Spindle speed scaling

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08 Mar 2019 08:33 #128066 by thadwald
I am using a Gs2 VFD to run an 18000 rpm spindle. The drive only lets me enter a maximum rpm of 9999, both in the drive setup and in the Linuxcnc driver setup over a serial connection. Using a lower rpm /hz number “works” but the speed is off. Is there a way to scale the speed?

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08 Mar 2019 11:13 #128070 by pl7i92
Replied by pl7i92 on topic Spindle speed scaling
is it a 100 400 or 800hz vfd you got
there are multiple
and see if the settings is 0-10V or 0-5V as it can also be a case

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08 Mar 2019 13:00 #128077 by thadwald
Replied by thadwald on topic Spindle speed scaling
It’s a 400 hz vfd and the spindle calls for 300hz@18000 rpm. I am connecting over Modbus via the gs2 driver and an rs232 connection.

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10 Mar 2019 23:39 - 10 Mar 2019 23:39 #128278 by thadwald
Replied by thadwald on topic Spindle speed scaling
I was able to scale the speed by scaling the spindle.0.speed-out and connecting the scaled speed to the vfd speed.

I have an issue now with the at-speed pin on the gs2-vfd component. It doesn’t ever turn on. I figured that maybe I’m breaking something by scaling the speed but I also tried it without scaling the speed and it still won’t turn on. Has anyone gotten it to work?
Last edit: 10 Mar 2019 23:39 by thadwald.

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11 Mar 2019 12:55 #128320 by andypugh
Replied by andypugh on topic Spindle speed scaling
I wonder if at_speed actually works?

The code is here:
github.com/LinuxCNC/linuxcnc/blob/master...comps/gs2_vfd.c#L392

I would have expected a bit of "fuzz" on that comparison.

Do you see the freq-cmd and freq-output HAL pins becoming exactly equal?

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13 Mar 2019 00:45 - 13 Mar 2019 00:46 #128476 by thadwald
Replied by thadwald on topic Spindle speed scaling
It works. Kind of. I think I have a different problem.

At-speed sometimes turns on immediately, sometimes after several seconds, and sometimes not at all.

Sometimes the vfd stops responding altogether and I need to cut the power to make it stop if it’s running. In order to get the communication up again, I need to unplug the usb-rs232 converter and restart Linuxcnc. I’ve tried two different usb-rs232 converters and they both behave the same.

I’m thinking its either an EMI or a ground loop issue. Or maybe something is wrong with the VFD.
Last edit: 13 Mar 2019 00:46 by thadwald.

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13 Mar 2019 00:55 #128477 by tommylight
Replied by tommylight on topic Spindle speed scaling
You can try lowering the communication speed of the RS232, but it is much more advisable to check the grounding and shielding.

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13 Mar 2019 03:07 #128480 by thadwald
Replied by thadwald on topic Spindle speed scaling

You can try lowering the communication speed of the RS232, but it is much more advisable to check the grounding and shielding.


Yeah. I assumed that the negative pin on my usb-rs232 converter was grounded and used that to ground the shield on my cable.

It’s not:


And grounded:


The noise all seems to be coming from the vfd.
Attachments:

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13 Mar 2019 04:24 #128485 by thadwald
Replied by thadwald on topic Spindle speed scaling

I wonder if at_speed actually works?

The code is here:
github.com/LinuxCNC/linuxcnc/blob/master...comps/gs2_vfd.c#L392

I would have expected a bit of "fuzz" on that comparison.

Do you see the freq-cmd and freq-output HAL pins becoming exactly equal?


If you would, could you direct me to how I would modify the maximum RPM to something that works for me, instead of using the scaling hack. I could just change that number before I compile it as I am currently running 2.8 compiled from source. How would I then handle future upgrades without breaking my build?

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13 Mar 2019 11:06 #128500 by andypugh
Replied by andypugh on topic Spindle speed scaling
I took apart a cheap USB to Modbus dongle, swapped the USB plug for a pin header so that it would fit directly to a motherboard USB header and also changed the 2-pin screw terminal block to a 3-pin with a connection to the USB ground. (not 0V)

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