Setting up Servos in step/dir position mode

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06 Jun 2021 23:20 #211387 by PCW
The reasoning is that it is impossible to generate a 100 KHz step rate (as required by the 50 mm/sec motion and 2000 steps/mm scaling in your .ini file (50mm/sec*2000 steps/mm = 100K steps per second) with the given step timings.

That is, the maximum possible step rate (without violating the step timing) is 1/(steptime+stepspace) which = about 99 KHz with your 5050 ns steptime and step space settings. If you drive can use shorter timings set these (5050) values lower
and higher step rates will be possible.
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09 Jun 2021 11:19 #211613 by RoberCNC
Maybe it is a stupid question but when I am driving servos I should not use INPUT_SCALE and ENCODER_SCALE instead of SCALE and STEP_SCALE forgetting about STEPGEN_MAXVEL / MAXACCEL or this is because being the step & dir signal for .INI purposes it is do they treat like steppers?

Thx.

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09 Jun 2021 14:05 #211620 by tommylight
They are steppers from LinuxCNC point of view.
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09 Jun 2021 14:28 #211622 by RoberCNC
Understood, they will be treated as steppers as long as the command signal is step/dir and it comes determined by the type of controller card.

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09 Jun 2021 17:00 #211628 by PCW

RoberCNC wrote: Understood, they will be treated as steppers as long as the command signal is step/dir and it comes determined by the type of controller card.


Its not really the command signal that's important, it s whether or not LinuxCNC gets
external position feedback from an encoder.
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09 Jun 2021 18:36 #211632 by RoberCNC
Ok, then to treat as pure servos you must connect encoders feedback, but then, as you said before, problems come unless you have scales to fully close the loop.

I will first get acquainted with them in step/dir mode which is how little I know so far and then I will touch on the subject of backlash (pending subject) before going to the next level.

I really appreciate the help and info mates.
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10 Jun 2021 17:13 #211717 by RoberCNC
Hello again, let's see if you can help me (sure), I'm doing tests and running the machine and it happens to me several times that suddenly one of the servos goes into an alarm state, with the consequent annoyance, I can't give with the reason and I can think of how to identify the problem.
The fault is in one of the Y's (it is dual) and the work is a rectangular matrix of circles. I identify the fault because suddenly he observed that instead of circles there are ovals. What could it be due to?
How can I solve it?

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10 Jun 2021 18:25 #211721 by PCW
I would disconnect the servos from the machine and see if you still get a servo fault
just to eliminate mechanical problems
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11 Jun 2021 10:05 #211785 by RoberCNC
If it seems that the problem comes from the mechanics. I have realized that it would be very useful and interesting to take the Alm signal that the drivers have to connect each one to an input of the 7i76 and in case it happens for any reason to know which driver has failed and all the machining stops, at least the pieces won't be ruined, I hope. Looking at HAL I have found the pin joint.x.error, which I am not sure at all is if I am right and it would indeed be that pin where to link the alarm signal or how to do it exactly.

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11 Jun 2021 10:32 #211792 by tommylight
2.8 and 2.9/master have a pin just for that,
Amp.0.fault
Not sure about the name, i am on the phone, but i have them in use and it works properly stopping the machine and displaying the error about the exact drive that faulted.
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