo SC chips. A limited repetoire of G code commands.

Therefore, in order to use these PIC Servo SC chips with any "real"
software (e.g., EMC)...since all these "real" packages will output
is STEP and DIRECTION...he has a feature where the PIC Servo SC
chip will accept STEP and DIRECTION commands...and then turn around
and do the closed loop PID algorithm to actually move the servo.

Pretty silly if you ask me. You are basically making a Servo look
like a stepper. But that is because all the high level machine
control software (e.g., EMC) expects to interface to a Servo using
STEP and DIRECTION. At least without any standard for high level
servo commands (that all Servo driver chips understand directly)
(like perform a co-ordinated three axis move from (x1, y1, z1) to
(x2, y2, z2)) that is what we seem to be stuck with.

But, again, my understanding may be limited. But that is what I
have been able to conclude. It may be that for certain special
Servo drive hardware...(e.g., something common like Gecko
drives)...EMC (and others) know how to "talk" the "special language"
of a Gecko drive...and so can use some HIGHER LEVEL command language
to direct the servo motor controller...and not just STEP and
DIRECTION.

But...I sure concluded that STEP and DIRECTION was the only way I
was going to control my servos...after I bought three sets of PIC
Servo SC chips. I concluded this when I realized that there wasn't
an EMC driver available that understood the high level binary
commands that the PIC Servo SC chips supported. (Just using EMC as
an example, here. Not trying to pick on it. And, anyway, it would
be the chip vendors job to provide such a driver.)

This brings up the thought that perhaps I should write my own EMC
driver for the PIC Servo SC chipset. If I don't want to use the
STEP and DIRECTION interface option. Yeah. That is true. But then
I would have to find the time for THAT project, too. :-)

Anyone care to jump in an correct me...on any of the points in my
postscripts?

As I said, I am still learning.

And I must apologize for hijacking the thread....with my overlong
postscripts.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dennis Schmitz"
> <denschmitz@> wrote:
> >
> > It might be totally different inside, but it still performs the

same

> > function, taking command input and controlling something based

on it.

>
>
> I think the general concept of a close loop would fit both. the
> difference being the type of sensors. Although I don't think

there is

> a specific requirement for any type of sensor, the R/C servos would
> not require anything that might be unlimited. whereas a
> MotionControl Servo certainly would find it hard to use a fixed

range

> device like a pot. The main difference being that the R/C unit

might

> not have to make a full revolution, whereas the MC applicion offen

has

> many hundreds of revolutions.
>
> But the concept of monitoring the error and correcting for that

would

> be common to both.
>
>
> > It's just a different command format. A servo could just as

easily

> > take a command as an analog signal input or a byte code, or even

a

> > complex command sequence specifying position, speed,

acceleration, and

> > timing profile for the movement.
> >
> > This is probably out of context here, though (although not

necessarily

> > off-topic). This industry is used to the step/direction command
> > format, but that's certainly not the only way to get things done

(or

> > the best one). With a rich command format, you can reduce the

load on

> > the main computer as well as receive fault codes from the servos.
>
> I think the whole concept of a serial command vs. parrallel

commands

> is being used in more than a few devices.
>
> The idea is to be able to use a driver with something like Mach3

that

> does output a step and direction signal.
>
> As I understand, allegro and Sanken as well as some others put
> complete circutis on a chip. Allegro puts a stepper driver on a

chip.

>
> At some point someone should put a quadrature interface on a chip

as

> well as a motor controller to make a single chip device that would

run

> the items necessary to make a MC servo on a chip.
>
> MicroChip does have an application bulletin that gives all the

details

> to put all the bits together to make a stepper drive on a PIC.
>
> And, putting the whole thing in software would be fine as well.
>
> So, I guess that is the real question. Is there a means of putting
> together a motion control servo driver ?
>
> Dave
>