Mesa card and absolute encoders.

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08 Aug 2019 06:43 #141656 by Roiki
I'm designing a 6 axis robot with the intent of using absolute encoders on all axis and am wondering what type of absolute encoders can be interfaced to mesa cards and Linuxcnc? From bit of googling I gather that SSI encoders can be used but can SPI or RS-485 encoders?. I'm thinking of using the following encoders:
https://ams.com/as5048ahttps://ams.com/as5048a
CUI AMT-21 series
CUI AMT-23 series

And how would they be interfaced? Through a 7i44 board? Or can the 485 encoders be used with just the RS-485 interface?
Im thinking of using the 7i93+7i44+7i47 combo.

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08 Aug 2019 15:07 #141686 by tommylight
You should confirm this before a decision, but i do not think you can use RS485, i do not know if you can use SPI, i am sure you can use some SSI.
I did use SSI on a retrofit and it worked perfectly, using a Mesa 7i74.
Someone else with more experience regarding this might be more useful.

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08 Aug 2019 15:32 #141688 by PCW
There's no direct support for SPI encoders in HM2
SPI is not a great long distance protocol, I'm pretty sure those
SPI interfaced encoders are intended for applications where
the SPI link communicates with a local (inches away) microprocessor
The following user(s) said Thank You: Roiki

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09 Aug 2019 09:48 #141730 by Roiki
It seems I'll go the SSI encoder route then. Would it be possible to use a different ethernet card for the encoders only? Something like a 7i94 for the encoders and another board for step generation. Id like to keep the cabling to a sensible level.?

Also I've used those spi encoders before and they do work fine with 2m cabling. You can also extend spi to a degree with lvds.

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10 Aug 2019 19:10 #141882 by PCW
You can use multiple Mesa Ethernet cards (up to 4 currently) with LinuxCNC
You would want a fairly fast host CPU to use multiple cards

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12 Aug 2019 07:11 #141951 by Roiki
How fast are we talking about? I've been thinking about using something like a RPI4 or intel NUC(or other small machine) to run Linuxcnc since i don't need graphics performance to drive the UI.

Mostly Linuxcnc would take care of the motor control loop and maybe some light kinematics down the line(I already have ROS for complex planning) and to make and run programs.

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12 Aug 2019 18:40 #141980 by PCW
I would probably say I3 or better

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