On Thursday, December 29, 2011 09:13:26 AM Ed Nisley did opine: > On Wed, 2011-12-28 at 12:03 -0500, gene heskett wrote: > > There are hall effect based ammeters > > A while back, I mooched a Tek Hall-effect current probe from my buddy > Eks to take some interesting pix: > > http://softsolder.com/2011/06/20/stepper-sync-wheel-current-waveform-fir > st-light/ > http://softsolder.com/2011/06/27/stepper-motor-winding-current-rise-tim > e/ > > The winding current stays within a skosh of the setpoint for each > microstep, which the driver determines by applying the sine & cosine of > the microstep (electrical) angle to the overall peak current setpoint. > > That may also contribute to the mystical 70% derating factor, because in > full-step mode the driver (well, Allegro drivers, anyway) applies > 1/sqrt(2) = 0.71 of the peak current setpoint to *each* winding. That > keeps the overall motor power dissipation the same, but the total > current into both windings is 2*(1/sqrt(2))*peak = 1.4*peak. Perhaps the > person who first stated that factor, back in the dim past, forgot about > the current in the *other* winding? > > While I was doing that, I managed to stoke a mechanical resonance that > back-drove the winding current something awful: > > http://softsolder.com/2011/09/12/stepper-dynamometer-mechanical-resonanc > e/ > > Keeps me off the streets at night... [grin]
Thanks Ed. As usual, to the point on several subjects. 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> Ask not for whom the telephone bell tolls... if thou art in the bathtub, it tolls for thee. ------------------------------------------------------------------------------ Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a complex infrastructure or vast IT resources to deliver seamless, secure access to virtual desktops. With this all-in-one solution, easily deploy virtual desktops for less than the cost of PCs and save 60% on VDI infrastructure costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
