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Author Topic: Mach 3 constant pulse width or constant duty cycle?  (Read 1774 times)

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Offline g21

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Mach 3 constant pulse width or constant duty cycle?
« on: May 23, 2015, 11:11:52 AM »
Hello everybody,

I was wondering if Mach 3 has a constant pulse width for the step output pulses with varying frequency or a constant duty cycle with varying frequency for different speeds? I am having trouble with a (Chinese) USB Mach 3 controller that puts out constant duty cycle with varying frequency that upsets my stepper drivers. I checked the output on the scope and the duty cycle is always around 50%, at low frequencies from 300 Hz all the way up to 15 kHz. Pulse width is not stable also. Steppers don't run smooth and sometimes hesitate or run rough. Positioning is correct though.

Direct to Mach 3 through parallel port and BOB all is OK so I was wondering if this could be the culprit. Anybody has some screendumps from a scope showing the pulse train at different speeds?

Thanks,

G21

Offline ger21

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Re: Mach 3 constant pulse width or constant duty cycle?
« Reply #1 on: May 23, 2015, 11:57:52 AM »
Mach3 has no control over how your Chinese controller sends the pulses.
Gerry

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Offline g21

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Re: Mach 3 constant pulse width or constant duty cycle?
« Reply #2 on: May 23, 2015, 12:15:56 PM »
Ger21,

I understand that but I was wondering how Mach 3 sends the pulses so that I can compare this and see why the Chinese USB thing runs so rough. Buddy of mine has the same motors and drivers but runs the traditional set-up of Mach 3 and his are running smooth as silk.

If I have time for the drive I will drive up there and see how the pulse train looks like from Mach 3 through the parallel port. Was just wondering if anybody knows how Mach sends pulses to the motor drivers.

Thanks for your reply anyway,

G21
Mach 3 constant pulse width or constant duty cycle?
« Reply #3 on: May 23, 2015, 06:42:22 PM »
Your USB motion control board is generating its own pulses internally, it's not doing anything with the Mach3 ones.  Comparing them will not tell you much about why the USB is rough.  Are you running step and direction or step +/-?  If the former then maybe the step edge is the wrong polarity for your drivers. 


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