Gentlemen,

Can motor speed control ever approach the effectiveness of the old
style drive belts and pullys approach? Would simple PWM be enough or
would there be some additional trickery needed?

CD.

In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
cd@notformail.com says...
> ewsgroups: sci.electronics.design
>
> Gentlemen,
>
> Can motor speed control ever approach the effectiveness of the old
> style drive belts and pullys approach? Would simple PWM be enough or
> would there be some additional trickery needed?
>
>

When I retired about 10 years ago we had many motor speed controls that
worked very well ranging from less than 1 HP to 300 HP. Some were for
DC motors and some were for 3 phase AC motors.

Were you thinking of AC or DC motors ?

The AC motor speed controlers used a very odd waveform and sometimes the
motors would produce a sound of say 1000 Hz in frequency. The speed
controlers were microprocessed based and we had to set several
parameters depending on the motor and type of service.

They have probably gotten better in the last 10 years.

On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
<rmowery42@charter.net> wrote:

>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>cd@notformail.com says...
>> ewsgroups: sci.electronics.design
>>
>> Gentlemen,
>>
>> Can motor speed control ever approach the effectiveness of the old
>> style drive belts and pullys approach? Would simple PWM be enough or
>> would there be some additional trickery needed?
>>
>>
>
>When I retired about 10 years ago we had many motor speed controls that
>worked very well ranging from less than 1 HP to 300 HP. Some were for
>DC motors and some were for 3 phase AC motors.
>
>Were you thinking of AC or DC motors ?
>
>The AC motor speed controlers used a very odd waveform and sometimes the
>motors would produce a sound of say 1000 Hz in frequency. The speed
>controlers were microprocessed based and we had to set several
>parameters depending on the motor and type of service.
>
>They have probably gotten better in the last 10 years.

DC. This will be for an old reel-to-reel tape recorder that's been in
storage for decades. All the rubber drive belts have perished and
replacements are unobtainable. It has 3 speeds: 3 inches per second,
7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
the idea is feasible, I have a couple of other R-Rs I'd like to get
working again as well.

On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
><rmowery42@charter.net> wrote:
>
>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>cd@notformail.com says...
>>> ewsgroups: sci.electronics.design
>>>
>>> Gentlemen,
>>>
>>> Can motor speed control ever approach the effectiveness of the old
>>> style drive belts and pullys approach? Would simple PWM be enough or
>>> would there be some additional trickery needed?
>>>
>>>
>>
>>When I retired about 10 years ago we had many motor speed controls that
>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>DC motors and some were for 3 phase AC motors.
>>
>>Were you thinking of AC or DC motors ?
>>
>>The AC motor speed controlers used a very odd waveform and sometimes the
>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>controlers were microprocessed based and we had to set several
>>parameters depending on the motor and type of service.
>>
>>They have probably gotten better in the last 10 years.
>
>DC. This will be for an old reel-to-reel tape recorder that's been in
>storage for decades. All the rubber drive belts have perished and
>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>the idea is feasible, I have a couple of other R-Rs I'd like to get
>working again as well.

I saw an article somewhere that suggested one can make replacement
drive belts from strips of back-to-back Scotch tape.

The old Ampex and such tape recorders usually used AC motors.

On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
wrote:

>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>wrote:
>
>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>><rmowery42@charter.net> wrote:
>>
>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>cd@notformail.com says...
>>>> ewsgroups: sci.electronics.design
>>>>
>>>> Gentlemen,
>>>>
>>>> Can motor speed control ever approach the effectiveness of the old
>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>> would there be some additional trickery needed?
>>>>
>>>>
>>>
>>>When I retired about 10 years ago we had many motor speed controls that
>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>DC motors and some were for 3 phase AC motors.
>>>
>>>Were you thinking of AC or DC motors ?
>>>
>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>controlers were microprocessed based and we had to set several
>>>parameters depending on the motor and type of service.
>>>
>>>They have probably gotten better in the last 10 years.
>>
>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>storage for decades. All the rubber drive belts have perished and
>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>working again as well.
>
>I saw an article somewhere that suggested one can make replacement
>drive belts from strips of back-to-back Scotch tape.
>
>The old Ampex and such tape recorders usually used AC motors.

