Re: [CAD_CAM_EDM_DRO] Re: Interface. Gauging interest.

Mariss,

Could you talk a little bit more about the effects of jitter?
Clearly, this is a concern of mine with this FTDI USB interface thing
I'm working on.

Assuming that I can maintain the stream of bytes out to the stepper
controllers (Allegro SLA7062M chips on the HobbyCNC board), I have 6.5us
resolution. I'm not too worried about the really slow step rates, since
6.5us resolution on a 100Hz (10000us) step rate is negligible.

But, at the maximal step rates, I could theoretically be alternating
between 13.0us and 19.5us (worst case, highest step rate).

Is there a way to calculate what my loss of torque would be for this
case? Or, is this something that I just have to measure (maybe by
direct comparison with a high res timing pulse source??)?

To be honest, I'm not quite sure how I would measure the effective
torque in this case, so any hints you have there would be appreciated,
too...

Thanks!
Mike

Mariss Freimanis wrote:

> I try real hard not to promote our gadgets when a different solution
> is a better fit for a given application. This is a good example.
>
> A parallel port is an execellent choice for moderate performance
> applications; it is in fact the only $0 solution I'm aware of.:-)
>
> Mach3 outputs acceptable timing jitter pulses to 45kHz, in DOS,
> CNCPro outputs excellent timing jitter pulses to well over 200kHz.
> There are plenty other parallel-port CNC programs but I have taken
> timing data on only the two I mentioned.
>
> This is adequate for over 80% of applications. A solution that has
> uneeded performance is not attractive if it costs more. A solution
> that offers equal or worse performance isn't attractive if it costs
> more.
>
> The parallel port will be obsolete in time. Until then it truly is a
> zero hardware cost solution that is hard to beat.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jack Hudler" <yahoo@...>
> wrote:
>
>>
>>You already use external hardware, namely; motor drivers, encoders,
>
> and perhaps
>
>>relay boards. What's one more device?
>>
>>Using a parallel port is a senseless, jittery, amateurish and
>
> dangerous method
>
>>of motion control. I could understand this in the early years
>
> (<95), but not now
>
>>and besides the parallel port is slowly becoming extinct.
>>
>>Mariss, you yourself already sell the G-Rex 101 product that
>
> eliminates the need
>
>>for a parallel port. Why not make a 3 axis version for 1/3 less
>
> (though I doubt
>
>>you could get 1/3 less on removing 2 connectors and some buffer
>
> chips).
>
>>Just venting,
>>Jack
>>
>>-----Original Message-----
>>From: CAD_CAM_EDM_DRO@yahoogroups.com
>
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com]
>
>>On Behalf Of Mariss Freimanis
>>Sent: Monday, May 15, 2006 1:07 PM
>>To: CAD_CAM_EDM_DRO@yahoogroups.com
>>Subject: [CAD_CAM_EDM_DRO] Re: Interface. Gauging interest.
>>
>>Many successful and popular CNC programs use the parallel port.
>>Repugnant though it may be, what other port would you suggest be
>
> used
>
>>instead that requires NO external hardware?
>>
>>Mariss
>>
>
>
>
>
>
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