My machine lost it's positioning last night on the last part.  Everything was working smoothly the entire day.  The only thing I can think of was that I was vacuuming near the machine and at one point I got a static electric shock off the vacuum.  My back was turned to the machine so I can't say for sure if the timing was coincident.

The vacuum is on a separate circuit.

Any thoughts or suggestions?  UPS?  How do you determine the size of UPS?

Just because the vacuum cleaner is on a different circuit dosen't mean you can't  pick up noise.
That brushed electric motor in the vac can throw a heck of lot RF /noise out. Not to say that's what caused it
but very probable.
How warm or hot were your motors at the end of the day?
RICH

Hi Rich,

I've been away.  Thanks for responding.  The motors run pretty cool.