Steps per inch formula, What I am doing wrong?

[ESjaavik]

Originally posted by Noah I think you guys hold mach 1 mill in a bit too high of respect. Windows is quite capable of dealing with this sort of thing. How is blasting 1.5 Mb/s through a firewire port, getting pics from a USB digital camera, watching a movie, and simultaneously surfing the web any different from pulsing 25 kHz to a parallel port?

Windows isn't capable of dealing with this at all! It's not a realtime OS, and never was.
The big difference is that your firewire peripheral, camera, web and whatever will wait when windows don't want to supply data. When windows gets it's finger out again, the peripheral will continue and be happy. Your stepper motor on the other hand will not wait. It will interpret a lack of pulses as a command to stop immediately. Which is a physical impossibility if the speed is higher than it's startup speed. What happens then is that it stalls out and does so without even reporting back to Mach2 that there is a problem.

Let's say it lost 10mm in Z on it's way up. Mach2 doesn't know, so it believe everything is OK and continue but now everything will be 10mm lower down. If you're lucky it will try to bite too much out of your workpiece. If unlucky it will mill a nice pattern in your table.

I am not familiar with just how mach 1 gets rights to the parallel port during these operations, but I don't think it is that different from a basic printing program. While I have had problems with music and DVD's, I have been able to play games and surf the web while my mill is cutting no with no problems.

You don't think it's much different from a printing program? Then why do you think Artsoft went to great trouble to write a system level task to work underneath windows? Not an easy job to debug I can assure you! We're talking realtime demands here. A realtime task is one that can guarantee that action(s) will be taken at a specific time, not X microseconds later, or earlier for that matter. Those not wishing for trouble will do as HuFlung says. At least you can rest assured that the performance you get from a 500MHz will be consistent when Mach2 is given full control of the machine. If you don't believe us, why not ask Artsoft?

If your concurrent activities on the machine does not involve realtime tasks (created in a similar fashion to Mach2), and does not starve Mach2 user task from processing time to feed the realtime task, then you'll be fine. But are you competent to judge if you fulfill these requirements? Your lack of understanding for these tells me you're not. I don't say this to put you down, as more than 999 out of 1000 PC-users don't know about realtime requirements, so you're in good company.

[balsaman]

What Art has done with Mach 1 and 2, no one has done before. This is why many inexpensive cnc packages that run your motors run in DOS, which is a real time OS. If you want to see windows stepper control before Mach 1 and 2 try Kcam. You will notice exactly what Art has achieved withing the first few seconds.

Eric