Messages

1651

General Mach Discussion / Re: Progressive Move Error with X and Y

« on: August 28, 2008, 10:03:59 AM »

Sage,
    That could be a bad recommendation, depending on which version of the CNC4PC BOB he has.  The earlier ones used *very* slow optos on some outputs (30-60 uSec rise times), so cannot be used for step signals at any reasonable step rate.  The board is marked as to which ouputs are appropriate for faster signals, like step, and which are not.  If he has the current rev of the board, this is not a problem, but with an old one, it definitely is.
    Also, your conclusion in the first paragraph that "the BOB hardware is fine" is a bit hasty,IMHO.  I was able to perform similar tests on my machine, and ruled out the BOB as a result.  In the end, the problems WERE caused by the BOB, which acted up mostly only when multiple axes were running.  It was a number of noise problems and design issues on the BOB itself.  Replacing the BOB has completely cured the problems.

Regards,
Ray L.

1652

General Mach Discussion / Re: Progressive Move Error with X and Y

« on: August 27, 2008, 10:01:57 PM »

Carl,
   I don't know if anyone has brought this up yet, but how is your system grounded?  Early on, my system was losing steps, in part, because of poor grounding.  It's important that you have a very solid, single-point ground for everything.  This one point should be the ground for the line cord, the motor power supply, and the +5V and +12V power supplies for the CNC4PC board.   You should have a single lug securely tied to the electronics case with individual wires running to the various devices from that one point.  NEVER daisy-chain grounds from device to device.   DO NOT ground the PC to the electronics case.  The only connections to the PC should be the parallel cable signal pins, and the USB cable that provides power for the PC-side opto-isolators.  The PC ground should not be connected to the electronics box ground.
   Also, you should be using shielded cables for any limit switches, e-stops, etc., and those cables should have their shields connected to that solid ground ONLY at the electronics box end, NOT at the switches, etc.  Shielded cables for the steppers also would not hurt, as long as you connect the shields as above.
   What rev of the CNC4PC board do you have?  If it's an early one, you really should get an updated one, as there have been a LOT of design improvements made.  My rev 2.0 board was very unreliable in my system.  It drove me crazy for weeks!  The rev 7.0 board I now have has been bullet-proof.
   If you want to bypass the CNC4PC board entirely, wire the PC parallel port connections directly to the Geckos (they're internally opto-isolated), and wire the +5V from the USB cable to the "common" terminal of the Geckos.  That's all you need.

Regards,
Ray L.

1653

General Mach Discussion / Re: layers

« on: August 25, 2008, 09:31:55 AM »

Mike,
    The order in which the layers are machined is entirely determined by the order in which you create the processes in SheetCAM.  Mach3 does not do any re-ordering, it smiply does what the G-code tells it to do.

Regards,
Ray L.

1654

General Mach Discussion / Re: Homing Probem

« on: August 25, 2008, 12:21:13 AM »

I did set 2000 for debounce, but only had to home the machine once today, so I can't say it made a difference.  I'll post the XML tomorrow. 
The important thing to remember is - Once it's in this state, *nothing* I do gets it going again, except re-starting Mach3.  It can't be switch bouncing, because nothing is moving, and, again, re-starting Mach3 gets it working perfectly again, without touching the hardware in any way.  Also, this morning, I turned on the computer, loaded Mach3, and it came up with a "Driver Watchdog Timeout" on startup.  I exited, re-started, and it did it again.  What can cause a driver watchdog timeout?

Regards,
Ray L.

1655

General Mach Discussion / Re: Homing Probem

« on: August 24, 2008, 09:34:44 PM »

Hood,

    The other forum is the Yahoo Mach1MAch2CNC forum.   The thread is named "Homing Problem"

    http://groups.yahoo.com/group/mach1mach2cnc/message/97299

1656

General Mach Discussion / Re: Stepper Motor Loosing steps - I think

« on: August 24, 2008, 05:12:37 PM »

I would try swapping the motors between the two drivers.  I think you'll find the problem follows the driver, not the motor.  Then try swapping the connections from the PC to the drivers.  My guess is you'll find the problem follows the PC connections.  What are you using as an interface (breakout board?  If so, which one?) between the PC and the drivers?

Regards,
Ray L.

1657

General Mach Discussion / Re: Mouse, keyboard disappear then total shutdown, Mach3, Dell Laptop

« on: August 24, 2008, 10:17:39 AM »

"Set Computer to Standard PC NOT ACPI PC" - How do you do that?

Regards,
Ray L.

1658

General Mach Discussion / Re: Homing Probem

« on: August 24, 2008, 10:13:31 AM »

On the "settings" page make sure "auto limit overide" is flagged. This allows you to "back off" a limit switch.

Is the problem always with the same switch. If it is, the switch is probably "noisy" and giving multiple on/off signals as it opens - hence checking the "debounce" as Brett says. If it is not too much trouble you can replace the switch.

Auto Limit Override is set, but doesn't help when this happens.  The problem always occurs with the same switch, but it's the first axis that homes, and when in this state, it never makes it to the others.  The diagnostic page shows the limit is postiviely asserted.  Re-starting Mach always gets it working again, so I don't believe it's a noise problem.  It's a bug in Mach.  From posts on another forum, I'm not the only one seeing this problem either.  Someone else is having it on both his lathe and mill.

Regards,
Ray L.

1659

General Mach Discussion / Re: Homing Probem

« on: August 23, 2008, 10:46:38 PM »

Brett,

    I'll give that a try tomorrow.  Thanks!

Regards,
Ray L.

1660

General Mach Discussion / Re: Power Supply(s)

« on: August 23, 2008, 07:40:54 PM »

I am pretty sure in a discussion I had with Maurice at Gecko a few years ago he mentioned there was no problem  running dc brush type servos at 50% or so higher voltage than the motor rating, something to do with the way the amplifiers work , I know a couple of machines I have worked on in the past (mold handling equip) have had 90vdc motors working with 170+- vdc power supplies.

I know the old bridgeport I am working with came fitted with Reliant 90vdc motors and the original power supply is 177vdc.
I know very little about dc servos and power supplys beyond the basic wiring , just passing along past exp

That seems like a bad idea to me.  With servos, you *want* to be able to run high current briefly, to deal with load changes and accelerations.  But, Geckos only have a single current limit adjustment, so it will be active all the time.  If you set it to the motors rated current, them you won't be able to get the peak torque to handle transients.  If you set it for a reasonable peak current, then if you stall the motors, you'll likely exceed their voltage rating.  Mariss indicated to me that the proper thing to do is generally to leave the current limit all the way up, and just use a power supply that is at, or only slightly above, the motors rating.

Regards,
Ray L.