On Sunday 08 July 2007, Jack Ensor wrote:
>Gene Heskett wrote:
>>On Saturday 07 July 2007, Jack Ensor wrote:
>>>I have successfully upgraded an antique Bandit CNC on a Bridgeport to
>>>EMC2. I am using the Axis user interface.
>>>
>>>Some of you may recall earlier postings of mine describing the
>>>difference between the x and y dro readout on my Bridgeport versus the
>>>emc2 readout that would occur when running the demo file, axis.ngc. The
>>>difference varied from +0.0800 to -0.1000 (usually much less than these
>>>extremes).
>>>
>>>I finally found out what was causing this error by writing a g code file
>>>that oscillated the axis under test between + 8 inches and - 8 inches at
>>>a feedrate of 5 ipm. I began at a feedrate of 100% and gradually
>>>decreased it until I discovered an instability between 1.6 ipm (20
>>>stepper rpm) and 2.0 ipm (25 stepper rpm) due to stepper motor
>>>resonance. I wondered how the original system handled these resonances
>>>- maybe it was set up so that the firmware wouldn't let it operate at
>>>these speeds. I was able to cure this problem by fabricating dampers
>>>for the x and y axes. The z axis already had a damper on it from the
>>>original Bandit system.
>>>
>>>Even though no one suggested that my problem could be due to stepper
>>>motor resonance, I am ever grateful for the help that has been provided
>>>to get me going. I couldn't have done with out it. Thanks!
>>>
>>>Now all error has been eliminated and I now have a system ready to cut
>>>metal!
>>>
>>>Jack Ensor
>>
>>Great, Jack. Now, when you get a chance, draw up or describe those dampers
>>please. I'm not actually losing/gaining steps but the noise at certain
>>speeds tells me I'm not too far from doing that. The drivers I use are
>>xylotex, and if I reset from 8 microsteps to 4, the effect is worsened
>>considerably, to the point of stalls at quite reasonable speeds.
>
>Gene, I am using full step drive and am sure that micro-stepping could
>have been a solution. That would have meant that I would have to
>replace my drivers which are designed only for quadrature drive.
>I may do a magazine article on this solution and will let you know when
>that happens.
>
>Jack Ensor
>I may do a magazine article on this solution. I'll let you know
Thanks Jack. I had considered making an adaptor sleeve and re-attaching the
handwheels after removing the crank handles, but that would probably be way
to rigid, and would just lower the frequency in addition to needing smaller
accell rates. My couplings have no elastomer in them, solid steel slip yoke
u-joints that are quite heavy at about 2.5" long and 1.5" in diameter.
Probably more mass there than in the armatures of the double-stack nema 23
motors I got from Jeff at the same time I got the 3 axis xylotex kit, which
does 8 step microstepping.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
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