On Tuesday, November 08, 2011 11:10:12 AM andy pugh did opine: > On 8 November 2011 11:16, James Louis <[email protected]> wrote: > > Good morning all, > > There is an ad running in Digital Machinist magazine for an RC speed > > control of a brushless motor with ESC. If interested go to > > www.logicnc.com It gives EMC2 a way to control spindle speed from the > > parallel port. I haven't used one yet though. > > It isn't strictly necessary. As the RC pulse protocol is a 1 - 2mS > pulse every 20mS the standard EMC2 PWM function can be used, but gives > fairly poor resolution. (20 discrete steps with a 25,000nS base > thread).
My experience with this sort of a control scheme is limited to the pico- power gizmo's used to rotate the receiving antenna in the feedhorn of a polarotor in a satellite dish, now gone largely out of style because most are no longer motorized, but aimed at fixed birds today. These devices are not speed demons, but positioning servo's and in good condition are about a degree accurate. They can turn about 345 degrees in perhaps 1 second. Given the limitations of the base thread defined, 2 questions come to mind, the first being just how important is it to control a spindles speed to 1 or 2% accuracy? In my admittedly limited use, I either set the speed in the gcode, or by hand from the knob, trying to select a speed which is anti-resonant with the rest of the rubber in my micromills frame, often mathematically and theoretically way too high, and the chips are dangerously fine. Bit life is of course reduced in terms of weight of swarf removed with a given bit. So bit cost for me is 4x what a good stiff mill would be. But that's just me & my toy machine. I've been toying with buying a BF20/GO704 to get a bigger envelope, but I fear it would be a repeat problem given that machines lack of mass, that post is about 1/3rd the cross section it probably needs to be IMNSHO. Secondarily, it finer control is needed, then I'd suggest an additional bit of logic which would need a 2nd parport pin to control, so the pin usage is the same as my PMDX-106 setup which allows drive in either direction starting at about 30 rpm, but at 30 rpm there is no usable torque. At 250, yes, full blow the fuse torque can be had. To do this, fab a 16 bit counter with a countup input and a countdown input. Powerup reset to $0000. Feed the counters state to a 16 bit d/a, and use that to set the timing of a 555 circuit to feed the ESC, using the 1 to 2 ms variable std timebase for such. Needless complexity for a limited utility IMO. The hal setup would be the number of pulses to send to achieve the minimum speed, and the number to send to achieve maximum speed, and the offset, all scaled. If the speed is to be reduced, send n pulses to the downcount pin. Keep track of pulses sent, and send that many downcounts for a full stop. I think this could be an interesting method and reasonably economical, for an engraving gantry machine, but less so for the more conventional 3 or 4 axis small mill that may have anything from a stick of poplar to a 1.5" diameter chunk of mine shafting on its table. 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> You've been telling me to relax all the way here, and now you're telling me just to be myself? -- The Return of the Secaucus Seven ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
