configuration for simple two motor setup

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14 Apr 2011 11:29 #8895 by frankbatzen
Hi all,

I have started cnc-milling a couple of months ago and have used emc2 from the beginning. What a great piece of software. I can't believe it's free :)
For milling on my XYZ-type Isel FB-2 I got everything working nicely with stepconf. Now I have a project that demands quite a different configuration. I want to run a machine that has two circular "axes". No linear drives. Just two steppers turning independently from each other. I want to be able to program:

stepper 1: turn 200 steps clockwise speed x
stepper 2: turn 100 steps counterclockwise speed y
stepper 2: turn 200 steps clockwise speed z
and so on.

Now that I know my way around a littlebit in EMC2 I would like to use it for this purpose, also. I guess emc2 is heavily underchallenged with such a configuration. But is it even possible to configure EMC2 in such a way? I tried to create a XYZA configuration with stepconf wizard and then tried to eliminate the XYZ part and add another A part as a second circular axis. I could not get the configuration file to work, though. I'm not even sure if this is a good idea.

Alternatively, what software would you use for such a project?

Thank you for your time and effort.
frankbatzen

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14 Apr 2011 19:08 #8912 by andypugh
You could, in theory, produce an AB machine, but by default that would need to have 5 axes.

In practice there is no reason you couldn't use X and Y as rotary axes. (They just won't "wrap" but that probably isn't a problem)

Set up the scales so that 360mm (or 360 inches) is one turn, or just leave scale as 1 and work directly in steps.

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19 Apr 2011 06:29 #9071 by frankbatzen
Thanks alot. That simple.:blush:

How would you go about, if wrapping was necessary?

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19 Apr 2011 09:12 #9072 by andypugh
frankbatzen wrote:

How would you go about, if wrapping was necessary?


It is quite usual to not wrap the rotary axes, so if A = 300 and you issue G0 A0 then the axis will move 300 degrees back to zero and not 60 degrees. This generally makes for fewer surprises.

wiki.linuxcnc.org/cgi-bin/emcinfo.pl?WrappedRotaryAxes

Explains it, though it is not clear from that page whether the feature actually exists.

Looking at
www.linuxcnc.org/docview/html/config_ini_config.html
in the [AXIS] Section the tag is WRAPPED_ROTARY
And it is in version 2.4.6 (This page describes the INI file layout, by the way)

You could try setting TYPE = ANGULAR and WRAPPED_ROTARY = 1 in the [AXIS_0] section and see what happens.

If it doesn't actually work for AXIS_0 and AXIS_1 (coordinates X and Y at the moment, but that hard correspondence will be removed in the future) then you might need to create a machine with..
...
[DISPLAY]
...
COORDINATES = BC
...
[TRAJ]
...
AXES = 5
...

You then need dummy entries for {AXIS_0], {AXIS}1] and {AXIS_2] and set up your rotaries in [AXIS_3] and [AXIS_4]

But, I repeat, wrapped rotaries can catch you out and might not be what you want.

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03 May 2011 10:13 #9550 by frankbatzen
I was away for a while, so finally: Thank you for a great piece of advice. I'm still not sure what I need, but feel enabled to test both options now.

regards,
frankbatzen

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