RE: [CAD_CAM_EDM_DRO] Re: VEX CNC

We have VEX motors too, not just servos, so we can do multiple revs. We
also have optical encoders - not quadrature, and 4 degree resolution.

Curious about the steppers. We have several salvage(d)able printers with
small steppers, but thought we needed different stuff to run them. Would be
curious about running small steppers with VEX controller. Also have DC
motors with encoders out of some printers too.

Will look up the algorithm - thanks!!
C

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Ron Ginger
Sent: Friday, September 12, 2008 6:38 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: VEX CNC

>> Posted by: "Chuck Merja" chuckm@3rivers. <mailto:chuckm%403rivers.net>

net ebiz_59

> Date: Thu Sep 11, 2008 7:46 am ((PDT))
>
> Thanks for the comments. It looks like I am trying to fit a round peg in a
> square hole, maybe?? I'm interested in VEX stuff because we have it and we
> have a little expertise in programming it. The controller has a Microchip
> PICmicroR PIC18F8520 and uses PIC C, and we use EasyC to do the

programming.

>
>
> Am I getting from you that the controller and C might not fit CNC use? I
> didn't see a way to interpret shapes, especially without a fair amount of
> programming, which isn't the goal. The goal was to find yet another use

for

> use the VEX platforms we have (or understand why they aren't the best fit)

-

> I just added the part in parentheses, cuz that looks to be where we are
> headed:o))
>

>VEX would be an excellent choice for making something like a pen

plotter. The controller with it is more than capable of the job, much
more so than a PicAXE chip.

I think the issue is that a servo, the kind in VEX kits, are not very
accurate for position control. They have a short arm that only operates
over less than 180 degrees. They are also essentially analog devices, as
they are controlled by a pulse width.

A couple small steppers, even those salvaged out of old floppy drives
should work fine, and should be easy to interface to the VEX controller.

It will be a programming project. The mechanics are nearly trivial,
programming it will be the trick. To draw circle you need to look up
Bresenhams algorithm. It converts the circle into a series of short X
and Y steps.

ron ginger



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