I have tried 0V common and it runs terribly jerky with the breakout board.  Gecko suggested some years ago to use the +5V com. setting as it is supposed to reject noise better.  I'd like to know where the "noise" is coming from.

The noise source can be too MANY earth connections. You need to have one central earth connection and then to make radial connections to everything else. NO cross-links. Me, I would treat this as a separate problem, but I would want to resolve it completely. Using the +5 V as a 'common' only masks the problem.

When I originally was having this problem I was using a move of 1.00 inches.  50 iterations of that took a long time, so I shortened up the distance.  I can see that if this was allowed to go on, a large part run might get ugly real fast.

No reason you couldn't use a move of 0.100" instead. The single-pulse error is not dependent on the length of the move. Try 0.100", 0.101" etc. If your system can handle it, try 0.1000", 0.1005" etc, or even smaller steps.

  Aren't computers supposed to do what they are told?

Yeah, just like children are supposed to ... :-)
Yes, they do (normally) execute their instructions faithfully. But they execute them BUGS AND ALL. If there is a small coding error (or approximation), that will be faithfully executed too.

Cheers

No, Don. I am suggesting you swapping the cables going from the Gecko drives to the motors.

Dan

Ah, I will try that, too.  See the following post for some interesting results prior to getting your most recent suggestion, though.
Thanks, Don

Hi, I've been trying a few things in response to your suggestions and now am confused.

I swapped the X and Y axes at the Geckodrives.  The X axis offsets +.005” the Y axis offsets +.0075 or so...    Seems like it might be somewhere outside the computer now. 

   I checked some voltages...  - side of Gecko power supply cap. to chassis ground measured at 11.1V when idle, and varied around 9.8V when the program was running.  I grounded the cap. to the chassis near the geckos.  The gecko signal common (0V) is reading 0V relative to chassis.  I found no change in behavior after I changed the power supply.
   I changed the axes in the motor outputs and this didn't change the offsetting behavior noted above.  Now It really seems to be something outside the computer. 
   I disconnected the terminal blocks from the X axis gecko -  no power, no signals.  Running the program yields the Y axis still offsetting about +.0075”.  I disconnected the Y axis terminal block and reconnected the X axis and the X axis still offsets +.005”.
   I changed the program to move only the X axis, resulting in no Y axis movement.  The X axis still offset +.005”.  What???  It used to take 2 axes moving  to cause this!  I disconnected the X axis and reconnected the Y axis.  No movement at all.  Whew!  I shouldn't with only X axis moves programmed.
   I hooked up the B.O.B., set to 0Vcommon.  Set motor outputs back correct for the machine.  I ran the diagonal test program:  It runs smooth like +5V common now unlike before grounding the power supply cap.  but...  X axis offset +.005 and Y axis offset about +.0075”.  Running the X axis only program yields X axis offset of +.005”. 
   It seems that now, with the power supply grounded to the chassis, the problem hasn't gone away.  Using the 0V common has only made the problem worse.
   I reset everything back to +5V common, etc. except that the gecko power supply is still grounded.  Results are that the diagonal program behaves as before.  Any axis that starts in the negative direction offsets in the negative direction.
   I ran the X axis only test program.  The X axis now offsets -.005” regardless of whether starting out positive or negative!!!
   I tried changing vectors, ie X-.1Y-.04 etc.  and changing the values does not seem to affect this problem.
      I plan to try to re wire the power supply system in the next few days. 
    A few questions. 
1)When using +5V common for the signals, do I dare connect the common to the Star ground?
2)Should I attempt to connect the computer chassis to this ground?
3)What other considerations should I make?
4)I would appreciate photos of your working systems if you wouldn't mind.

   Thankyou in advance,  Don

1)When using +5V common for the signals, do I dare connect the common to the Star ground?

Dunno - might work, might not, depends entirely on the rest of your config. There would have to be risks to power supplies etc, which don't exist when using a common 0 V.

2)Should I attempt to connect the computer chassis to this ground?

IF and only if you are using a common 0 V for every thing, then this would be a good idea. Here in Australia everything has an earth connection, and safety is much improved as a result.
However, you should ideally have an optical isolation stage in the BoB for safest results. There's a lot of power running around the place, and earth loops can carry surprising currents.

Cheers

Thanks for the suggestions.  My concerns are mostly with regard to frying the outputs of the breakout board.  I'll probably not worry about the signal common as the path is short, but I will try to star ground the shield.  Everything here is supposed to be earth grounded.  My chassis, machine, computer cabinet- they all have electrical grounding through the mains to prevent elecrocution. 

I have one other question.  Would 18 Ga. conductors be adequate for my stepper motors?  I can find 18 Ga. 4 conductor shielded wire but nothing heavier without incurring ridiculous cost.  Besides, I think the leads on the motors are about that gauge.
  Thanks, Don

Hi Don,

18 gauge should be fine. I think it shouldn't have any issues up to some 10 Amps.

Dan

Cable has been ordered.  Should arrive in a week.  I would still like to see pictures of working systems' layouts...  Thanks, Don

Don,

I don't have ready pictures of my machines' cabinets and taking some is a real hassle now. Hopefully someone else could share. If you search the forum though you'd find quite a few. Hood, for instance, posted his photos on several occasions.

Dan

I would still like to see pictures of working systems' layouts...

An open layout where you can get at everything is gold.

Cheers