PID tuning the THC

Is there anyone who took the time to PID tune the THC, or does everyone just leave it at the default settings? I ask because I was talking with Cody about how his THC is slow and lags behind, and at times in the past I've noticed that it seems like mine doesn't keep up as well. Despite the fact that my Z axis is capable of 400+ Dinosaurs per minute. He was asking how to speed it up, and since I wasn't completely sure, he resolved to messing with the P value (upwards of 50) to get it to follow appropriately.

At any rate, I am not sure if that is the correct approach or, maybe it's best to ask what the recommended approach is? I know in my research for PID tuning a spindle, it gets complicated, and one recommendation was to set the P value as high as possible until it oscillates, drop it down. and then adding in I and D to fine tune it. Seems much more difficult for the THC.

I have mine at 10 and seems ok for what I do. It does seem to vary a bit between machine, acceleration and velocity would play a part. I think that just adjusting the P would in most cases be sufficient, depending on how particular you are.

If the chief test pilot and keeper of the dinosaurs wishes to play with PID tuning, I would recommend that he installs SIM_PIN in his ini file
linuxcnc.org/docs/2.8/html/man/man1/sim_pin.1.html

And configure it so he can modify the THC PID parameters while cutting. That way you don't have to waste time editing settings between runs.Then you need to spend some quality monitoring arc voltage in halscope. I'm not sure if Plasmac has one but it is also good to measure the error (difference between desired volts and actual volts at a higher scale). Also plot the thc enable signal so you know when pid control starts. There are a number of articles on the net that talk about PID tuning. The Wiki has some good diagrams
en.wikipedia.org/wiki/PID_controller .

I've only ever used the plasmac defaults but have earnt my credentials in THC pid tuning pre-plasmac...

rodw wrote: If the chief test pilot and keeper of the dinosaurs wishes to play with PID tuning, I would recommend that he installs SIM_PIN in his ini file
linuxcnc.org/docs/2.8/html/man/man1/sim_pin.1.html

There's so many things to know about LinuxCNC. It must take years to get your head fully wrapped around everything. And then on top of that, remember all the things you learned in the years previous :laugh:. Well, I guess I learned two things today (Phill implied you can link and unlink pins in Halshow).

And configure it so he can modify the THC PID parameters while cutting. That way you don't have to waste time editing settings between runs.Then you need to spend some quality monitoring arc voltage in halscope. I'm not sure if Plasmac has one but it is also good to measure the error (difference between desired volts and actual volts at a higher scale). Also plot the thc enable signal so you know when pid control starts. There are a number of articles on the net that talk about PID tuning. The Wiki has some good diagrams
en.wikipedia.org/wiki/PID_controller .

In addition, maybe he can move the ball further down the field on his project to add PID control to his Tormach spindle. I got left hanging a bit over in the Pathpilot thread. In fairness, maybe I was asking too many questions at once.

rodw wrote: If the chief test pilot and keeper of the dinosaurs wishes to play with PID tuning, I would recommend that he installs SIM_PIN in his ini file
linuxcnc.org/docs/2.8/html/man/man1/sim_pin.1.html

lol, WTF is that? You keep dragging this stuff up I never heard of. Did you write the docs? lol

SIM_PIN.... lol

bevins wrote:

rodw wrote: If the chief test pilot and keeper of the dinosaurs wishes to play with PID tuning, I would recommend that he installs SIM_PIN in his ini file
linuxcnc.org/docs/2.8/html/man/man1/sim_pin.1.html

lol, WTF is that? You keep dragging this stuff up I never heard of. Did you write the docs? lol

SIM_PIN.... lol

I'm always under the impression that I'm super out of the loop/behind the curve with this stuff. Good to know I'm not alone anyways lol.

bevins wrote:

rodw wrote: If the chief test pilot and keeper of the dinosaurs wishes to play with PID tuning, I would recommend that he installs SIM_PIN in his ini file
linuxcnc.org/docs/2.8/html/man/man1/sim_pin.1.html

lol, WTF is that? You keep dragging this stuff up I never heard of. Did you write the docs? lol

SIM_PIN.... lol

Dewey Garrett made me do it! The original External offset branch he wrote had some SIM_PIN windows that we used to tune the THC PID. It was pretty handy. LIke you I had never heard of it either. I think Bevins the chief router pilot might be able to use it to tune his servos perhaps.