5i25 with 7i77

I recommend servo tuning in AXIS. Yes the tuning will be overwritten if you use pncconf again. (unless you take note of the changes in the INI from tuning and enter then in pncconf)

Pncconf gets the basics laid down then most people hand edit from there.

Chris M

I sincerely appreciate everyone's help so far. I have two short videos with a quick question pertaining to each. I have my motors and encoders wired up to my 7i77 and am in the process of tuning the servos. Before I get started I noticed a few odd behaviors. Let me preface by saying that I have removed the belts from all the motors, they are not connected to the ballscrews, there is no concern for movement at the moment. That being said, when I enable the servo drives with a jumper, I have the drives zeroed so there is no drift, (I mean there is some degree of drift obviously but it is so minuscule that it is not discernable to the human eye). When I enable the drives through the 7i77 and linuxcnc under the Pncconfig wizard, all three of my axis motors begin to drift clockwise at a rate of about 1rpm as depicted in the first video. All three motors jog back and forth in each direction without any problem and appear to function correctly otherwise. Is this drift in Pncconfig a normal behavior?


My second odd behavioral question pertains to an anomaly that shows up when I try to enable the drives in the axis GUI. As you can see in the video below;

The drives enable for a fraction of a second during which time the X and Y axis begin to drift, at which point the system quickly disables the drives and gives me a joint 0 following error, which I assume is a natural response to the movement in X and Y as a safety measure. As you can see the X moves consistently in the positive direction while the Y moves back and forth between the two. Is this a common behavior for an untuned servo? I am curious if this is indicative of another issue. I am fairly confident I have all my wiring correct. I don't believe I can move forward with servo tuning in axis if I cannot enable the drives so I guess I am stuck at the moment. I have an analog oscilloscope at hand and was able to get Halscope to function when I played with it; is there any further data I should gather. I am going back to the shop this weekend, any suggestions would be sincerely appreciated!

A couple things:

1. Expect analog drives to drift somewhat if the loop is not closed
This should not be an issue since the drives should not be enabled
until linuxCNC is running and the position feedback loop is closed.
(actually getting the drive enables working is the first thing to do)

2. When you first connect the drives and enable feedback, you may have the feedback reversed so the drives runaway (till you get a following error)
You should follow setup/tuning instructions like JTs here:

gnipsel.com/linuxcnc/tuning/servo.html

Excellent! This is the first time I have seen that particular servo tuning tutorial. Something immediately jumps out to me, under Prepare to tune", bulletin point 4, John says "Verify feedback direction (expect runaways) you may have to change the sign of the analog outputs." Can you elaborate on what he means by "change the sign of the analog outputs." The first thing that comes to my mind is the +-10v analog output and the associated 0v com wire. I say this because when I began working on the machine in question (an H.H. Roberts TW-31-MV by the way) I noticed that it looked like the servo drives were wired in reverse. I have attached the drive connections PDF and also a closeup of the drives as they were originally wired. You can clearly see the +-10v red wire and the black 0v com wire are backward according to the connection diagram from the manufacturer. At first, I had just attributed this to a peculiarity with connections on the defunct Anilam controller. Might they have done this intentionally to allow compatibility with an unusual encoder orientation?
I am farmiliar with basic AC/DC circuitry having soldered together electronics kits since I was a child, I am however not familiar with industrial motion control yet, I recently finished with a computer integrated machining program at our community college and have begun working in the industry operating an EDM machine for a local tool and die maker. However, since taking on the project of retrofitting this machine, I have learned am very fascinated with the control behind a CNC machine and have decided to go back to school part time in the Mechatronics program so I can gain a much deeper understanding of everything involved with industrial motion control. Also, because if I want to get anything done at work, knowing how to operate the machines apparently isn't enough, you have to know how to diagnose and repair the damn things if you want to make regular progress with my current employer. But I want to again thank you all because I would not be on my current track without your help!!!

forum.linuxcnc.org/10-advanced-configura...ning-detailed-how-to
All the info on 7i77 servo wiring and testing and tuning.

PCW wrote: A couple things:

1. Expect analog drives to drift somewhat if the loop is not closed
This should not be an issue since the drives should not be enabled
until linuxCNC is running and the position feedback loop is closed.
(actually getting the drive enables working is the first thing to do)

2. When you first connect the drives and enable feedback, you may have the feedback reversed so the drives runaway (till you get a following error)
You should follow setup/tuning instructions like JTs here:

gnipsel.com/linuxcnc/tuning/servo.html

To relate this to pncconf's 'open loop' test - it will drift because there is no PID connected.
The open loop test to to test/conform the feedback and command direction.
When you press the positive button the the feedback should count positively and the axis should move positively.
You can also confirm the scaling is right.

Once you confirm this then you should tune PID in AXIS.

Chris M