I know that someone who works, or has worked, on hard drives lurks here. I'm trying to re-purpose a hard drive head motor into a science demo. It appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns of enameled wire fits into .09", at any rate), with a circumference of around 1.4". That works out to a total length of 90", and a resistance of 1 ohm or so. Yet the measured resistance of the coil is 15 ohms. Might there be some reason to intentionally add resistance to the coil, (buried where I can't see it), or is my math just cracked today? Also -- some control guys swear by embedding a shorted coil in their torquer motors. Is that common practice in the disk drive world? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Hard drive head motor question
Started by ●May 8, 2016
Reply by ●May 8, 20162016-05-08
Tim Wescott wrote:> I know that someone who works, or has worked, on hard drives lurks here. > > I'm trying to re-purpose a hard drive head motor into a science demo. It > appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns > of enameled wire fits into .09", at any rate), with a circumference of > around 1.4". That works out to a total length of 90", and a resistance > of 1 ohm or so. > > Yet the measured resistance of the coil is 15 ohms. > > Might there be some reason to intentionally add resistance to the coil, > (buried where I can't see it), or is my math just cracked today?it is likely aluminum wire, to cut mass for faster seeking. Seek time is a published parameter, and all the drive makers try to make them go faster. Jon
Reply by ●May 8, 20162016-05-08
On Sunday, May 8, 2016 at 2:52:56 PM UTC-7, Tim Wescott wrote:> I know that someone who works, or has worked, on hard drives lurks here. > > I'm trying to re-purpose a hard drive head motor into a science demo. It > appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns > of enameled wire fits into .09", at any rate), with a circumference of > around 1.4". That works out to a total length of 90", and a resistance > of 1 ohm or so. > > Yet the measured resistance of the coil is 15 ohms. > > Might there be some reason to intentionally add resistance to the coil, > (buried where I can't see it), or is my math just cracked today? > > Also -- some control guys swear by embedding a shorted coil in their > torquer motors. Is that common practice in the disk drive world? > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.comConstant Current?
Reply by ●May 8, 20162016-05-08
On Sun, 8 May 2016 17:16:14 -0700 (PDT), Mark DeArman <s.d.m@ieee.org> wrote:>On Sunday, May 8, 2016 at 2:52:56 PM UTC-7, Tim Wescott wrote: >> I know that someone who works, or has worked, on hard drives lurks here. >> >> I'm trying to re-purpose a hard drive head motor into a science demo. It >> appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns >> of enameled wire fits into .09", at any rate), with a circumference of >> around 1.4". That works out to a total length of 90", and a resistance >> of 1 ohm or so. >> >> Yet the measured resistance of the coil is 15 ohms. >> >> Might there be some reason to intentionally add resistance to the coil, >> (buried where I can't see it), or is my math just cracked today? >> >> Also -- some control guys swear by embedding a shorted coil in their >> torquer motors. Is that common practice in the disk drive world? >> >> -- >> >> Tim Wescott >> Wescott Design Services >> http://www.wescottdesign.com > >Constant Current?Lol, I really hate google groups. I ment to delete that and change it to 'current source approximation'? It is a lorenz motor. But I sloppy moused the post button instead. Mark
Reply by ●May 9, 20162016-05-09
In article <gaSdnV7-v86pKLLKnZ2dnUU7-UudnZ2d@giganews.com>, Tim Wescott <seemywebsite@myfooter.really> wrote:> I know that someone who works, or has worked, on hard drives lurks here. > > I'm trying to re-purpose a hard drive head motor into a science demo. It > appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns > of enameled wire fits into .09", at any rate), with a circumference of > around 1.4". That works out to a total length of 90", and a resistance > of 1 ohm or so. > > Yet the measured resistance of the coil is 15 ohms. > > Might there be some reason to intentionally add resistance to the coil, > (buried where I can't see it), or is my math just cracked today? > > Also -- some control guys swear by embedding a shorted coil in their > torquer motors. Is that common practice in the disk drive world?15 Ohms sounds wrong. Those heads need to move REALLY fast and 12V doesn't put much power into 15 Ohms. 15 Ohms might be right for the head. Maybe it's the wrong wires? -- I will not see posts from astraweb, theremailer, dizum, or google because they host Usenet flooders.
