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General Mach Discussion / Please Help!! Dell optiplex mach3 problem

« on: September 29, 2010, 08:06:44 PM »

This one has me stumped. I have been experimenting with Mach3 on my Toshiba laptop with vista64 for about a week. Everything seems to function normally, but it has no parallel port and I didn't want to use smoothstepper. I bought a used Dell optiplex g280 on ebay to dedicate to cnc but it will not finish a run of code. I can look at the code in any editor and it is ok, but mach3 gets to somewhere in the neighborhood of line 150 and stops cold. The window where the code is displayed shows the line it stopped on and all lines after it being identical. If I take the very same file and run it on my laptop it completes without a problem. I first ran Win7 32bit on the Dell and when the problem showed up I loaded a clean XP sp3 32bit. It still does the same thing. Drivertest shows the system as being excellent with less than 2 us variation. The system is a 3ghz processor with 1 gig of ddr2 memory and a 80 gig sata drive. I can't begin to understand why it is so different between two computers with the very same file. files are created with Mastercam and I have tried every post possible and they all do the same, so I have to wonder about the Dell hardware. Has anyone else had any problem with Dell?
     Regards, Les

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General Mach Discussion / Newbie question- using PM-DC motor as servo

« on: September 20, 2010, 07:15:32 PM »

I may be asking a ridiculous question, but could a pair of 90 vdc PM-Brush motors with quad encoders installed be operated from MACH. I know that a stepper motor is supposed to synchronize a specific turn angle per pulse, but have not figured out how a servo is kept synchronised. I thought that it was simply turned on till the encoder count matched the proper travel, but in reading the MACH manual I see all this talk of step pulses and such and am totally confused. Since a straight dc motor will turn a given distance entirely dependent on current, drag, pulse length and so many other variables, how is it actually being synchronized to a digital count. Do the step pulses continue until the encoder reaches a predetermined count based on the exact coordinates programmed into the tool track, or would changes in speed and drag potentially cause the motor to stop travel in an unsynchronized position. Also since these particular motors are high voltage/current and controllers like the gecko can't operate at those limits I suppose standard scr motor drives would have to be employed. In this case how would they be affected by a pulse based drive signal? If anyone has attempted this and found a solution a block diagram and material list would be of great assistance in assessing how to proceed. Thanks, Les