Driver for very small brushless DC motors?
in [Design]
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From: John Devereux on 23 Nov 2009 14:08 Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> writes: > John Larkin wrote: >> On Mon, 23 Nov 2009 01:24:46 -0500, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> My processing algorithm will probably be something like this: >>> (1) Count the fringes from the time they become visible till the time >>> they go away; >>> (2) Estimate the deceleration rate by comparing the transition rates in >>> patches at the two ends of the pattern, and maybe a few pairs of patches >>> in between, which gives the deceleration curve; >>> (3) Knowing the wavelength and path length vs time (because we do by >>> now), estimate the other things we care about. >>> >>> No big huge FFTs, I don't think. That could be grim on a PIC! (On the >>> other hand, it doesn't matter if it takes 5 seconds or so to do the >>> measurement.) >>> >>> Cheers >>> >>> Phil Hobbs >> >> Pass the raw data to a PC and do it there? > > > That would be quite possible, and the prototype will certainly be done > that way, via the HP 35665A and Prologix. I'd love the actual > instrument to be lighter weight than that, though--more like a Fluke > 87, which you can shove in a drawer for a year, then pull it out and > it just works. > >> >> We're starting to use an NXP uP, ARM architecture, 280 MHz or some >> such, that has a floating-point vector co-processor. About $7. >> >> John > > My hope would be that this could be done with a 16-bit PIC and some > SPI-attached SRAM, or something like that--battery-powered, anyway. > > Do those NXPs have power control features that are reasonably easy to > use? Being able to crank it up to full speed (which I assume means a > watt or so) 1% of the time would be great. John's probably talking about the LPC3000 series, e.g. <http://www.nxp.com/#/pip/pip=[pip=LPC3220_30_40_50_1]|pp=[t=pip,i=LPC3220_30_40_50_1]> It's an ARM9, 266Mhz. At 208 MHz, the datasheet says 80mA @ 1.2V core voltage. These sort of chips tend to have very good power control. > A nice development system, a good library, and a decent display would > really help. Does it run COMMAND.COM? ;) (I'd happily settle for bash > over telnet.) They have a good development ecosystem (free and non-free) and I believe a linux distribution is available. It's BGA and you'll need external SDRAM+flash though. I am normally a strong advocate of the free GNU tools, but if you especially want to do heavy duty floating point work you would likely save time going with the official ARM (Keil) compiler. [...] -- John Devereux
From: Michael Wieser on 24 Nov 2009 14:58 On Mon, 23 Nov 2009 19:08:38 +0000, John Devereux <john(a)devereux.me.uk> wrote: >Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> writes: > >> John Larkin wrote: >>> On Mon, 23 Nov 2009 01:24:46 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>> My processing algorithm will probably be something like this: >>>> (1) Count the fringes from the time they become visible till the time >>>> they go away; >>>> (2) Estimate the deceleration rate by comparing the transition rates in >>>> patches at the two ends of the pattern, and maybe a few pairs of patches >>>> in between, which gives the deceleration curve; >>>> (3) Knowing the wavelength and path length vs time (because we do by >>>> now), estimate the other things we care about. >>>> >>>> No big huge FFTs, I don't think. That could be grim on a PIC! (On the >>>> other hand, it doesn't matter if it takes 5 seconds or so to do the >>>> measurement.) >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Pass the raw data to a PC and do it there? >> >> >> That would be quite possible, and the prototype will certainly be done >> that way, via the HP 35665A and Prologix. I'd love the actual >> instrument to be lighter weight than that, though--more like a Fluke >> 87, which you can shove in a drawer for a year, then pull it out and >> it just works. >> >>> >>> We're starting to use an NXP uP, ARM architecture, 280 MHz or some >>> such, that has a floating-point vector co-processor. About $7. >>> >>> John >> >> My hope would be that this could be done with a 16-bit PIC and some >> SPI-attached SRAM, or something like that--battery-powered, anyway. >> >> Do those NXPs have power control features that are reasonably easy to >> use? Being able to crank it up to full speed (which I assume means a >> watt or so) 1% of the time would be great. > >John's probably talking about the LPC3000 series, e.g. > ><http://www.nxp.com/#/pip/pip=[pip=LPC3220_30_40_50_1]|pp=[t=pip,i=LPC3220_30_40_50_1]> > >It's an ARM9, 266Mhz. At 208 MHz, the datasheet says 80mA @ 1.2V core >voltage. These sort of chips tend to have very good power control. > >> A nice development system, a good library, and a decent display would >> really help. Does it run COMMAND.COM? ;) (I'd happily settle for bash >> over telnet.) > >They have a good development ecosystem (free and non-free) and I believe >a linux distribution is available. It's BGA and you'll need external >SDRAM+flash though. > >I am normally a strong advocate of the free GNU tools, but if you >especially want to do heavy duty floating point work you would likely >save time going with the official ARM (Keil) compiler. > >[...] http://www.embeddedartists.com/ - Michael Wieser --