One of the other tape recorders I have used a 240V motor. Not sure
whether AC or DC motors are more suited to PWM control.

On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>><rmowery42@charter.net> wrote:
>>>
>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>cd@notformail.com says...
>>>>> ewsgroups: sci.electronics.design
>>>>>
>>>>> Gentlemen,
>>>>>
>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>>> would there be some additional trickery needed?
>>>>>
>>>>>
>>>>
>>>>When I retired about 10 years ago we had many motor speed controls that
>>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>>DC motors and some were for 3 phase AC motors.
>>>>
>>>>Were you thinking of AC or DC motors ?
>>>>
>>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>>controlers were microprocessed based and we had to set several
>>>>parameters depending on the motor and type of service.
>>>>
>>>>They have probably gotten better in the last 10 years.
>>>
>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>storage for decades. All the rubber drive belts have perished and
>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>working again as well.
>>
>>I saw an article somewhere that suggested one can make replacement
>>drive belts from strips of back-to-back Scotch tape.
>>
>>The old Ampex and such tape recorders usually used AC motors.
>
>One of the other tape recorders I have used a 240V motor. Not sure
>whether AC or DC motors are more suited to PWM control.

The Ampex r-r recorders, and others, used a synchronous AC motor for
the capstain drive and shaded-pole AC motors for the reels.

The takeup reel motor ran stalled, and the feed reel motor had DC
applied to make a mild drag. Cheaper recorders had a single motor and
a mess of belts and clutches and such.

My first job was as a tech in a language lab, so I learned a lot about
tape recorders. I recall that the pay was about 70 cents per hour.

AC motors don't PWM well. DC motors don't speed control well, without
some sort of feedback loop. A BLDC motor with tach could make a very
nice capstain drive, with a lot of electronics.

On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
wrote:

>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>wrote:
>
>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>><rmowery42@charter.net> wrote:
>>>>
>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>cd@notformail.com says...
>>>>>> ewsgroups: sci.electronics.design
>>>>>>
>>>>>> Gentlemen,
>>>>>>
>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>>>> would there be some additional trickery needed?
>>>>>>
>>>>>>
>>>>>
>>>>>When I retired about 10 years ago we had many motor speed controls that
>>>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>>>DC motors and some were for 3 phase AC motors.
>>>>>
>>>>>Were you thinking of AC or DC motors ?
>>>>>
>>>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>>>controlers were microprocessed based and we had to set several
>>>>>parameters depending on the motor and type of service.
>>>>>
>>>>>They have probably gotten better in the last 10 years.
>>>>
>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>storage for decades. All the rubber drive belts have perished and
>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>working again as well.
>>>
>>>I saw an article somewhere that suggested one can make replacement
>>>drive belts from strips of back-to-back Scotch tape.
>>>
>>>The old Ampex and such tape recorders usually used AC motors.
>>
>>One of the other tape recorders I have used a 240V motor. Not sure
>>whether AC or DC motors are more suited to PWM control.
>
>The Ampex r-r recorders, and others, used a synchronous AC motor for
>the capstain drive and shaded-pole AC motors for the reels.
>
>The takeup reel motor ran stalled, and the feed reel motor had DC
>applied to make a mild drag. Cheaper recorders had a single motor and
>a mess of belts and clutches and such.
>
>My first job was as a tech in a language lab, so I learned a lot about
>tape recorders. I recall that the pay was about 70 cents per hour.
>
>AC motors don't PWM well. DC motors don't speed control well, without
>some sort of feedback loop. A BLDC motor with tach could make a very
>nice capstain drive, with a lot of electronics.

Thanks, John; very interesting. What do you mean by takeup reel motor
ran stalled? And what is it that controls the speed of the tape - the
capstan/pinch-wheel motor or the relevant reel motor?

