interpolation and algorithms of multiple axes was Re: Pulse Gen

Jeff Barlow <jeff@b...> wrote:

> Hi folks,

> I'm starting to recognize a familiar pattern here: people tend to

use

> the tools they are most comfortable with. Presented with the same
> problem, programmers start writing code, hardware designers start
> designing hardware. As luck would have it, I've found myself right

in

> the middle of this sort of muddle many times.
>


> What I think I've learned is that if you don't take the time to get

the

> system partitioning right before you start writing code and

designing

> hardware you end up working way too hard to make something that only
> sort of works. I would say that the stepper code in EMC is a prime
> example of getting this wrong. Mariss's "pulse multiplied" drives

are

> typical of the sort of "bandaid" fix that this sort of poor system
> partitioning leads to.
>



> It seems clear to me that a better partitioning choice is to have

the

> software calculate the pulse rates while the generation of the step
> pulses themselves is best done in hardware. Since a standard PC

does not

> include any appropriate hardware we need the "pulse generating black
> box" that Jon Elson and Mariss, it appears, are both now working on.
>

I could not agree with you more. I do not understand why people are
living with the poor performance of EMC stepper pulses. When the
addition of simple hardware could fix it.

At the risk of being burned at the stake. These are my thoughts on
the efforts of Jon and Mariss.

Mariss's PulseGen circuit is overly complex. 14 IC's per axis is 42
IC's for 3 axis. This is a to much for most people to build at
home. I also am concerned with its max output speed. Mariss says it
is dependent on the clock input to the board but also says 4khz to
8khz are about right. I think we need 13.3khz for a 200ipm rapid
with a 5tpi screw, half step, and 2-1 belt. A fairly typical setup.

If Mariss is talking about building this as a commercial endeavor. I
would feel a little better about it because of its profesional design
and construction. But i would want to know about the speed issue and
what it would cost before we go on. I thought Mariss mentioned
$100.00 per axis but i could not find this statment again. If it is
this much i would say forget it.


Jons circuit is hard to comment on. He tends to be very secretive.
From what i understand you have to sign a non discloser aggreament
to get info on his servo drive. I certainly do not want anything
like that for my use. If he was a large mfg like Mariss it would not
be so bad because you know the support and or product will not dry up
because someone gets tired of supporting it. Jon, what are your
intentions for your step pulse generator for EMC.


What i think we need is something like Mariss's PulseGen circuit.
But we need to have Mariss work with one of you guys that are good
with micro code. I bet Mariss's basic idea with a micro and a few
chips would greatly simplify his design. If this was done as open
source then we could have upgrades and enhancments from multiple
parties. And it would be simple enough to make ourselfs.


Wally K.