"Smarter" motor driver support ?

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21 Mar 2010 12:35 #2395 by robots
I have just come across the EMC, and to me it looks that every HW that is supported is dumb - as in simple IO. Most calculations (PID, etc) are done in software. If i understand correctly, this is the reason why RTOS capabilities are needed.

Right now I'm in the middle of construction of controller that is able to drive one HSM motor with encoder, either in position mode, or velocity mode. Connected to the outer world with CAN bus. Having the PID, homing capability, etc on board would offload the main computer a lot.

Are such controllers supported? Where EMC would just send position to the board, and would get feedback in some time (e.g 1ms?)
If not, how much would need to be changed in the current source ?

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21 Mar 2010 13:41 #2396 by BigJohnT
EMC is a smart controller and uses dumb hardware.

John

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21 Mar 2010 13:49 #2397 by robots
Replied by robots on topic Re:
Any plans of adding support for such HW? Maybe having architecture, where one can choose backend - smart SW dumb HW or less smart SW, smarter HW ?

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21 Mar 2010 14:13 #2398 by BigJohnT
Replied by BigJohnT on topic Re:
You might ask on the #emc-devel IRC channel. I doubt that there is any plans to do so, but you can change the source code to suit your needs.

John

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21 Mar 2010 15:54 #2399 by PCW
Replied by PCW on topic Re:
My $.02

I think the basic issue with buffered or "smart" drives is that for EMC not to be limited by the hardwares capabilities
EMC needs real time control. Once you have the locus of real time control in the PC, smart hardware mainly gets in the way.
As John T. said, EMC is a smart controller.

Because all of the "smarts: are in EMC, from a simple parallel port driven step motor system to a dual feedback 5 axis servo system,
all of EMCs basic capabilites are retained, independent of the hardware. If a new feature is added to EMC, it is available to
all users regardless of hardware.

Consider rigid tapping, probing, homing or threading: all of these need real time inputs to motion control.
While its possible that external hardware to support these operations, you now have a much more complicated system with multiple
centers of control, and communication delays between these centers.

Even a drive with its own PID loop has its disadvantages: Instead of using the standard EMC tools for tuning (and having access to all internal variables)
you must now use a separate non-integrated utility to tune the drives.

If your drive can work with real time velocity commands and return position every mS. that should work with EMC
(though a real time driver that supported the CAN interface hardware would need to be written)

heres a link with some more information on EMCs hardware design model:

wiki.linuxcnc.org/emcinfo.pl?Emc2HardwareDesign

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21 Mar 2010 16:55 #2400 by robots
Replied by robots on topic Re:
Thanks for input

I was thinking of using EMC on something other than x86 arch, probably ARM or PPC. So there is no parport, nor pci.

My drive's HW is ready, and the SW is on the way. I'm just gathering some information on what features it does need. I have mostly been inspired by "EPOS 24/5" controller that we used in one of our projects.

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