From: Michael Wieser on 24 Nov 2009 15:05 On Sun, 22 Nov 2009 15:48:00 -0500, 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 Toshiba TB6588FG - Michael Wieser --
From: JosephKK on 1 Dec 2009 23:45 On Mon, 23 Nov 2009 00:49:03 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >dagmargoodboat(a)yahoo.com wrote: >> On Nov 23, 12:07 am, Phil Hobbs wrote: >>> dagmargoodb...(a)yahoo.com wrote: >>>> On Nov 22, 9:06 pm, Phil Hobbs wrote: >> >>>>> I'm actually just going to spin it up and do the measurement as it spins >>>>> down unpowered. That way I should have zero cogging and no jitter due >>>>> to commutation. >>> >>>> The unpowered motor will still cog of course, just not nearly as much. >>> >>>> For just testing VCR spindles might be interesting. They're an >>>> endangered species now, but they're 3-phase BLDC motors, with >>>> integrated drivers, flywheels, and impressively low run-out bearings. >>>> That level of precision& longevity has got to imply a certain >>>> smoothness of rotation& lack of vibration too. Couldn't hurt, >>>> anyhow. >>> >>>> Probably kid stuff by your standards. >>> >>>> -- >>>> Cheers, >>>> James Arthur >>> >>> There are no iron teeth (or any other iron) in the rotor, so when it's >>> unpowered, the only things left to cause angular acceleration are the >>> bearings, the slip rings, air friction, and probably some slight eddy >>> current loss due to remanent magnetization. They call it 'zero >>> cogging'. Whether it's close enough to zero, I'm not sure. >> >> I was thinking both eddies and modulation of aerodynamic drag by / at >> the poles. >> >> Also, even completely electrically open, the rotor poles form L-C >> tanks with their winding capacitances. I've no idea how much those >> will matter, but they'll suck a little energy at each pole crossing, >> and kick or drag, depending. >> >> >> -- >> Cheers, >> James Arthur > >True, but hopefully a small effect at a few hundred RPM--they'll be very >far from resonance. > >After all that build-up, I'd better go take some data, or people will >start thinking I'm like that guy who used to brag all over Usenet about >making diamonds by the pound... > >Cheers > >Phil Hobbs Hey, i still vote for the flywheel.
From: JosephKK on 1 Dec 2009 23:57
On Sun, 22 Nov 2009 23:11:09 -0800 (PST), dagmargoodboat(a)yahoo.com wrote: >On Nov 23, 1:08 am, Phil Hobbs ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> dagmargoodb...(a)yahoo.com wrote: >> > On Nov 23, 12:42 am, Phil Hobbs wrote: >> >> dagmargoodb...(a)yahoo.com wrote: >> >> >>> Phil's app sounds like it needs a 1,000,000 line optical encoder (or a >> >>> 100,000 line analog encoder and a 14-bit a/d)! >> >> >> Nah, just Newton's laws and good timing accuracy, hopefully. I used to >> >> pal around with a guy named Ed Yarmchuk, who invented self-servowriting >> >> for hard disks--he replaced insane laser interferometer spin-stands for >> >> writing the servo tracks, with a bit of drive firmware, good timing, and >> >> Mr. Newton. You couldn't make terabyte hard disks without it. He >> >> retired a year or so ago (very young). Smart guy. >> >> > Well shoot, if inertia's fair, the prototype's easy: VCR spindle with >> > a single optical stripe... >> >> Interesting idea. I need something with a flattish top, that I can >> attach some various bits and pieces to (in order to do the measurements). >> >> I've actually never taken a VCR apart in my life, I'm ashamed to say. >> (I've also hardly ever used one, except to show Veggie Tales to a Sunday >> school class once in a great while.) >> >> What sort of bearings do they use? > >Ball bearings: super-fine, and low friction. Any wobble trashes the >video, as you can imagine. I've got a few and couldn't detect any >runout at all. Mr. Google says some VCRs use a bronze(?) sleeve on a >steel post--I haven't seen any of those, but they can be very good >too--and fluid dynamic pressure bearings, e.g. http://www.freepatentsonline.com/4972283.html. Not the lowest friction bearing but certainly smooth during useful life. > >For that matter an old hard drive spindle might work pretty well too; >they've got super bearings. > >Oh, and you could use more than one stripe--maybe one index stripe for >repeatable positioning pickup, and a separate band of however many not- >as-accurately-spaced stripes for speed control feedback. |