On Monday 10 March 2008, Kirk Wallace wrote: >On Mon, 2008-03-10 at 12:55 -0400, Gene Heskett wrote: >> On Monday 10 March 2008, Kirk Wallace wrote: > >...snip > >> No, it can serve to absorb it, quite well from my experiences so far. >> Common sense says the weight of the damper will lower that frequency >> somewhat also. > >... snip > >Yes, I agree. I must have gotten up on the dumb side of the bed today. > No comment, been there, bought the T-shirt for 4x what it was worth. :)
>> >I also noticed >> >from other threads, that the voltage the stepper is driven with can >> >change the resonance frequency. >> >> Yes, the higher the voltage, within limits the stiffer it will be in that >> rpm range where the inductance of the motor is costing it torque. Below >> that range it should be a wash cuz the driver is chopper regulating the >> current and therefore the strength of the magnetic spring action. >> >> >I think the ideal would be to move the >> >resonance above the maximum operating speed, so you never see it in >> >normal operation. > >I should have said, move the resonance down. (or convert to heat or >something else as you mention above.) > Which to a small degree, is what the dampers do. I believe just as important is the energy recovery of the flywheel effect of the loosely coupled weight wanting to continue fwd when the motor has overshot its position and wants to spring back, the spring of the rubber washers being pushed forward by the fender washers then gives enough energy back to stop the motor on position much more quickly. Or at least that 'sequence of events' makes sense to this old fart. :) >> That would take a new concept in current profile control, and even then >> may not work well as the spikes of high current that would imply might be >> high enough to demagnetize the rotor, and effectively reduce its power >> forever. >> >> >Isn't micro stepping the most effective tool against >> >resonance? >> >> Yes, the finer the better although going beyond 8 steps does seem to be an >> area of diminishing returns. >> >> >Or maybe an RC filter on the driver outputs to help shape the >> >voltage. >> >> Absolutely not. The inrush currents in any capacitance would quickly >> overheat and destroy the H bridge components in the output stage, and any >> resistance there is pure power loss. We are cautioned to not even hook a >> scope probe to a motor lead because of its added capacitance. > >Ops, another mistake. What I was trying to say is, there might be widely >different ways to change the output signal shape. > With decent drivers, the output signal shape voltagewise is a rail to rail square wave at whatever the chopper frequency is, effectively pwm'd by the chopping action to maintain the setpoint current. >> >Of course EMC is flexible enough to be able to set up some sort >> >of feedback to mechanically or electrically change the stepping >> >characteristics. >> >> There are others here who can describe the sharpness of the stones in that >> path far better than I. I'll only say its a rocky road. :) >> >> >Brushless DC motors are just low pole count steppers aren't they? I >> >wonder if a stepper driver could be used to drive a BLDC? Though I >> >suppose a BLDC driver might be better. >> >> And that is another area I'll invite others to comment on. >> >> -- >> Cheers, Gene > >Thanks. I knew there was a reason I keep yuz guys around. Grin. Thanks. Now, if I could get some answers to my instant problems, the IRC channel seems pretty dead this afternon. But I'll make a seperate post of it. -- 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) Higher education helps your earning capacity. Ask any college professor. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
