Messages

41

FAQs / Re: Losing steps or something?

« on: October 26, 2010, 04:37:35 AM »

Hi, again Roger.  Yeah, its hard to do remote diagnostics.  Now to your questions.
1)  4 + wires to Gecko positive terminals.
2) 12 wires...  4 to negative on Geckos, 4 to signal wire shields - at Gecko end only, 4 to stepper wire shields - at gecko end only.
3)  The breakout board is a PMDX 120.  Older model, now considered "legacy". It has its own mains power supply, the transformer in the lower left of the board.  It is driven directly from the Computer.
I removed the temporary earth strap, but there is still continuity from the Cap to chassis.  I don't know where. 
According to the manual the breakout board AND the Geckos both use optical isolation. 
It is on the floor, but accessible.  Looks nice but don't work so well...  I'm wondering if one of the components - BOB, Transformer, ?, could be shorting to ground...  I'll have to try checking.

Don

42

FAQs / Re: Losing steps or something?

« on: October 25, 2010, 02:28:40 AM »

I put a small jumper from the negative terminal to the chassis Aluminum plate, and it had no effect...  Hmmm.  What am I missing, here?
Don

43

FAQs / Re: Losing steps or something?

« on: October 24, 2010, 07:56:22 PM »

Hi, Roger,  Thanks for the suggestions.  I too have reservations about the additional grounding of the motor case for the same reasons you list.  I'm trying to keep every thing single connected so there wont be paralleled circuits.  The motors are indeed bolted to the aluminum mounting plates on the aluminum brackets on the machine elements and have electrical continuity to the chassis.  I don't know how running an additional ground would help unless they were electrically isolated, which would be difficult to achieve.  The capacitor has #10- 32 threaded posts so I was able to get a longer screw to lock everything down.  I haven't gotten to work on the project this weekend yet but I'm going to try to ground the chassis first.  I'll see if that changes the running behavior.  Thanks
Don

44

FAQs / Re: Losing steps or something?

« on: October 23, 2010, 04:59:25 AM »

rcaffin,  all the shielded cables, including the signals are only grounded at the star connection on the power supply capacitor.  I haven't grounded the chassis yet.  I'll try that tommorow evening and see what it does before I try to implement the Gecko suggestion.   Don

45

FAQs / Re: Losing steps or something?

« on: October 23, 2010, 04:55:20 AM »

I could try it...  I've come across a page on Gecko's website on dealing with RFI issues.  It suggests using a 5 conductor cable with the shield.  My step and direction cables are shielded and the shields are attached to the star ground on the power supply.  Gecko suggests grounding the motor case with the 5th wire to the power supply ground and connecting the shield to the electrical box only at that end.  I'll try that as soon as I can.  I'll try using some coax with the shields of the 4 conductor and coax tied together.  
Sorry about the rats nest appearance, there are a LOT of ground connections...  Thanks, Don

46

FAQs / Re: Losing steps or something?

« on: October 22, 2010, 03:09:38 PM »

This is the current configuration of the system.

47

FAQs / Re: Losing steps or something?

« on: October 22, 2010, 03:07:31 PM »

Hi, again...  I've rearranged things and put a new computer into the system but I'm still having trouble.  The new cable to the motors is 4 conductor plus shield and the shields are star grounded to the Geckdrive power supply minus terminal.  I'm still getting offsetting issues.  I'll post some pics of the current setup.  Please tell me if there is anything obvious...
Don

48

FAQs / Re: Losing steps or something?

« on: October 06, 2010, 04:08:43 AM »

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

49

FAQs / Re: Losing steps or something?

« on: October 05, 2010, 04:11:18 AM »

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

50

FAQs / Re: Losing steps or something?

« on: October 04, 2010, 04:46:38 PM »

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