Reply by ●May 9, 20162016-05-09
On 08/05/2016 22:52, Tim Wescott wrote:> I'm trying to re-purpose a hard drive head motor into a science demo. It > appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns > of enameled wire fits into .09", at any rate), with a circumference of > around 1.4". That works out to a total length of 90", and a resistance > of 1 ohm or so. > > Yet the measured resistance of the coil is 15 ohms.Could the metallic wire be much thinner than you think because the enamel thickness is much greater than usual? piglet
Reply by ●May 9, 20162016-05-09
piglet <erichpwagner@hotmail.com> wrote:>Could the metallic wire be much thinner than you think because the >enamel thickness is much greater than usual?Great hypothesis. Or maybe the wire isn't copper, for some reason. S.
Reply by ●May 9, 20162016-05-09
On Sun, 08 May 2016 16:52:52 -0500, Tim Wescott <seemywebsite@myfooter.really> wrote:>I know that someone who works, or has worked, on hard drives lurks here. > >I'm trying to re-purpose a hard drive head motor into a science demo. It >appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns >of enameled wire fits into .09", at any rate), with a circumference of >around 1.4". That works out to a total length of 90", and a resistance >of 1 ohm or so. > >Yet the measured resistance of the coil is 15 ohms. > >Might there be some reason to intentionally add resistance to the coil, >(buried where I can't see it), or is my math just cracked today? > >Also -- some control guys swear by embedding a shorted coil in their >torquer motors. Is that common practice in the disk drive world?I don't suppose it's like those transformer winding where they use a heavier gage for the external leads, with a much smaller gage just under the paper skin? Best regards, Bob Masta DAQARTA v9.20 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE 8-channel Signal Generator, DaqMusiq generator Science with your sound card!
Reply by ●May 9, 20162016-05-09
In sci.electronics.design piglet <erichpwagner@hotmail.com> wrote:> On 08/05/2016 22:52, Tim Wescott wrote: >> I'm trying to re-purpose a hard drive head motor into a science demo. It >> appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 turns >> of enameled wire fits into .09", at any rate), with a circumference of >> around 1.4". That works out to a total length of 90", and a resistance >> of 1 ohm or so. >> >> Yet the measured resistance of the coil is 15 ohms. > > Could the metallic wire be much thinner than you think because the > enamel thickness is much greater than usual?A single strand of voice coil actuator wire from my drive measures 35 AWG. 5X magnification reveals an unknown amount of residual enamel on the wire. The length of the wire is ~4900 mm with a resistance of ~11 ohm. The resistance of 35 AWG copper is 1.08 Ohm/m [1]. The theoretical resistance of 4900 mm of 35 AWG copper is ~5.3 ohms, or about half of the measured resistance. A reverse lookup of the measured resistance of ~2.2 Ohm/m yields ~38 AWG from the table. The possible use of copper-clad aluminum magnet wire [2] may also explain part the difference. Note. 1. http://www.daycounter.com/Calculators/AWG.phtml 2. http://preview.tinyurl.com/zujeg4o -- Don Kuenz KB7RPU
Reply by ●May 9, 20162016-05-09
On Sun, 08 May 2016 22:58:17 -0700, Kevin McMurtrie wrote:> In article <gaSdnV7-v86pKLLKnZ2dnUU7-UudnZ2d@giganews.com>, > Tim Wescott <seemywebsite@myfooter.really> wrote: > >> I know that someone who works, or has worked, on hard drives lurks >> here. >> >> I'm trying to re-purpose a hard drive head motor into a science demo. >> It appears to have 64 turns of #30 or #31 (or metric equivalent -- 9 >> turns of enameled wire fits into .09", at any rate), with a >> circumference of around 1.4". That works out to a total length of 90", >> and a resistance of 1 ohm or so. >> >> Yet the measured resistance of the coil is 15 ohms. >> >> Might there be some reason to intentionally add resistance to the coil, >> (buried where I can't see it), or is my math just cracked today? >> >> Also -- some control guys swear by embedding a shorted coil in their >> torquer motors. Is that common practice in the disk drive world? > > 15 Ohms sounds wrong. Those heads need to move REALLY fast and 12V > doesn't put much power into 15 Ohms. > > 15 Ohms might be right for the head. Maybe it's the wrong wires?Those are the wires whose voltage wiggles when I move the coil in the magnetic field. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
