Hey @donkjr , thanks for your reply. Unfortunately my internetz went down this afternoon and Itās only just come back online. The shops will now be closed so trying to deal with my noise issues (if thatās what they are) will have to wait 'til tomorrow.
I have tested the converter, as you suspected, I did mention that in an earlier post. Iām fairly confident the pwm from the smoothie is working properly. To calibrate the converter I used an M3 S12000 command from pronterface which, given my settings for motor speed in smoothieās config, should be giving me a 50% pwm. Sensibly, with a multi-meter on the converter output at this pwm % I get ~5.4v out from the converter. similarly at M3 S24000, the top speed of my motor, I get ~10v. All working as expected. Maybe what weāre not seeing, due to the meter not being able to keep up, is that the voltage is actually fluctuating very rapidly but on the display we just see the expected 5 or 10 volts. To the more sensitive voltage detection circuitry on the VFD this manifests as the oscillations in frequency Iām seeing.
You are also correct about my lack of scope. Pricey! Iāll put one on my to buy list once Iāve recovered from buying expensive lathes, routers and associated paraphernalia.
I also did a test with the pot I found taking 10v from the inverter and feeding it back through the pot to VI1 on the inverter, the set voltage via the pot produced stable frequency, so I donāt think the trouble is at the inverter end in the interpretation of the analog signal.
Iām also not 100% convinced itās noise. Since I donāt have my spindle connected during the tests plus the cabling is shielded, it cant be rf from the spindle cable running near the wires from the converter causing issue. I canāt imagine what else would be generating noise, any clues?
Humour me here because this theory is based on a very limited understanding of electirckery. What I suspect the problem is, is the logic signal from the smoothie not being high enough:
As you state the pwm voltage triggers the optocoupler by switching an led on and off rapidly it must reach given brightness to be sensed as a pulse by the converter. the circuit is designed for 5v input, like you say 3.3v is probably just enough to illuminate the led but even a minor fluctuation in the voltage received from the smoothie might cause the brightness to occasionally drop below the required threshold to trigger the optocoupler, these ālost pulsesā essentially result in a dip in the frequency on the output resulting in the observed frequency oscillations.
I think this theory is backed up by my experimentation with the pwm period. by shortening the period and thus increasing the frequency, the train of pulses received by the converter is a much higher āresolutionā so the dropped pulses have less impact on the frequency output.
So, my idea for the fix thanks to your wonderful pendoodles is as follows:
-
I set up the DAC for 12-24v with the jumper
-
I provide 24v to the DIN+ on the DAC from my 24V psu and connect DIN- to the pwm capable mosfet on the smoothieboard.
-
Set the PWM capable mosfet to open drain in the config with a lower case o.
-
set the PWM capable mosfet as the frequency source for spindle speed control in the spindle module config.
-
Conduct a test with the vfd to see if it works, being sure to cross fingers that the magic smoke stays inside everything.
-
Rejoice at the success of the test and finding the solution to my unstable frequency problems.
My theory with all this in case you hadnāt already guessed is, even with slight voltage fluctuations at 24v, the voltage will never dip below what is required to trigger the optocoupler on the DAC, resulting in a more stable analog output. Seems logical enough, right?
Just need to confirm that Iāve interpreted your diagram correctly and this is a legit way of wiring things, does that seem right to you?
Just to make this message even longer because Iām sure you love reading all my waffle! 
I just checked out your video of the ox cutting out your tape holders, cool invention! Gotta keep that tape organised! Iāve also built an openbuilds design, the workbee which is a variation on the ox designed by Ryan Lock who runs a 3D printing firm here in the UK called Oozenest. I wanted leadscrews on all axes and this design had it. Canāt wait to get cutting. Iām also just getting my head around Fusion too. Like you say, steep learning curve but once it starts to click itās so powerful and quick to reiterate designs and refine things. Iām loving it! If youāre interested thereās some good tutorials at Udemy for fusion made by autodesk themselves and theyāre free, check them out if you didnāt already find them.
Right, Iāll shut up now but let me know what you think of the plan and if itās all safe for my hardware.
Cheers,
Steve
it looks slightly more comprehensive than the garbage I received with mine. Iāll see if I can find a .pdf of the manual for my drive if youāve got the heart to look at it. Iāve read the manual from cover to cover several times but I canāt find any info in there to help with this problem. On the plus side of thereās ever a job going for a Chinglish translator Iāll be a shoe in!
