Re: 4th Axis Concept (long)

Hi Alan -

Its a 16F877, clocked at 20 MHz, programmed almost entirely in "C".
Been there, done that with assembler in past lives - didn't fancy
learning yet another way of programming on my hands and knees!

The "C" compiler is a bit memory hungry, but very quick to develop
stuff - the dev system runs under Windoze & includes a (software)
simulation environment that can also emulate the common PIC
peripherals - LCDs, keypads, digital I/O,...great stuff. You can do
much of the testing without going near a PIC chip. The compiler is
marketed by FED:

http://www.fored.co.uk/

The early versions were a bit buggy - they hadn't quite sussed the
memory paging on the 16F877 & I found some of the bugs for them - but
the current version (V7.0 or thereabouts) seems pretty solid.
Handles code generation for a wide range of PIC devices. They do a
good programmer & dev board too.

My controller does a simple (linear) accel/decel on all moves - one
start/max speed for jog & another start/max speed for the other 2
modes. With a step/direction chip like the L297, the stepper drive
code is pretty trivial. The hard bit (as with most computer-based
projects) is getting a sensible user interface sorted out; also doing
the math to translate angular positions to/from motor steps is a
pain. Most of that is done fixed point in 32-bit variables - a
nightmare constructing the expressions to guarantee that you don't
get overflow/underflow.

Thanks for the beta offer - will bear it in mind. First problem is
to get some proper hardware together - the prototype is a breadboard
job at the moment. There's a bit of work to do to get it into a
sensible & buildable form.

Regards,
Tony

--- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> Hi Tony,
>
> Sounds great! Which PIC are you using? All .ASM, or some 'C'? Do
you
> do accel/decel? I've been wanting to get stepper code into a PIC!
>
> Alan KM6VV
> P.S. I've got a CNC rotary table, PIC's, etc. if you want someone
to
> Beta.
>
> tony@j... wrote:
> >
> > --- In CAD_CAM_EDM_DRO@y..., Chris L <datac@l...> wrote:
> > > Sheez, if this is this basic why is no one marketing such a
little
> > beast? You know
> > > what they get for a small powered Indexer.......
> >
> > Talking of small powered indexers, I have a working prototype of a
> > small powered indexer, based on a PIC microcontroller and a
bipolar
> > drive (L297/298), intended to drive a rotary table or dividing
head
> > fitted with a 400 half-steps per rev stepper motor. Brief features
> > list (at present):
> >
> > - 2-line by 16-character LCD display and 16-key membrane keypad;
> > - Setup parameters stored in Non Volatile RAM - remembers the
> > settings from last time it was powered on;
> > - Will cater for any worm/drive ratio between 1:1 and 99:1;
> > - Adjustable initial/max feedrates and jog rates, from dead slow
to
> > around 60 degrees/s with a 72:1 worm drive (e.g., the Sherline
rotary
> > table);
> > - Adjustable ramp rate;
> > - Software-based backlash compensation;
> > - Bipolar chopper drive - usual L298 spec (2 amps/phase), with
> > chopping current settable via software;
> > - "Jog Mode" gives CW/CCW jog in increments of 1/100th, 1/10th, 1
and
> > 10 degrees, with display of desired and actual angular position
to 3
> > decimal places (where the desired position cannot be achieved,
actual
> > position is within 1/2 step of the desired position);
> > - "Division Mode" allows operator to set the number of divisions
> > between 1 and 999. Table can be driven CW and CCW one division at
a
> > time - display shows current division number, plus actual angular
> > position in range 0 - 359.999 degrees;
> > - "E-Stop" key halts any move immediately, but the current/desired
> > angular position is remembered - hence, position is not lost on E
> > Stop.
> > - "Degrees Mode" - similar to Division Mode, but the move is
> > specified in degrees to 3 DP;
> > - Motor connector is plug-compatible with Taig's CNC equipment (6-
pin
> > DIN plug);
> > - Breakout connector provides for external control of CW/CCW moves
> > and E-Stop, and also provides step/direction outputs if needed to
> > control a higher power driver stage.
> >
> > I'm currently working on getting the board into production - watch
> > this space.
> >
> > Regards,
> > Tony