Cursitor Doom <cd@notformail.com> wrote:
> On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
> wrote:
>
>>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>>wrote:
>>>>
>>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>>><rmowery42@charter.net> wrote:
>>>>>
>>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>>cd@notformail.com says...
>>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>>> style drive belts and pullys approach? Would simple PWM be enough
>>>>>>> or would there be some additional trickery needed?
>>>>>>
>>>>>>When I retired about 10 years ago we had many motor speed controls
>>>>>>that worked very well ranging from less than 1 HP to 300 HP. Some
>>>>>>were for DC motors and some were for 3 phase AC motors.
>>>>>>
>>>>>>Were you thinking of AC or DC motors ?
>>>>>>
>>>>>>The AC motor speed controlers used a very odd waveform and sometimes
>>>>>>the motors would produce a sound of say 1000 Hz in frequency. The
>>>>>>speed controlers were microprocessed based and we had to set several
>>>>>>parameters depending on the motor and type of service.
>>>>>>
>>>>>>They have probably gotten better in the last 10 years.
>>>>>
>>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>>storage for decades. All the rubber drive belts have perished and
>>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>>working again as well.
>>>>[snip]
>>>>The old Ampex and such tape recorders usually used AC motors.
>>>
>>>One of the other tape recorders I have used a 240V motor. Not sure
>>>whether AC or DC motors are more suited to PWM control.
>>
>>The Ampex r-r recorders, and others, used a synchronous AC motor for the
>>capstain drive and shaded-pole AC motors for the reels.
>>
>>The takeup reel motor ran stalled, and the feed reel motor had DC applied
>>to make a mild drag. Cheaper recorders had a single motor and a mess of
>>belts and clutches and such. [snip] AC motors don't PWM well. DC motors
>>don't speed control well, without some sort of feedback loop. A BLDC
>>motor with tach could make a very nice capstain drive, with a lot of
>>electronics.
>
> Thanks, John; very interesting. What do you mean by takeup reel motor ran
> stalled?

The take-up motor is set to a speed (RPM) such that it maintains a tension
on the tape on the capstan/pinch-wheel. This is to assure that the tape
spools onto the take-up reel instead of unspooling on the floor. The result
is that the motor is always being held back from its desired speed (i.e.,
stalled) by the tape.

> And what is it that controls the speed of the tape - the
> capstan/pinch-wheel motor or the relevant reel motor?

The capstan and pinch-wheel controls the linear tape speed across the heads.
The take-up motor maintains tension to keep the tape spooling onto the
take-up reel, and the feed motor maintains a small back tension to prevent
the feed reel from unspooling onto the floor.

On Sun, 18 Feb 2024 23:18:44 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>>wrote:
>>>>
>>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>>><rmowery42@charter.net> wrote:
>>>>>
>>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>>cd@notformail.com says...
>>>>>>> ewsgroups: sci.electronics.design
>>>>>>>
>>>>>>> Gentlemen,
>>>>>>>
>>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>>>>> would there be some additional trickery needed?
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>When I retired about 10 years ago we had many motor speed controls that
>>>>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>>>>DC motors and some were for 3 phase AC motors.
>>>>>>
>>>>>>Were you thinking of AC or DC motors ?
>>>>>>
>>>>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>>>>controlers were microprocessed based and we had to set several
>>>>>>parameters depending on the motor and type of service.
>>>>>>
>>>>>>They have probably gotten better in the last 10 years.
>>>>>
>>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>>storage for decades. All the rubber drive belts have perished and
>>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>>working again as well.
>>>>
>>>>I saw an article somewhere that suggested one can make replacement
>>>>drive belts from strips of back-to-back Scotch tape.
>>>>
>>>>The old Ampex and such tape recorders usually used AC motors.
>>>
>>>One of the other tape recorders I have used a 240V motor. Not sure
>>>whether AC or DC motors are more suited to PWM control.
>>
>>The Ampex r-r recorders, and others, used a synchronous AC motor for
>>the capstain drive and shaded-pole AC motors for the reels.
>>
>>The takeup reel motor ran stalled, and the feed reel motor had DC
>>applied to make a mild drag. Cheaper recorders had a single motor and
>>a mess of belts and clutches and such.
>>
>>My first job was as a tech in a language lab, so I learned a lot about
>>tape recorders. I recall that the pay was about 70 cents per hour.
>>
>>AC motors don't PWM well. DC motors don't speed control well, without
>>some sort of feedback loop. A BLDC motor with tach could make a very
>>nice capstain drive, with a lot of electronics.
>
>Thanks, John; very interesting. What do you mean by takeup reel motor
>ran stalled? And what is it that controls the speed of the tape - the
>capstan/pinch-wheel motor or the relevant reel motor?

