Help with the big picture

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29 Sep 2023 14:01 #281858 by sliptonic
I have a bridgeport clone (YCM-30) that I converted to LinuxCNC quite a few years ago.  At that time I kept the servodynamics amps and DC motors.  I was driving theme with a Mesa 5i25/7i77 combo.   Manually tuning the PID loops was a pain but I managed it and it has worked well for a long time.  The motors and amps are seriously aging and becoming less reliable.  Lots of errors in the last few months convinced me to pull the trigger and replace everything with new DMM hardware.

Physically changing out the motors was almost trivial.  I'll have to move one bracket that holds a limit switch but I have a plan.  The amps are mounted and powered now.  I still have some wiring but I'm turning my attention to configuration and here's where I'm confused.

There are a lot of options to configure how the Dyn4 drivers talk to the motors.  I'm having a hard time understanding the advantages and disadvantages of those options.  I don't mean specific settings, I mean big picture options like position/speed/torque mode.

The Dyn4 has an autotuning mode.  Does this mean I don't have to do any PID tuning between lcnc and drive?  What settings should I have in my config with this arrangement?   If someone has already done a similar conversion and can point me to a relevant thread I would be most appreciative.

Thanks. 

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29 Sep 2023 15:01 #281862 by andypugh
Replied by andypugh on topic Help with the big picture
If you are using the 7i77 then you pretty much have to use analogie voltage control.
Position control with analogue voltage is a terrible idea, so not that.

Torque control and Speed control can both work, but speed control is likely to be much easier to tune.

I was recently introduced to a very simple and effective way to control an axis under speed control.

Set up the PID for position control, in the usual way.
Connect pid.N.command-deriv to joint.N.vel-cmd

Set P I and D to zero, and adjust the pid.N.FF1 value until the axis speed and commanded speed match exactly.

Then you should find that all you need is a very small amount of P gain to bring things under control.
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29 Sep 2023 21:35 #281885 by PCW
Replied by PCW on topic Help with the big picture
If you are using DYN4 drives, it's probably best to run them in step/dir position mode.

This is because the simulated encoder feedback from the DYN4 drives is delayed
significantly from the analog command making them very difficult to tune properly.

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01 Oct 2023 18:02 #282010 by sliptonic
Replied by sliptonic on topic Help with the big picture
Hmm. Somebody should clue DMM into that. When I purchased the hardware from them they assured me that many people use the DYN4 amps with 5i25/7i77 in analog command/speed control.

Is there a reference configuration for step/dir position mode you can point me to?

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01 Oct 2023 21:38 #282026 by tommylight

Hmm. Somebody should clue DMM into that. When I purchased the hardware from them they assured me that many people use the DYN4 amps with 5i25/7i77 in analog command/speed control.

I am sure they hate me by now, despite offering to help with this issue, several times, i even took the liberty of involving some other members here without prior notification so i can remove myself from this equation, still no word from them. It would have cost them two or three drive/motor sets, that's it.
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By configuration you mean for 5i25/7i77 or DMM?
If for DMM, sorry i can not help.

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01 Oct 2023 21:56 #282030 by PCW
Replied by PCW on topic Help with the big picture
For step/ dir, the default setup and timing should work though you
obviously need a different daughtercard

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07 Jan 2024 18:32 #290129 by sliptonic
Replied by sliptonic on topic Help with the big picture
DMM has been unable to resolve the issue. I don't want to run step/dir. So I've returned the DMM stuff and will be buying something different.

@pcw, What hardware would you recommend for maximum compatibility with my 5i25/7i77 control? I'm willing to throw a bit more money at this to minimize the F*ck-around-factor.

Thanks
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08 Jan 2024 20:24 - 08 Jan 2024 20:25 #290234 by BerTiN
Replied by BerTiN on topic Help with the big picture
PCW post=282030 userid=481
For step/ dir, the default setup and timing should work though you
obviously need a different daughtercard

7i77 can't handle step/dir to drive a servo's driver ?
Last edit: 08 Jan 2024 20:25 by BerTiN.

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08 Jan 2024 20:40 #290236 by tommylight
7i77 can drive velocity mode servos, those are +-10V input drives, also known as analog drives.
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If you already have 5i25/7i77 you can get a 7i85S (there are 7i85 and 7i85S, one is step/dir the other is SSerial, do check that) and can be used to drive any stpper/servo drive in position mode with step/dir signals.
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11 Jan 2024 17:48 #290439 by BerTiN
Replied by BerTiN on topic Help with the big picture

7i77 can drive velocity mode servos, those are +-10V input drives, also known as analog drives.
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If you already have 5i25/7i77 you can get a 7i85S (there are 7i85 and 7i85S, one is step/dir the other is SSerial, do check that) and can be used to drive any stpper/servo drive in position mode with step/dir signals.

Thanks for precisions, Tommylight. While this time, I had a look to these two ways of driving servos.
Finally, most of people use 7i77 for this kind of retrofit, and the step/dir way is not really more attractive than the analog way, specially if you work in a closed-loop way with encoders. Maybe the PID-Tuning could be a little bit touchy.

I'll go the analog way, so. ;)

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