PWN CNC Spindle Connection to Acorn Controller

[ALSjosh]

I am seeing some assistance with making the VFD connection to my new Acorn motion controller with the MX6 cable. I am converting my Shapeoko 5 Pro over to a Centroid Acorn controller and the motion controller has some slight connection differences from what I found on the pwnCNC knowledgebase. I will attach a PDF of the Acorn schematic for a “generic VFD” and the screenshot I found on the knowledge base for reference. The VFD type used in the pwnCNC enclosure is a Delixi EM61 FYI.

I am assuming the following connections…

(MX6 Cable to Acorn Controller)
Digital Common -> VFD Common
Forward -> Spin forward
Reverse -> Spin Reverse
PWM -> AN Out
GND -> AN GND
10V -> ???
Shield Drain > Acorn chassis ground

https://support.pwncnc.com/kb/article/1 ... ntrollers/
https://www.centroidcnc.com/dealersuppo ... 983.r3.pdf

[cnckeith]

0-10 vdc analog out on the acorn is not pwm.

Acorn pwm out is on the db25 connector

do you have the manual to the spindle controller? if it accepts 0-10 analog you don't need to use pwm.

[centroid467]

The VFD will accept analog 0-10V DC on terminal VF1. This is selected by P0.0.04 according to the EM60 series manual on the pwnCNC website (here: https://support.pwncnc.com/kb/article/37-vfd-manual/)

If it has the expansion card then it might be set up for some kind of pulse input on DI6 but otherwise I would expect them to have put 0-10v or 0-5v PWM to terminal VF1. How is it wired inside the cabinet?

Anyway, you do not need to connect the 10V line as the Acorn will provide that itself. Your intended wiring looks good to me as long as the wiring inside the cabinet is correct (AN_OUT -> PWM -> VF1) and the VFD parameters are correct.

[ALSjosh]

@cnckeith @centroid467 I have not cracked open their VFD housing just yet to see how it is wired. Is PWM signal better than 0-10v or no? I should mention I also have the Gecko G540 for stepper drive but was looking to control the spindle off of the Acorn to simplify things. Thank you both for your response.

[centroid467]

I think it would be better to use 0-10V analog in this case. No real reason to choose PWM over industry standard 0-10V for spindle control unless the hardware works better with PWM which I do not believe is likely.

It is probably a good idea to crack open that VFD cabinet and check the wiring and VFD settings before trying to control with the Acorn.

Edited: I think the pwnCNC documentation might be conflating PWM signals with analog because you can indeed use PWM to generate an analog signal or maybe they are thinking in terms of the average voltage. Basic PWM will give you a signal varying in average voltage proportional to the duty cycle but the peak voltage is always the full output voltage. If you add a suitable low pass filter to that output then you will have a reasonable analog signal at the average voltage of the PWM signal. The sampling interval of the analog input on the VFD would act as a low pass filter although I would rather have a hardware filter to ensure the signal is clean. This is an easy way to add a lower precision DAC to a project without adding dedicated DAC hardware.

However, there is no reason to use PWM this way if you have a dedicated DAC. The Acorn has dedicated DAC hardware for the purpose of spindle control so it makes sense to use it.

[ALSjosh]

So, I had time to open up the VFD enclosure today and did confirm that the “pwm” wire was terminated in the VF1 terminal. So it sounds like I just need to eliminate the 10v wire and the below should work?

MX6 Cable to Acorn Controller)
Digital Common -> VFD Common
Forward -> Spin forward
Reverse -> Spin Reverse
PWM -> AN Out
GND -> AN GND
Shield Drain > Acorn chassis ground

[centroid467]

Yep, that wiring should work!