The right reel was usually the takeup. It had 120 vac applied through
a power resistor, to give a gentle takeup torque. The left reel motor,
the feed side, had a little DC applied to make some viscous drag. In
rewind, the roles were reversed, full AC on the left and no drag on
the right.

Stopping, specially during rewind, was tricky. A really good deck
would seldom dump a reel of tape on the floor.

Tape speed was controlled by the capstain, with its synchronous motor.
The takeup reel motor was then forced to run at a tiny fraction is its
native speed, basically stalled.

This was a studio-grade recorder. Cheaper decks had one
non-synchronous motor that did everything.

On Sun, 18 Feb 2024 15:46:25 -0800, John Larkin <jl@997PotHill.com>
wrote:

>On Sun, 18 Feb 2024 23:18:44 +0000, Cursitor Doom <cd@notformail.com>
>wrote:
>
>>On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>>>wrote:
>>>>
>>>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>>>wrote:
>>>>>
>>>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>>>><rmowery42@charter.net> wrote:
>>>>>>
>>>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>>>cd@notformail.com says...
>>>>>>>> ewsgroups: sci.electronics.design
>>>>>>>>
>>>>>>>> Gentlemen,
>>>>>>>>
>>>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>>>>>> would there be some additional trickery needed?
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>When I retired about 10 years ago we had many motor speed controls that
>>>>>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>>>>>DC motors and some were for 3 phase AC motors.
>>>>>>>
>>>>>>>Were you thinking of AC or DC motors ?
>>>>>>>
>>>>>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>>>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>>>>>controlers were microprocessed based and we had to set several
>>>>>>>parameters depending on the motor and type of service.
>>>>>>>
>>>>>>>They have probably gotten better in the last 10 years.
>>>>>>
>>>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>>>storage for decades. All the rubber drive belts have perished and
>>>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>>>working again as well.
>>>>>
>>>>>I saw an article somewhere that suggested one can make replacement
>>>>>drive belts from strips of back-to-back Scotch tape.
>>>>>
>>>>>The old Ampex and such tape recorders usually used AC motors.
>>>>
>>>>One of the other tape recorders I have used a 240V motor. Not sure
>>>>whether AC or DC motors are more suited to PWM control.
>>>
>>>The Ampex r-r recorders, and others, used a synchronous AC motor for
>>>the capstain drive and shaded-pole AC motors for the reels.
>>>
>>>The takeup reel motor ran stalled, and the feed reel motor had DC
>>>applied to make a mild drag. Cheaper recorders had a single motor and
>>>a mess of belts and clutches and such.
>>>
>>>My first job was as a tech in a language lab, so I learned a lot about
>>>tape recorders. I recall that the pay was about 70 cents per hour.
>>>
>>>AC motors don't PWM well. DC motors don't speed control well, without
>>>some sort of feedback loop. A BLDC motor with tach could make a very
>>>nice capstain drive, with a lot of electronics.
>>
>>Thanks, John; very interesting. What do you mean by takeup reel motor
>>ran stalled? And what is it that controls the speed of the tape - the
>>capstan/pinch-wheel motor or the relevant reel motor?
>
>The right reel was usually the takeup. It had 120 vac applied through
>a power resistor, to give a gentle takeup torque. The left reel motor,
>the feed side, had a little DC applied to make some viscous drag. In
>rewind, the roles were reversed, full AC on the left and no drag on
>the right.
>
>Stopping, specially during rewind, was tricky. A really good deck
>would seldom dump a reel of tape on the floor.
>
>Tape speed was controlled by the capstain, with its synchronous motor.
>The takeup reel motor was then forced to run at a tiny fraction is its
>native speed, basically stalled.
>
>This was a studio-grade recorder. Cheaper decks had one
>non-synchronous motor that did everything.

