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Hi all, I am having trouble controlling spindle speed with my YL620A VFD and AXBB-E board.

I have verified that the VFD will control the spindle speed by the knob on the VFD so I know the VFD is working properly. I can turn the frequency down as low as 50Hz and the spindle still turns.
Using the UCCNC software I can start the spindle with an M3 command but only when speed parameter is 15000 or more. I can reduce the speed via the slider or button but it will not go any slower than 9000 rpm.

PWM frequency is 400Hz
Speed range is 0-24000

I just ran some tests to see the voltage at the VFD.
In the MDI I entered M3 S15000 to start as it will not start at a lower speed even though the speed can be reduced once running.
Speeds and voltages as follows:
M3 S15000 = 5.97V
M3 S13000 = 5.08V
M3 S12000 = 4.69V
M3 s24000 = 9.68V

I also tried starting the VFD via the MDI at 12000 rpm without success but the frequency display showed 223 Hz. That makes me think that some setting in the VFD is not right.

The VFD also need a start signal. It sounds like you only sending the analog Voltage, but not switching the start input on the VFD to make the motor runnig.

Ok that makes sense. Where does the start signal come from on the AXBB?

I think I figured it out.
I need to go from Isolated Output 1 and Output 2 to the fwd and rev on the VFD and a common from -24v

Well as it turns out it was already wired exactly like this so I'm completely stumped as to why it doesn't work properly. Other folks with the same VFD and spindle combo can start their spindle at 8000 rpm no problem.

Did you measure the start signal, is it there?
And did you configure the VFD to accept the start signal from the screw terminal instead of from the front panel buttons? You have to do this too, there is a parameter for it in the VFD, check it's users manual.

I did not measure that. I will though. I do see the indicator for the output is lit on the diagnostic panel.
What should I expect to see?
Yes the VFD is configured correctly to be controlled via the software.

Usually the VFD has a pullup resistor inside to 10Volts or to 24Volts and the AXBB-E output pulls it low to start the VFD, so you should see high voltage (10V or 24V) when the signal is inactive and 0V when the signal is active.
So, you should have 0Volts on the start input terminal and some voltage (higher than 0V) on the analog input for the spindle to start.

Thank you, that's very helpful.