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MagIO2 schrieb: All boards that connect via USB have their own mikrocontroller which generate the singnals that the PC generates in a LPT setup by itself. The point with the LPT solution is, that on a PC a bunch of software is running. Even if you did not start a single program yet, there are tons of drivers and stuff running in the background. And you have another ton of hardware interrupts which occur. All this makes it impossible to generate signals with a precise timing. The question is: Is the quality of the signals still good enough for controlling a CNC.
Even older machines than your i5 should be able to handle a CNC, but the faster the better the quality of the signals. What you really should avoid is running other software during a cutting job. This can kill signal quality.
The benefit of the mikrocontroller solution is that it has only 2 things to do: communicate with the PC and control the CNC. The signal quality is higher (still not precise) and can be guaranteed to be the same during the whole job (well except there is a communication problem between PC and uC ;o) On the other hand, sending some kB of g-code is not that hard for the PC and you can run many other programs while running a cutting job.
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OpaHoppenstedt schrieb:
LinuxCNC is not as easy to set up as the Windows based stuff. First it is only available for Linux,
second it will not run smoothly on any PC. The problem here again are the real time requirements
as the PC directly generates the step pulses for the stepper motors. Surprisingly a state of the art
motherboard in many cases does not work well and there is a lot of discussion in the LinixCNC
community about latency.
(Side note: in principle the setup is just the same as with Mach3, a PC directly controlling the router via
an LPT port, but with Linux instead of Windows. I haven't heard about latency problems running Mach3.
Could it be that Windows is much more a real-time operating system than Linux?)
What does that latency stuff mean? The Stepcraft moves 2mm per revolution of the stepper motors doing
400 steps. That are 200 steps per millimeter. If you want to move 10mm per second, which is not very fast,
the pulse frequency is 2000Hz. The PC therefore generates a square wave, but this is done in software by
toggling a pin on the parallel port. Now the PC has lots of other things to do at the same time, and some
of them may not always be immediately interruptible. This is called latency. The result is that the
distance from one pulse to the next varies a tiny little bit. Who cares? The stepper motor does!
When you go from the USB controller to LinuxCNC the sound of the machine changes.
Cheapest most reliable controller combination that is compatible with windows and can be stable out of box on almost any windows PC - is the UC100 / UCCNC combination. In our opinionOpaHoppenstedt schrieb: in a proprietary
environment.
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OpaHoppenstedt schrieb: I totally agree that any pulse train generated with hardware support, and this can be a dedicated microcontroller chip, will be much more accurate than a software loop. I just don't see the problem that needs to be solved. My little Atom based LinuxCNC box can run another router with rapids in excess of 100 mm/s at 0.00625 mm/step. That is about 16000 steps per second and I haven't noticed any lost steps. This is way beyond the 30mm/s limit of a Stepcraft. I am completely happy with the LinuxCNC performance once I had found the right board.
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