Very clear explanation, John; many thanks indeed for that.
The two main decks I'd like to get working again are both Ferrograph
ones, so basically top the range of non-studio decks. Built like
tanks. I'm guessing each must weigh 120lbs! They had issues at the
time with rubber components disintegrating. Kind of damaged their
reputation by the end of the 1970s. A real shame, as they were
exceptionally high quality in every other respect.

On Sun, 18 Feb 2024 23:18:44 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>>wrote:
>>>>
>>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>>><rmowery42@charter.net> wrote:
>>>>>
>>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>>cd@notformail.com says...
>>>>>>> ewsgroups: sci.electronics.design
>>>>>>>
>>>>>>> Gentlemen,
>>>>>>>
>>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>>> style drive belts and pullys approach? Would simple PWM be enough or
>>>>>>> would there be some additional trickery needed?
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>When I retired about 10 years ago we had many motor speed controls that
>>>>>>worked very well ranging from less than 1 HP to 300 HP. Some were for
>>>>>>DC motors and some were for 3 phase AC motors.
>>>>>>
>>>>>>Were you thinking of AC or DC motors ?
>>>>>>
>>>>>>The AC motor speed controlers used a very odd waveform and sometimes the
>>>>>>motors would produce a sound of say 1000 Hz in frequency. The speed
>>>>>>controlers were microprocessed based and we had to set several
>>>>>>parameters depending on the motor and type of service.
>>>>>>
>>>>>>They have probably gotten better in the last 10 years.
>>>>>
>>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>>storage for decades. All the rubber drive belts have perished and
>>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>>working again as well.
>>>>
>>>>I saw an article somewhere that suggested one can make replacement
>>>>drive belts from strips of back-to-back Scotch tape.
>>>>
>>>>The old Ampex and such tape recorders usually used AC motors.
>>>
>>>One of the other tape recorders I have used a 240V motor. Not sure
>>>whether AC or DC motors are more suited to PWM control.
>>
>>The Ampex r-r recorders, and others, used a synchronous AC motor for
>>the capstain drive and shaded-pole AC motors for the reels.
>>
>>The takeup reel motor ran stalled, and the feed reel motor had DC
>>applied to make a mild drag. Cheaper recorders had a single motor and
>>a mess of belts and clutches and such.
>>
>>My first job was as a tech in a language lab, so I learned a lot about
>>tape recorders. I recall that the pay was about 70 cents per hour.

Actually, my first job was a summer thing, in a physics lab
researching Stark-effect microwave spectroscopy. I designed and built
a couple of high-voltage square wave generators. That was the first
time I saw a Tektronix scope, which was the most beautiful thing I'd
ever seen, until I discovered girls.

>>
>>AC motors don't PWM well. DC motors don't speed control well, without
>>some sort of feedback loop. A BLDC motor with tach could make a very
>>nice capstain drive, with a lot of electronics.
>
>Thanks, John; very interesting. What do you mean by takeup reel motor
>ran stalled? And what is it that controls the speed of the tape - the
>capstan/pinch-wheel motor or the relevant reel motor?

The right reel was usually the takeup. It had 120 vac applied through
a power resistor, to give a gentle takeup torque. The left reel motor,
the feed side, had a little DC applied to make some viscous drag. In
rewind, the roles were reversed, full AC on the left and no drag on
the right.

Stopping, specially during rewind, was tricky. A really good deck
would seldom dump a reel of tape on the floor.

Tape speed was controlled by the capstain, with its synchronous motor.
The takeup reel motor was then forced to run at a tiny fraction is its
native speed, basically stalled.

