Paul B. Webster VK2BZC wrote: > > Mark Willis wrote: > > > ) - You know me, though, I want to know MORE, MORE, MORE I > > have a LOT of old steppers around here & will be using them for other > > uses (some of which will have to be PIC driven, and are no-where near > > as simple as his needs. > > I just feel that someone's done virtually *all* the design work to > make those things and I doubt they would have failed to optimize the > design, at least to any significant extent. IOW, you should have a 12V > motor with the appropriate driver (chip) driven in the optimal manner. > > Now, you might begrudge the current drawn by the other parts of the > disk drive electronics but of course you will have split off the capstan > motor anyway, and any components obviously unnecessary can be removed > (or disabled) and I doubt you can make any other efficiencies. Oh, sure, all true ... But, it's no FUN if I cannot breadboard it myself! > > I want to automate feeding the cats, some day, for one thing. > > Hmmm. That'll be interesting. The good thing is the cats'll tell me if the design goes awry (They're good at leading me to their food dish ) > > He wants an absolute minimal cost solution, > > Using the drive electronics is certainly that. Definitely. Just a 555 & power source... > > I also was already talking to him about half-stepping the motor, which > > I'd probably do here - but I doubt he'll do, for finer smoother > > rotation of the motor. > > Is it *really* necessary? For some things I'll be doing, later, it'd be fun, for his job, probably not May have to full step using twin windings activated at the same time, or may have to spin at 24Hz step rate with a 4:1 gear down, to get him enough torque to do what he wants to do. We'll see. > > (I've wondered - Does half-stepping give you more effective torque > > out of the same stepper? Or no effect there?) > > Mmm, various "scraps" on similar topics on this list. It seems to me > you *may* get marginally more torque by half-stepping (having adjacent > coils simultaneously energized for alternate steps) but really, the half > step from two-coils-driven to one-coil-driven must by definition be cor- > respondingly weaker than its converse. Makes sense - you can choose to always drive pairs of coils, though, for higher torque. > Assuming each step is met with limiting friction, if the one-to-two > coil transition is only just sufficient to overcome the friction, the > next half-step would be too weak to overcome that friction and the rotor > would tend to jam. A subsequent two-coil activation involves the > opposite drive on one of these coils and would have some net torque away > from the previous position, but you'd have lost resolution. I don't see > that the analysis would be much better in continuous motion with > "flywheel" effect. He'll probably gear down and increase the step rate, if he has a torque problem. > > I might scavenge driver parts off floppy boards, but want to be able > > to be independent (on some designs) of a PC power supply > > Well... The 5¹" drives use 12V motors, so you need a 12V supply for > that. If you use logic (PICs) to drive them, you need 5V. The (tiny) > steppers in many 3¸" drives use 5V of course. You can be independent of > a PC power supply, but you'll end up supplying the same voltages. And > I'm sure you have *plenty* of spare plugs on the end of RD-BK-BK-YL > leads! "Never enough", despite the dozen spare power supplies in the garage > Cheers, > Paul B.