spindle speed eratic with delta vfd

[GDawson]

Good Evening, My uncle recently acquired a Laguna IQ router for cheap, its pretty nice, but they cut some corners with the control system and we saw the acorn and an atc spindle as the logical update. currently we are figuring out the spindle drive, we have direction and speed control but the speed is unstable in the bottom half of the range, rock solid at full chooch. We bench tested the acorn, and the voltage outputs look really good (as expected and stable) but when in situ we are getting hunting rpm and a sort of dead spot in the say 2-4v range. any thoughts? shielding? twisted pair? needs a signal isolater? interestingly enough when I monitor the voltage with my fluke 117 the drive behaves better, almost like the high impedance measuring circuit is helping.. (I did verify its not loose wires, and I used quality 18ga wire, plus its real short, only 20") I don't have a scope handy, but I really should get one.
any thoughts or experience is appreciated!
-Greg

[tblough]

You might try a 0.1uF ceramic capacitor across the Acorn's analog out lines.
https://centroidcncforum.com/viewtopic. ... 608#p33606

[GDawson]

Appreciate the input Tom, things are progressing well xyz all moving well, just need a bit of calibration (2 or 3% error) new atc spindle is in and running closed circuit water cooling is also done. will try the cap on the signal lines and see what we get.
-Greg

[eng199]

Another link about analog output filters:
viewtopic.php?p=46032#p46032

[GDawson]

Today's update, found an organizer drawer of 40 year old ceramic caps, the writing on them is basically illegible and they are running just under where my meter reads, so I'm guessing high pico farads, maybe 1-2 nf.. snapped the system right around, frequency fluctuation is now in the .1hz range, not the 10's. not good enough for rigid tapping I'm sure, but this is a router. for reference the cap is just shy the size of a dime Thanks for the suggestion Tom.
-Greg
for reference I placed the cap at the output of the acorn, not the input of the delta vfd

[tblough]

Centroid's rigid tapping works by slaving the Z feedrate to the actual spindle rpm as measured by the encoder, not the other way around. Small speed fluctuations will NOT cause a problem.