Re: [CAD_CAM_EDM_DRO] Re: IMService releases ncPOD system

Hi Guys:

Just some clarification...

>http://groups.yahoo.com/group/mach1mach2cnc/message/73372
>
>Quite clearly Art considered it in full release on April 25.
>Changed his mind by 8th May

My fault, Im a web screwup. The site has had a few troubles due to growth,
and we seem to be getting files
constantly overwritten with older ones. Site seems to grow too fast.. ,
anyway, the Pod is considered now to
be in release. Very few problems reported, and mainly in systems with slow
USB timing. Almost all functionallity
that can be done is now done. I only need to finialise the probing checks
and see how that works, hopefully
in the next couple weeks. But in general, the pod seems to work quite well,
any remaining bugs will be repaired
as they get reported. My fault the indication seems to be changing though..
Ill fix up the link..

>>IMO - The Ncpod has some limitations which should be made clear to any
>>prospective users.
>>Each port is only rated at 20mA.
>>Only one axis can be jogged at a time (multiple axis moves are fine
>>under code). In truth - this hasn't caused me any problem.
>>PWM output is 75kHz, it's output voltage is only 3.5V and it will not
>>work with much of the existing hardware out there without modification
>>or additional hardware.
>>Index pulse input doesn't work with Mach due to latency problems and is
>>not supported currently. Whether it ever will be would be guessing.
>>It will ONLY work reliably with USB 2.0 ports - even having legacy USB
>>support turned on in the PC bios will often cause "The pod has ceased to
>>respond". This particular problem has caused more support queries than
>>any other despite the information being posted numerous times.

Very true. As with any external device, the released ones as well as ones
to be released,
I recommend checking carefully as to limitations. Many thing external
devices are the most
efficient way of pulseing since load is removed from the computer, in truth,
its much more
complex than that. Visceral feelings aside, each device will have its own
limitations. I can control
a printer port to 28us granularity, remote devices can rarely manage that in
terms of pulse to
pulse control. The amount of data that can be transfered is a limitation in
3d codeing. Doing a
mould or other tight 3d job often makes it necessary to have thousand or
tens of thousands of
small .001 movements, remote devices can rarley take data fast enough not to
have some limitation
in speed. Obviously if every move is .001 and you need to do 300IPM, then
you need 5000 commands
per second to transfer to the device. The Pod has a limit of about 600 per
second , while the G100
is limited to 50 - 60, the printer port to 5000 or so per second. So as you
can see , various limitations
exist simply due to transfer speeds. (The G100 is being looked at to
increase its bandwidth as I type this..).

My point is that each device will always have its own limitations. The
galil I fill at 4ms intervals of command
length, the G100 is 1ms, the ncPod is 800us , the G100 has lots of IO and
encoders, the pod does not. etc..
etc.. etc..

Since documentation is sparse on most of these types of issues, its always
best to ask someone with one,
and get their feedback. The ncPod though, is working very well going by
reports, as is the G100, they simply have
differing capabilities..


one note:

>>PWM output is 75kHz, it's output voltage is only 3.5V and it will not
>>work with much of the existing hardware out there without modification

I think thats an average voltage being measured, Id be surprised if the
chip is actually a 3.5 volt one. ( Steve, are you sure
this is true on a scope? I think the PWM, always being on, makes it average
to 3.5 volts on most meters, I havent scoped it
as yet, ...should I? :-) , but you could be right on modification, 75Khz is
pretty fast pwm..maybe we shoudl ask Carl to lower it
to 100hz or something..)

Thanks,
Art
www.artofcnc.ca