Spindle speed scaling

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?

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

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.

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?

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.

tommylight wrote:

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.

andypugh wrote:

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?