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Path: ...!3.us.feeder.erje.net!feeder.erje.net!weretis.net!feeder6.news.weretis.net!newsfeed.hasname.com!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!feeder.usenetexpress.com!tr1.iad1.usenetexpress.com!69.80.99.26.MISMATCH!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 07 Mar 2024 15:27:30 +0000 From: John Larkin <jl@997PotHill.com> Newsgroups: sci.electronics.design Subject: Re: Motor Speed Control Date: Thu, 07 Mar 2024 07:26:08 -0800 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: <kvmjuihgbphkol3apro6fl4hbg7e34gvhl@4ax.com> References: <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com> <us3u77$95n9$1@gonzo.revmaps.no-ip.org> <us5vgf$3egni$4@dont-email.me> <us7puf$3te18$1@dont-email.me> <us8i7u$2673$1@dont-email.me> <usad4b$ibi5$1@dont-email.me> <usbeed$s81p$1@dont-email.me> <usc42q$104da$1@dont-email.me> X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 65 X-Trace: sv3-ss385Lkl0pyFC+P+NFQHCqp3gnRX2ljeBo7PWchrvpaHO+0lidhdDDEEdYoW9X+Vl/V6O+bDH1XlV98!iViYrj9enWy3vU6fu0k1oyr+fbt1/eDsBreQrbV3gOKVQU07FvWpG/FUvTBnxTg8cKqnNK/N92Sm!lEFJtQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4419 On Thu, 7 Mar 2024 02:14:49 -0800, KevinJ93 <kevin_es@whitedigs.com> wrote: >On 3/6/24 8:05 PM, Bill Sloman wrote: >> On 7/03/2024 5:36 am, KJW93 wrote: >>> On 3/5/24 5:51 PM, Bill Sloman wrote: >>>> On 6/03/2024 5:57 am, KevinJ93 wrote: >>> ... >>>>>> >>>>>> That's not all that "old school" - Philips got a patent on it >>>>>> around the 1970's. It wasn't remotely good enough for audio work, >>>>>> and neither were centrifugal governors. Synchronous motors with >>>>>> stable frequency drives was what the old school relied on >>>>> >>>>> Philips used the negative resistance approach for speed control in >>>>> their portable cassette players - so it wasn't too bad. >>>> >>>> The feedback from a DC motor depends on the strength of the permanent >>>> magnets in the motor being regulated, and that is temperature >>>> dependent. Philips may have relied on it, but it was still ghastly. >>> >>> Obviously Philips didn't agree with you.� For a consumer product used >>> over a benign temperature range it was fine. >>> >>> The temperature coefficient was low enough to keep the tape speed >>> within 1% or so. >>> >>>>> Synchronous AC motors� weren't an option in a portable unit. >>>> >>>> Watches are portable, and electronic watches rely on a 32,768 Hz >>>> watch crystal as the frequency reference. Some of them included >>>> stepper motors to drive a mechanical display. >>>> >>>> Synchronous motors obviously are a practical option in a portable >>>> unit, though perhaps not in a really cheap one. >>> >>> At the time these devices were first designed (mid-late 60's) >>> synchronous motors weren't a practical option for a consumer item. >> >> Back then they were called "stepper motors" and would have been entirely >> practical. Admittedly, I didn't get to design one into what would have >> been a cheap product until 1978 (and at EMI Central Research) but they >> were pretty cheap. >> > >Stepper motors are much too inefficient and have too much torque ripple >for capstan drive - not at all suitable for a battery powered device, >they also tend to be noisy. Efficiency wouldn't matter for a capstain motor (they may well absorb power!) and microstepping is easy and smooth. > >Even implementing the discrete drive electronics would be more costly >than necessary at a time where individual transistors were a significant >cost; Philips' solution used two transistors - creating a divide by 4 >plus driver transistors plus an oscillator would probably require about >ten transistors plus numerous other components. > >If stepper motors would be such a great solution how come nobody has had >your insight and used them in the past sixty years for tape drives? Does anybody still make audio tape drives?