Driver for very small brushless DC motors?
in [Design]
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From: Phil Hobbs on 22 Nov 2009 15:48 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 -- 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
From: John Larkin on 22 Nov 2009 16:12 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 What a coincidence... I've been thinking about the same problem. How about a small, cheap stepper. One could run it in microstep mode and tweak its drive waveform to get very smooth rotation; I know that works. Then couple it to the load platform through something torsionally compliant, like a spring or a rubber tube or a piece of piano wire or something. Maximize the mass of the load platform to make a mechanical lowpass filter. Over the top, but I suppose one could make a multipole rotational lowpass filter by adding mass to the motor and/or insert an intermediate mass and use two compliant couplings. I've seen Collins-type mechanical filters like this, and it resembles a microstrip lowpass filter in concept. The stepper gives exact, controllable rotational speed open-loop, which is nice. And small steppers are cheap and easy to drive. We could program one of our multichannel arbs to test some motors and find a nice pre-distorted waveform that gives smooth rotation. I think adding some third harmonic is classic here, but whatever works. How would one instrument the resulting angular rotation? Optically, I guess, or maybe drive a variable capacitor? John
From: Baron on 22 Nov 2009 16:31 Phil Hobbs 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 That sounds like the mirror motor I've seen in some laser printers. -- Best Regards: Baron.
From: langwadt on 22 Nov 2009 16:31 On 22 Nov., 21:48, Phil Hobbs <pcdhSpamMeSensel...(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 > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > hobbs at electrooptical dot nethttp://electrooptical.net
From: langwadt on 22 Nov 2009 16:32
On 22 Nov., 21:48, Phil Hobbs <pcdhSpamMeSensel...(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 > how much current is needed? -Lasse |