Centroid Community CNC Support Forum

Hi Marty

I have my shields connected to the d-shell at the DYN4 drive, this is what DMM advises.
I will make sure these d-shells are at common.
I don't think the problem is at the Acorn end, the servos are getting the extra noise steps.
I am planning to isolate the step wiring, putting each axis thru a 75 ohm coax.
I will use the db25 connector at the acorn to do this, I will leave the dir as is, coming off of the screw terms.
I'm lucky, already bald.

Hi All,

Completed relocation of xyz step wires, they now come out of the db25 connector.
The direction and enable wires are still coming from the terminal strips, both in a shielded cable.
All wires are shielded and drains connected on servo db25 shells.
All 6 cables have a ferrite bead on each cable.
Ran program cutting 5/8 deep pocket in .2 steps.
Problem is still there!
Next step? Installing servo drives in separate shielded area.
However for now I am going to take a break from cnc and go to work on my my tow behind MC trailer.
Going to #2 son's home in Buchannon MI. 2260 miles. We will the tour UP Michigan for a week.
I will go back to work on cnc problem in Aug.
You all have a good one.
Bill

Bill, I'm writing this from a smart phone, so forgive me if you answered this. What brand and model VFD are you using?

Marty

Bill,
I read you were using DMM servos/drives. One thing I noticed when I swapped out my Bridgeport to DMM servos was that while the servo motor power leads were shielded, the shield wasn't grounded. I had to cut back the heat shrink to get to the shield to attach it to a ground. If you have noise and no drive faults, it may help.
Dean

Thanks Dean
The 25 and 9 pin connector shells aren't grounded either!
After grounding the problem mostly went away.
Maybe grounding the motor shields will kill problem completely.
I'm going to check the encoder cable shields for grounding also.
Bill

Hi all,
I've been back from vacation for a while now.
Never will do UP again, too many mosquitoes! I only found one NF campground, all other camping was in state parks, $17 to $28 plus $8 per night for
me, out of state. Flat tire on way back in Iowa, great state police officer helped and HD dealer was great too.
Now for the router.
Checked motor cable shields and found them to be grounded, I guess DMM corrected this fault.
Machine is working fine now, but I am confused as to why.
The last change I made included two things.
1. Changed step rate to 200kc. Maybe DYN4 wasn't getting wide enough pulse to trigger?
2. Changed step polarity back to normal.
This makes no sense to me, the DYN4 is looking for a positive step pulse.
The Acorn, when in normal polarity, pulls the step signal to ground. That's a negative pulse.
I am using the machine, it is obeying my every command. If I get curious I will change one of those two things at a time
to see which is the problem.

bilorn wrote: ↑Sat Jun 16, 2018 1:05 pm
1. There is a lot of 60 hz hash on the step pins at Acorn when pins are not inverted.
When inverted the 60 hz hash is gone. When in the inverted position the drift is much less but still there.

60Hz does not typically jump to another cable from poor shielding.
It is more likely that there is a bad connection somewhere allowing a signal to float.
Is the 5V pull up supply grounded directly to the ACORN and DMM COM, not through a ferrite or to chassis, etc.?

The best bet is to fix the noise before continuing. The inverted polarity is just covering up the problem because the signal is pulled low most of the time.