Unusual Movement

I have been converting my existing mill from parport interface to a 5i25. So far I have everything functioning ... except something seems odd about the movement. I can rapid across the table just fine, the deceleration is okay, but in the final few mm's it moves really really slow before coming to a stop. Is there configuration to change this?

LinuxCNC 2.7.4
Mesa 5i25 to existing (parport) Controller
3-axis Mill using Steppers

PS: I wasn't sure which topic to put this under.

Try setting the P term to 1000

( assuming this is a pnnconf configuration )

Excellent thanks. I had just been reading your other post "suboptimal P settings" and thought it might be related.

I have a longer servo thread period, so using your calculation:
P = 1 / (servo_thread)
P = 1 / 0.003
P = 333.33
The movement is working correctly now.

I have a long servo period due to infrequent high jitter. One day I'll get some time to investigate it ...

Initially this seemed to have resolved it, but there is still something not quite right.

(1) Infrequently the final movement (before coming to a stop) moves very slowly.

(2) Jogging (in any axis) with fast speeds is very smooth. However, jogging at slower speeds is not smooth, and randomly sounds like its either missing steps or decelerating/accelerating.

How bad is your jitter?
Can you post your hal/ini files here?

I have found this same type of movement in a new 6i25 installation by pncconf. Pncconf has set P=20 and FF=1 as default.
When I get to this machine next time I will try to change P to 1000, but what about FF?

Setup is Debian Wheezy with LinuxCNC 2.7.4
PnCConf is Beta 1
Mesa 6i25 controlling three Gecko G213V directly.

FF1 must be 1
P should be 1000 for 1 KHz servo thread

I changed P in my machine file to 1000 and this worked out very well.

Then I wanted to run Pncconf to improve on my axis timing.
I could not change the P values in Pncconf, the numeric fields were grayed out. I manually edited xP etc. in the .XML file but I suspect there is a way to change PID parameters in the Pncconf menus.

If you want to change step rate in Pncconf axis test, the axis has to be enabled and I tried similar variations for PID parameters but no luck.

So, how do one change PID params in Pncconf?

Like stepconf, pncconf works well for making an initial ha/ini file set but
later changes are best made by direct editing of the files

If you want to change the PID parameters on a live system, the calibrate menu in Axis is a good way
Note that there is really not much to tune unless you have special problems you need to solve

P=1000
FF1=1
everything else 0

Is very close to optimum for a 1 KHz servo thread system