Driver for very small brushless DC motors?
in [Design]
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From: JosephKK on 2 Dec 2009 00:15 On Sun, 22 Nov 2009 21:29:11 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >Spehro Pefhany wrote: >Spehro Pefhany wrote: >> On Sun, 22 Nov 2009 15:48:00 -0500, the renowned Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> I have a partly-baked idea I'm exploring, for a simple laser beam >>> diagnostic tool. It needs a small brushless motor (less than 10 mm >>> diameter and 3 mm tall) with an ironless rotor. I have possible motors >>> in mind, but it seems that there are few integrated BLDC >>> controller/driver chips these days. I was going to use an Allegro >>> A8904, but it's now listed as "not recommended for new designs". :( >>> >>> I'd prefer to use a back-EMF controller rather than Hall sensors, >>> because I don't care too much about smoothness of motion during spin-up, >>> and sensorless motors are cheaper, particularly in such small sizes. >>> >>> Any recommendations for integrated BLDC controller/driver chips? >>> >>> Thanks >>> >>> Phil Hobbs >> >> Mostly seems to be uC/DSP-based designs these days rather than ASICs. >> >> >> Best regards, >> Spehro Pefhany > > >-- >Dr Philip C D Hobbs >Principal >ElectroOptical Innovations >55 Orchard Rd >Briarcliff Manor NY 10510 >845-480-2058 >hobbs at electrooptical dot net >http://electrooptical.net >> On Sun, 22 Nov 2009 15:48:00 -0500, the renowned Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> I have a partly-baked idea I'm exploring, for a simple laser beam >>> diagnostic tool. It needs a small brushless motor (less than 10 mm >>> diameter and 3 mm tall) with an ironless rotor. I have possible motors >>> in mind, but it seems that there are few integrated BLDC >>> controller/driver chips these days. I was going to use an Allegro >>> A8904, but it's now listed as "not recommended for new designs". :( >>> >>> I'd prefer to use a back-EMF controller rather than Hall sensors, >>> because I don't care too much about smoothness of motion during spin-up, >>> and sensorless motors are cheaper, particularly in such small sizes. >>> >>> Any recommendations for integrated BLDC controller/driver chips? >>> >>> Thanks >>> >>> Phil Hobbs >> >> Mostly seems to be uC/DSP-based designs these days rather than ASICs. >> > >So I'm sort of gathering. It's natural to want to save a chip when >you're controlling a lot of motors, but it's a bit of a drag for >proof-of-concept--I really just want to know whether the cogging can >really be made low enough...with an ironless rotor, there have to be >slip rings in there somewhere, to get the current to the rotor winding. > >I suppose I could use a clutch, or a long floppy belt, or even an eddy >current drive, but I'd really rather not--a little turntable attached to >the shaft of a pancake motor is much more like it. If I do need a >separate spindle, eddy current drive is probably next easiest--spin a >small magnet near the edge of a brass turntable--but that would require >a lot more mechanical fiddling than I'd like. On the other hand, it >could use a cheap little brush motor with plain bearings...I'll have to >think about it. I only need about 100-500 rpm, but it's got to be >really really smooth. > >Cheers > >Phil Hobbs Brass/bronze sleeve bearings have been traditionally used when that requirement is paramount. Millions of turntables, tape decks, and VCRs use them for that attribute. These devices also implement / take advantage of flywheel effects for the same reason.
From: ChrisQ on 2 Dec 2009 12:42
JosephKK wrote: > > Hey, i still vote for the flywheel. Reminds me of disk motors, as used in early electricity meters ?. All you need then are two or three coils around the circumference. So long as you can electronically isolate the windings on spin down, there should be negligable effect on spin down. A metal disk is easy to balance as well... Computer dat drives use a what looks like a modded camcorder mechanism, with flat rare earth magnetics on the shaft and ironless pancake coils to drive them, should you need much torque. Usually a one chip drive solution internally, though from the examples i've stripped down, often hall sensor(s) as well... Regards, Chris |