Slaving the second gantry motor (7i92)

OK, it appears that I've got "joint mode" and "world mode" confused.

When I select Joint 3 and hit the "+" button, the second gantry motor DOES move, by itself, and has holding torque.

I do expect it WOULD work in World Mode, except any attempt to move any axis gives "Following Error". I did have the speeds set high, although they should be correct. I reset MAX_VELOCITY to 5.0 but no change.

I tinkered with this for awhile, but no change. I don't quite get it. This is a "PID" .ini file which is different than other examples, is something inappropriate about that? (I included my .ini and .hal files earlier in the thread).

Hmm I increased FERROR to 0.005 and got axis 2 to move in World mode, but the other axes still generate Following Error even with the FERROR increased like that.

Then I increased FERROR to 0.2 and both X-steppers DO move in World mode... but only once. As soon as I release the + or - button, both Joint 0 and Joint 3 report "Following Error" and the system stops.

EDIT: Well, what I realized is I could move the gantry with MDI G0 without error at 300ipm. It was only manual jogging that caused the Following error.

300 ipm is abnormally slow. I bumped the max velocity up to 1200 ipm the router is meant to do. Now MDI G0 moves START working- but after a few inches it halts with a Following error. Which suggests to me it's breaking when it exceeds a certain speed and just took a few inches to reach that speed and broke.

I saw this could be an inappropriately long BASE_PERIOD, but that's not even used for 7i92 generators, is it?

It sounds like your stepgen acceleration is lower than your axis accelleration.

Is there any reason you chose to use a PID setup?

I wasn't able to get any automated setup for the 7i92, and someone volunteered this file as a 7i92 config for use with a G540 and steppers. No, really, I don't even understand what purpose a PID has with steppers, but it was literally all I had to go on.

I did try to follow the "stepgen max" rule given.

MAX_VELOCITY = 20
MAX_ACCELERATION = 80
# Set Stepgen max 20% higher than the axis
STEPGEN_MAX_VEL = 24
STEPGEN_MAX_ACC = 96

I've tried other numbers since this.

It may be that the PID is maxing out. What are the PID limits set to?

Running a step/dir drive in velocity mode with a PID can have some significant advantages, but it does mean that you need PID tuning, just like any other pid-controlled system.

I included the .ini and .hal files a bit earlier, I've tinkered a bit but didn't touch the PID parameters, I don't even understand them.

andypugh wrote: It may be that the PID is maxing out. What are the PID limits set to?

Running a step/dir drive in velocity mode with a PID can have some significant advantages, but it does mean that you need PID tuning, just like any other pid-controlled system.

Well, I really really wish I wasn't trying to deal with the extra complexity of a PID. It's super-unfortunate that it's there, but I literally had no other options for figuring out a 7i92 config. I mean, I don't know enough yet to remove it and it's not otherwise working so hard to tell if you're breaking something. Trying to hack it out now would only make the task more complex. Once the system's working fine, well, I wouldn't be so concerned about the PID code being there, even though that would be a better point to try to remove it.