Mesa 7i97T & LinuxCNC setup struggles

P=5-10 I=0 D=0
FF1 - 0.024 but still tweaking.
Deadband 0.00001

the servo will move but if the P value is much higher it will oscillate more and more untill it trips following error. the F error max limit is set at 50 currently which is ofcourse way to high for normal operations

Are you sure the drives are in velocity mode?

If they are in torque mode, the tuning is completely different.

In velocity mode, the motors should strongly resist any attempt
to rotate the shaft (even with P=0)

i have struggled to find out what "mode" my drivers run in. as far as i can tell there is no option to choose between the torque or velocity. 

My drivers are Advanced Motion Control (branded as Precision Valve & Automation) B12A6F-PV2. i have not been able to track down any manual or documentation for this specific drive, but i do have a general setup guide from AMC which covers this era of hardware and gives me some idea of how to operate it. 

www.a-m-c.com/wp-content/uploads/support...ual_Analog_Panel.pdf

However in re reading the above documentation i think the dip switch labeled "open loop" on my drive (which is switched off) is the mode change switch, with "open loop" being velocity, and the alternative being torque. Pages 14 - 16 have the modes of operation, but my drives do not have all those options. below is an image of what i have showing the pots and the dip switches. 

www.a-m-c.com/product/b12a6/




 

Do the motors have tachometers connected to the drives?
(these are needed for velocity mode)

 

There are three hall sensor wires, which have been pre wired as i got the servos and drives as a set. i dont think this is the same as a tachometer?
There is also a 2000PPR encoder which is wired into the Mesa card

Without Tachometer feedback, the drives are running in torque mode.

There are a couple of options for controlling this:

1. Run as is with different tuning. For single loop torque control tuning is basically:

   A. Increase D term as far as possible until you get buzzing/hf oscillation
   B. Then increase the P term until you get instability and then back off to about 50% of that P value
   C. Increase the I term until you get instability and again back off on the I term about 50%

2. Use a spare analog output channel to simulate a tachometer so the drive itself can run in velocity mode

3. Use a dual PID loop control in LinuxCNC (inner velocity PID loop and outer position PID loop)

im starting to think i might have something else going on.

with your point in the right direction and reading the documentation again, this time having had more exposure to terminology, i can find the modes and how to switch them. ive looked into the above three options and i think for now atleast i will run them as is, in torque mode.

Ive since double checked the servo drive settings and balanced it all so there is no movement when enabled. the drives also have a handy test option which internally feeds a +/-10v signal into the input for testing, this confirms the drive is set well and the motor functions very nicely. in fact the settings I landed on are near enough exactly the same as the remaining two untouched, as delivered, pulled from working machine (which much have been setup to run torque mode.

however when it comes time to have linuxcnc command movements, nothing is really behaving as i would expect, and i cant even begin to work through your above torque mode tuning process, because if i put even a 1 in the D field i get instant following error and a blip on the motor (P & I - 0), FF1 tried several 0 thru 1 ect), deadband 0.0001

ive confirmed its not runaway, because changing the sign on the scale makes that blip noticeable worse, presumably this is runway before the following error cuts it off.

the servo drive is now back in the same configuration it was when i began trying to incorrectly tune with tommys velocity mode guide so all info with reguard to some unstable movements with low P value, is still relevant, nothing useable though. Ive attached hal and ini files incase relevant.

given my struggles have quickly moved on from software installation into the seemingly typical noob hardware problems, if the mods would prefer to move this into a more appropriate channel that's fine by me. 

as always, thanks for everyones help, as a try DIYer, please know how much it hurts to ask for help and how needed that help is, if im asking 

I would try setting the following errors wider so you can see the actual behavior without getting an instant following error
(say 25 and 25 mm)

Then first set the PID up with all terms 0 except a small amount of P

Then check if the motors roughly hold position and move when jogged

 

Yesterday evening i was using chatgpt to help understand some of the nuts and bolts of what certain values mean. i made progress but perhaps you can check its homework.

i did set the following errors wider which has prevented this error occurring for the most part, though i understand this should eventually be taken right back down to the tight window it should be.
FERROR = 10
MIN_FERROR = 5

notably, it suggested changing the PWM scale from 10 to 1, claming that this would provide the expected +-10V and the voltage limits coming from the max outputs which on the surface makes sense and got me to the point where i was tuning a motor that was either violently oscillating or buzzing angrily, tuning pid values to a very low point gave a quieter (but not silent) motor but it was sluggish.

Now it could be that im not in a position to tune properly, or i could have screwed the code up much worse because i am quite aware that chatgpt is not our savior and it will be confidently wrong.

the documentation here supports the claim that the scale should = 1 however im not certain why mesaCT set that scale as = 10

www.linuxcnc.org/docs/html/man/man9/pwmgen.9.html

feels like progress, and i dont think im far off cracking it.

Changing the PWM scale changes the scaling of all PID parameters.
That is, a P term of 10 with a PWM scale of 10 is the same as a P term
of 1 with a PWM scale of 1, In both cases an error of 1 mm generates a
full scale (+ or - 10V)

There is no reason on a torque mode drive to change the default 
PWM scale of 10 (a scale of 10 means the PID output is scale in volts)