i've got a weird problem

[fast89]

I converted a Bridgeport j-head to cnc using servos and g320's, and a Kelling power supply. I originally started with stepper motors but had some issues loosing steps and decided to change to servos. Well my servo on the x axis will randomly move it's position. With no movemnet comanded and the motor sitting idle, it will randomly move .002-.010". i've even seen it jump .030" Last night i left the servos powered and the pc off to eliminate the pc, well i checked it this morning and x moved .084". This is not dithering or hunting, it just moves as if it was comanded. this can occur while running a program too which really creates problems. I even installed a 4' ground rod thru the concrete 2' away from the machine thinking that it was noise. tonight i disconected the step and direction wires from the drive to eliminate the break out board. I guess the next step is to eliminate the servo and encoder. Any one ever hear of this or have some suggestions?

[fast89]

Well last night i left the servos powered with the step, direction, common disconnected from the drive. It kept position, woohooo. Looks like my problem is in the parallel cable or the breakout board. Guess i'll try switching pins on the b/o board and see if it's just on the terminals i was using in he cable and board.

[rippersoft]

Are the cables shielded? Are they running anywhere near a source of electrical interference?

RipperSoftware

[Khalid]

Check if there is any ghost there....i doubt this is spiritual problem rather technical

[fast89]

My first thoguht was noise in the cables but they are shielded and seperated. I did perform an exorcism but no ghosts left. I changed to 500cpr encoders and moved the x axis from pin 2&3 to pin 8&9 on the breakout board and my problem is gone. It was pin 2&3 that was causing my problems. Whether it's the cable or breakout board, i don't care, i can run the balls off of it now and get some chips made.

[fast89]

As usual, i spoke too soon. The x axis servo is still jumping. I'm going to leave the parallel cable disconnected from the break out board tonight and see if it still does it. Maybe it's in the g320 but only if step/direction wires are connected?????

[SORCHEROR]

you can switch one gecko with the x and also switch one encoder,its alot of work but someitmes needed to debug these ghost problems,one question before you do,are your motor cables seperate from the TTL cables,they need to be,cant be in the same cable even if sheilded,they will interfear,should have two seperate cables for encoders and motor power,same goes inside the controller,need at 1/4 inch or more away from each other,also i had a problem with geckos when they were to close to my power supply

[fast89]

Well after trying many things, i believe i've figured it out. My geckos are mounted on a heat sink located vertically in an enclosure. It didn't dawn on me that the main power switch is located about an inch away from the heatsink and the x axis drive was the closest. I moved all the drives down and it held position most of the day (within .003"). Needless to say i moved the whole heatsink so i've got 2" in between the switch. This is the first time i was able to load the machine and walk away and not worry about sending a 5" drill through the side of my vise. I ran over 100 parts on saturday, the spindle only stopped long enough for me to load it and hit cycle start. So the moral of the story is KEEP ALOT OF SPACE BETWEEN COMPONETS AND DRIVES.

[vtxstar]

So....you think the proximity of the power switch was putting EMI (electro magnetic interference) into the x-drive? I think moving things corrected a loose wiring issue but, if it's working...don't mess with it!

[rdpzycho]

torroids can help in cable noise problems. even if cables are shielded, common mode noise still pose a problem. it seems like there may be some hidden noise sources or loose connections. studying EMC is too hard.