On Monday, April 30, 2012 11:12:52 AM Kent A. Reed did opine: > On 4/28/2012 3:34 PM, gene heskett wrote: > > I tried one of mine, the stacked fender washers& rubber dampers on my > > z yesterday, but its steel core to hold all the fender washers& > > rubber added enough rotary mass I had to cut the accels in half on my > > Z to stop the stalling, which wasn't exactly what I expected. So the > > rim heavy caster wheel seems like the lessor of a rotary mass evil to > > me. > > Errm. For the same mass, a short, large-diameter cylinder has a greater > moment of inertia than a long, small-diameter one, since the moment > depends on the *square* of the distance of the bits of mass from the > axis. The rim-heavy caster wheel might turn out to be a considerably > worse evil. > And this particular one, nearly solid black, looks like teenite, and a good inch wide, would if its countering vibration happened to be near the motors natural frequency, probably make things worse if it was coupled with a solid film of elastomer so the springback wasn't lossy. Conversely, if friction coupled so that its mass could be used as an energy sink or source depending on the direction of the slippage, it would have a more useful effect on resonance damping, but would also require gentler accel's unless the motor, at the low starting speeds has sufficient torque to 'slip the clutch' at speed up to a large percentage of the resonant peak.
In adding one of the fender washer & rubber stack versions to the Z axis, I had the stack fairly snug, and found its flywheel effect, because half its mass, the steel spool they are on, is rigidly coupled, seemed to require a pretty large cut-back in the accel's. I didn't try loosening the stack. I probably should have I guess. I also found a note in the html docs about accel's when backlash comp is in use, where the STEPGEN_MAX_ACCEL should be at least 2x the TRAJ MAX_ACCEL. With this OEM screw and halfnut, its a pretty gross (over 15 thou) correction, and I was having motor stalls at the end of the backlash move, so I'll check the effect of that as I have normally only given a 10-15% headroom there. Something to be investigated. Too bad stepconfig won't run on this install, broken pipe messages instantly when a move the motor command is issued. > Also, just to be clear, it is the ability of these dampers to dissipate > mechanical energy at the excitation frequency that counts. Their raw > inertia just provides a reaction wall for such tricks as viscous clamps > and loose rattles to work against. Which translates to, if a friction clutch is being used as the dissipation control, it would work best set fairly snug with a too heavy wheel such as this one was being used. Slippage should be concentrated to the resonance frequency speed IOW. This hopefully helps to clarify my how-to thinking. Thanks Kent. The long coupling rod between the X motor and the pin in the rear of the X drive screw, also has a rotating mass that probably enters into the max accel this motor can do as its made from 5/8" stock and nominally 4" long. Following this 'train of thought' I should probably make a 'cap' that fits over the end of the screw as it now does, but is drilled to take a 1/4" rod to be used between that, and one of those slightly flexible all metal motor couplings. Those are available in 1/4" to 1/4", and that would remove several ounces of steel from the moving mass that has to be driven. That should help, and may even compensate some for the much heavier rotor in the 425. So I'll order 2 or maybe even 5 of that coupling with an eye toward eventually replacing those solid steel monsters on the mill. Those things are well over a pound each! Here, progress comes at mail order speed. :( That alone makes me deal only with those vendors who ship in usps fixed rate boxes. Typically 3 days quicker than ups here in WV. > Regards, > Kent > > > ------------------------------------------------------------------------ > ------ Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. > Discussions will include endpoint security, mobile security and the > latest in malware threats. > http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> May you have warm words on a cold evening, a full mooon on a dark night, and a smooth road all the way to your door. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
