Schaublin 125-CNC retrofit.

I am thinking it is best to remove LinuxCNC from the loop, replacing it with a 1/2V PSU and switch,  and first tuning the driver, and only add the LinuxCNC position loop and tune that using Tommy's excellent servo tuning guide.
I find the instructions in the drive manual difficult to understand or follow.So if anyone has already set up a JMC servo with analog (Speed control) input, I would love to hear and suggestions you have.
Mark

Hi. always managed to get acceptable results without fiddling with the drive velocity loop. You should be able to get it fairly close by only tuning the linuxcnc pos loop.

Keep in mind that i havnt used JMC servos yet, but i have used a number of chinese brands.

But if you do want to exclude the linixcnc loop, i would do it like this....

In your hal file, connect the position cmd to the position feedback so lcnc thinks it os always in position and ignores the encoder feedback.

Then in your PID loop, make p=0 and give a value to ff1. You will still be able to see the encoder velocity and position in halshow and halscope

Now you will be able to jog with the full load but with no feedback for the position loop.

If you look at halshow encoder velocity while jogging, you can tune ff1 untill the reported velocity from the encoder matches the lcnc jogging speed. That should be what the final ff1 value should be.

Wrong direction.....change the encoder scale sign and/or the output scale sign. It womt run away because there is no feedback and no p.

To tune the drive, now set the acceleration in the ini file to near infinity....99999999 will do. If you now jog, it will seem like a step chamge signal to the drive and you can tune it by looking at the encoder velocity in halscope.

I think that the position feedback or velocity feedback might be reversed. There is an initial small movement in the correct direction, and then it looks like the controller winds up and makes a larger move in the wrong direction.
Can you view the drive's opinion of the movement direction on the display somehow?

it could be that the 0-10 v needs to be reversed if that's the case, the pulse train timing coming in 180* out of sync will certainly cause motion faults. I have the t shirt for that one. IIRC you can change the encoder direction in the configuration utility pnconf

Since you inspired me to start my own Linux CNC mill project i feel obligated offer you some help if you want to. While i have no specific Linux CNC experience i do have quite allot of motion control tuning experience on several industrial motion platforms including designing complete drive concepts from start to finish. Next to that i have a master degree in systems & control theory. If you want we can schedule a Skype call and maybe i can help you understand the manual and explain you the basics of the analog tuning concepts. The only thing that i want in return is that you tell me what info is new to you and possibly this forum then I will write it down so that everybody can use this.

Thanks guys. I tried reversing the encoder but didn't include it in the video, as it gave similar behaviour in both directions.

Henk, thanks for the settings needed to bypass the LCNC loop. That is great idea.

Wout, thanks a lot for your generous offer off your time. I will try to set things up with Henks instructions, and come back to you to set up a call thanks.
Mark