4 Axes Machine Questions

Todd Zuercher wrote:

I tried it and received the error

Debug file information:
core_stepper.hal:32: Pin 'axis.2.motor-pos-cmd' was already linked to signal 'Zpos-cmd'
7643

Ah, yes.

In that case, you probably need to use "linkps"

halcmd unlinkp axis.3.motor-pos-cmd
halcmd linkps axis.3.motor-pos-cmd Zpos-cmd

And

halcmd unlinkp axis.3.motor-pos-cmd
halcmd linkps axis.3.motor-pos-cmd Apos-cmd

(except, of course, that I just told you to delsig Apos-cmd, so you will need to restart the config to recreate it)

I am shooting from the hip here, I have never tried this.

Did you "short circuit" the stepgen feedback?

(I should have said, the feedback from the stepgen just reports that the pulse generator can keep up with the commanded speed, so is semi-optional)

If you are talking about changing this line

net Apos-fb stepgen.3.position-fb => axis.3.motor-pos-fb

to

net Zpos-fb stepgen.2.position-fb => axis.3.motor-pos-fb

Yes I tried that. and it had no effect.

But I did notice that while I have the net Apos-cmd axis.3.motor-pos-cmd => stepgen.3.position-cmd line short circuited, when I try to jog it does move the A axis, just a tiny amount before it gives the joint 3 error. Is there a way to cut this off further upstream, so that what ever is seeing the error sees this as a commanded movement instead of an error?

Todd Zuercher wrote:

If you are talking about changing this line

net Apos-fb stepgen.3.position-fb => axis.3.motor-pos-fb

to

net Zpos-fb stepgen.2.position-fb => axis.3.motor-pos-fb

No, that's not really what I had in mind.

The feedback loops shouldn't change and can be: (check the pin names, I am at work)

net Z-fb axis.2.motor-pos-fb <= stepgen.2.motor-pos-fb
net A-cmd axis.3.motor-pos-cmd => axis.3.motor-pos-fb # Short circuit

The Z command stays the same at all times.
net Z-cmd axis.2.motor-pos-cmd => stepgen.2.position

Now, to link motor 3 to the Z axis:

unlinkp axis.3.motor-pos-cmd
net Z-cmd axis.3.motor-pos-cmd

And to make it follow the A-word in the G-code

unlinkp axis.3.motor-pos-cmd
net A-cmd axis.3.motor-pos-cmd

(Again, all untried and untested)

Now to dredge up an old thread.

I think I've finally mostly solved this! :woohoo:

I made two custom M-codes (M122 and M123) that temporarily slave the movement of the W axis to the Z.

It works with both a stepper config (in simulation at least) and I have it running on a servo machine as well.

One bug that I still have to squash though is that while slaved the following error of the W isn't monitored. No big deal for a stepper system, but a little scary with a servo. I have some ideas but have not taken the time to implement them yet.

Here is the stepper config as an example for others to look at. (The M-code files need to be located in the right place to work as well.)

Ok, I think I have a feedback system in place for my servo configuration.

What I did is to use sum2 to add (subtract actually) the axis.8.motor-pos-cmd and the PID error for the W axis. Feeding that to the mux2 that short circuits the W feedback while operating in ZZ mode.

It seems to work ok now, but the very first time I started the config, it did a false runaway on the W axis when I switched to ZZ mode (numbers on the DRO were moving but the motor wasn't). After a restarting Linuxcnc it has behaved fine. (Fingers crossed)

Attached is the servo config.