Encoder Pins linked to LCNC

tommylight wrote: Adjusting the drives should be avoided, they are supposed to drift slowly when no input is present.
Have to read the rest of the thread as i read everything and i do not want to mess something.
Linuxcnc when properly set and enabled, no drift should occur and if you try to move the motors manually they should resist vigorously.

Tommy: Is this true? I also read JTs post about setting the drives before tuning, and zeroed out all drift. Is this part of the reason I am having trouble tuning my servos?

Also on a tangent...

If anyone has a early 80's Hurco KMB1 and has any questions on how to interface with the machine, don't hesitate to contact me (Just so you know, I am not on here every day... very busy).

I have the complete operators manual, parts manual, and wiring schematics. I have kept all of my OEM parts in the machine and simply removed the computer and power supply, then wired directly into the TB3 and TB8 connectors, plus other wiring that went to the OEM computer. Let me do state that I am not a electrical and/or mechanical engineer and simply would give info and help to anyone that was in my situation (stuck like chuck), and do not assume any liability... in layman's terms I don't want anyone to get hurt or killed... This is suppose to be a positive experience, not a negative one.

Thanks,
Robert

Slow drift on analog servos is normal and not terribly significant _except_ that it indicates a LinuxCNC setup issue:

The drives should not be enabled before LinuxCNC explicitly enables them

This is a machine/personnel safety issue for a couple or reasons:

1. Eventually you may drift into the machine stops and break something

2. LinuxCNC cannot disable the drives in case of a following error, for example from a broken encoder or bad analog signal, so a large class of potential runaways cannot be prevented

The effect of slow drift on tuning is not significant (it will cause a very small fixed position offset) , and can be adjusted with the PIDs bias pin

PCW wrote: The drives should not be enabled before LinuxCNC explicitly enables them

No worries there, I have the drive-enable hooked up. (The only issue I have is when I forget to turn on the air to counter for the Z weight, and the Z drops a little as the brake releases slightly before the drive engages! :pinch: )

My concern is Tommy's comment that "they are supposed to drift slowly when no input is present" (I purposely did this to TUNE OUT the drift) - my servos are rock-solid with AND without input. (Altho' I expect this may vary with temperature?)

I think "may be expected to drift slowly" is closer to the hardware behavior of analog drives ( Ideally they should not drift ), and yes its will often change a bit with temperature, after all a 1 RPM drift of a 2000 RPM servo motor is only 5 mV.

The static error created by a DC offset (assuming no I term and 10V analog scale ) is just the offset/P-Term so if you have a P term of 10 and a offset of 10mV, this would create
a 0.001" static offset

In my initial efforts to tune the servos (not terribly successfully, I might add!), is that if I add any value apart from P=1, my servos do weird things. I've yet to play with FF1, which I understand, is required for velocity drives? Oh, and I also need a little bit of deadband. But nothing else! But they don't drift.

Anyway, I've taken this way off-topic; I'll start a new post when I get to tuning! Thanks PCW.