Driver for very small brushless DC motors?
in [Design]
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From: osr on 22 Nov 2009 17:08 Phil, From research I'm doing for a similar but slower project. ATMEL APP NOTE AVR843 Microchip App Note 857 Any model airplane ESC http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=71674&start=20 I've got a very similar problem right now, except I need to microstep a stalled 3 amp 3 phase brushless motor for controlled torque in a feedback loop. Steve Roberts
From: Phil Hobbs on 22 Nov 2009 17:13 langwadt(a)fonz.dk wrote: langwadt(a)fonz.dk wrote: -- 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 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 Probably 100 mA--500 at most. Cheers 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: Phil Hobbs on 22 Nov 2009 17:43 John Larkin wrote: > 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? I'm mostly interested in very smooth motion at small scales, which is why I want an ironless BLDC. The gizmo's operation will require a lot of curve fitting to pull out the amplitude and phase of a small-amplitude tone burst of about 10k cycles over about 5 degrees of shaft rotation, once per rev. Any cogging or other bad behaviour of the motor will cause nasty spurious peaks in the spectrum, among other problems. Steppers are never sufficiently well made to avoid periodic errors--I'm at the level where I have to worry about whether the ball bearings are smooth enough, or whether I need to use jewels, which would be fragile and expensive enough to dim my enthusiasm quite a bit. (A galvo is another possibility, but those cost the Earth.) My hope is that because the balls' motion doesn't have the same period as the shaft rotation, I can sort out the bearing junk from the desired signal. In the real system, I'm expecting to have optical clues as to what the actual motor phase is, but I'm not too worried about that at this point. I'm currently gearing up to do a sanity test with a nice Maxon brush motor from my junk box, a He-Ne, and an HP 35665A dynamic signal analyzer to do the data acq and so on. (I just got a Prologix GPIB-Ethernet gizmo, so I don't have to use the floppy drive to get data in and out.) Cheers 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: dagmargoodboat on 22 Nov 2009 20:23 On Nov 22, 5:43 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > John Larkin wrote: > > > 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? > > I'm mostly interested in very smooth motion at small scales, which is > why I want an ironless BLDC. The gizmo's operation will require a lot > of curve fitting to pull out the amplitude and phase of a > small-amplitude tone burst of about 10k cycles over about 5 degrees of > shaft rotation, once per rev. Any cogging or other bad behaviour of the > motor will cause nasty spurious peaks in the spectrum, among other problems. > > Steppers are never sufficiently well made to avoid periodic errors--I'm > at the level where I have to worry about whether the ball bearings are > smooth enough, or whether I need to use jewels, which would be fragile > and expensive enough to dim my enthusiasm quite a bit. (A galvo is > another possibility, but those cost the Earth.) My hope is that because > the balls' motion doesn't have the same period as the shaft rotation, I > can sort out the bearing junk from the desired signal. > > In the real system, I'm expecting to have optical clues as to what the > actual motor phase is, but I'm not too worried about that at this point. > > I'm currently gearing up to do a sanity test with a nice Maxon brush > motor from my junk box, a He-Ne, and an HP 35665A dynamic signal > analyzer to do the data acq and so on. (I just got a Prologix > GPIB-Ethernet gizmo, so I don't have to use the floppy drive to get data > in and out.) > > Cheers > > Phil Hobbs Even microstepped, steppers shake, rattle, & roll. And they sing (resonate). I never imagined how much until I tried a few. As far as COTS, CD, DVD & hard disk spindle motor drivers? They use 3- phase BLDC motors & integrated controllers. Here's an old BLDC datasheet off ye old hard drive: http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC34929 But won't you be wanting ultra-fine control over commutation, PWM, position-interpolation and such? You'll probably have to do that yourself. Atmel, Microchip, and Freescale all have good application notes on BLDC-driving with uCs. e.g. Atmel AVR444: Sensorless control of 3-phase brushless DC motors. -- Cheers, James Arthur
From: Phil Hobbs on 22 Nov 2009 21:06
dagmargoodboat(a)yahoo.com wrote: > On Nov 22, 5:43 pm, Phil Hobbs > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> John Larkin wrote: >> >> > 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? >> >> I'm mostly interested in very smooth motion at small scales, which is >> why I want an ironless BLDC. The gizmo's operation will require a lot >> of curve fitting to pull out the amplitude and phase of a >> small-amplitude tone burst of about 10k cycles over about 5 degrees of >> shaft rotation, once per rev. Any cogging or other bad behaviour of the >> motor will cause nasty spurious peaks in the spectrum, among other problems. >> >> Steppers are never sufficiently well made to avoid periodic errors--I'm >> at the level where I have to worry about whether the ball bearings are >> smooth enough, or whether I need to use jewels, which would be fragile >> and expensive enough to dim my enthusiasm quite a bit. (A galvo is >> another possibility, but those cost the Earth.) My hope is that because >> the balls' motion doesn't have the same period as the shaft rotation, I >> can sort out the bearing junk from the desired signal. >> >> In the real system, I'm expecting to have optical clues as to what the >> actual motor phase is, but I'm not too worried about that at this point. >> >> I'm currently gearing up to do a sanity test with a nice Maxon brush >> motor from my junk box, a He-Ne, and an HP 35665A dynamic signal >> analyzer to do the data acq and so on. (I just got a Prologix >> GPIB-Ethernet gizmo, so I don't have to use the floppy drive to get data >> in and out.) >> >> Cheers >> >> Phil Hobbs > > Even microstepped, steppers shake, rattle,& roll. And they sing > (resonate). I never imagined how much until I tried a few. > > As far as COTS, CD, DVD& hard disk spindle motor drivers? They use 3- > phase BLDC motors& integrated controllers. > > Here's an old BLDC datasheet off ye old hard drive: > http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC34929 > > But won't you be wanting ultra-fine control over commutation, PWM, > position-interpolation and such? You'll probably have to do that > yourself. > > Atmel, Microchip, and Freescale all have good application notes on > BLDC-driving with uCs. > > e.g. Atmel AVR444: Sensorless control of 3-phase brushless DC motors. > > -- > Cheers, > James Arthur > 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. Cheers 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 |