This was a studio-grade recorder. Cheaper decks had one
non-synchronous motor that did everything.

On Sun, 18 Feb 2024 23:47:04 GMT, Bertrand Sindri
<bertrand.sindri@yahoo.com> wrote:

>Cursitor Doom <cd@notformail.com> wrote:
>> On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
>> wrote:
>>
>>>On Sun, 18 Feb 2024 22:10:09 +0000, Cursitor Doom <cd@notformail.com>
>>>wrote:
>>>
>>>>On Sun, 18 Feb 2024 13:23:04 -0800, John Larkin <jl@997PotHill.com>
>>>>wrote:
>>>>
>>>>>On Sun, 18 Feb 2024 20:50:19 +0000, Cursitor Doom <cd@notformail.com>
>>>>>wrote:
>>>>>
>>>>>>On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
>>>>>><rmowery42@charter.net> wrote:
>>>>>>
>>>>>>>In article <qak4ti1ncqfkmihf9dvfsh5fv16l505t9s@4ax.com>,
>>>>>>>cd@notformail.com says...
>>>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>>>> style drive belts and pullys approach? Would simple PWM be enough
>>>>>>>> or would there be some additional trickery needed?
>>>>>>>
>>>>>>>When I retired about 10 years ago we had many motor speed controls
>>>>>>>that worked very well ranging from less than 1 HP to 300 HP. Some
>>>>>>>were for DC motors and some were for 3 phase AC motors.
>>>>>>>
>>>>>>>Were you thinking of AC or DC motors ?
>>>>>>>
>>>>>>>The AC motor speed controlers used a very odd waveform and sometimes
>>>>>>>the motors would produce a sound of say 1000 Hz in frequency. The
>>>>>>>speed controlers were microprocessed based and we had to set several
>>>>>>>parameters depending on the motor and type of service.
>>>>>>>
>>>>>>>They have probably gotten better in the last 10 years.
>>>>>>
>>>>>>DC. This will be for an old reel-to-reel tape recorder that's been in
>>>>>>storage for decades. All the rubber drive belts have perished and
>>>>>>replacements are unobtainable. It has 3 speeds: 3 inches per second,
>>>>>>7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
>>>>>>the idea is feasible, I have a couple of other R-Rs I'd like to get
>>>>>>working again as well.
>>>>>[snip]
>>>>>The old Ampex and such tape recorders usually used AC motors.
>>>>
>>>>One of the other tape recorders I have used a 240V motor. Not sure
>>>>whether AC or DC motors are more suited to PWM control.
>>>
>>>The Ampex r-r recorders, and others, used a synchronous AC motor for the
>>>capstain drive and shaded-pole AC motors for the reels.
>>>
>>>The takeup reel motor ran stalled, and the feed reel motor had DC applied
>>>to make a mild drag. Cheaper recorders had a single motor and a mess of
>>>belts and clutches and such. [snip] AC motors don't PWM well. DC motors
>>>don't speed control well, without some sort of feedback loop. A BLDC
>>>motor with tach could make a very nice capstain drive, with a lot of
>>>electronics.
>>
>> Thanks, John; very interesting. What do you mean by takeup reel motor ran
>> stalled?
>
>The take-up motor is set to a speed (RPM) such that it maintains a tension
>on the tape on the capstan/pinch-wheel. This is to assure that the tape
>spools onto the take-up reel instead of unspooling on the floor. The result
>is that the motor is always being held back from its desired speed (i.e.,
>stalled) by the tape.
>
>> And what is it that controls the speed of the tape - the
>> capstan/pinch-wheel motor or the relevant reel motor?
>
>The capstan and pinch-wheel controls the linear tape speed across the heads.
>The take-up motor maintains tension to keep the tape spooling onto the
>take-up reel, and the feed motor maintains a small back tension to prevent
>the feed reel from unspooling onto the floor.

Thanks, Betrand. That pretty much ties in with what I'm seeing when
it's powered up. Looks like all of them will need a pretty thorough
service to get them back into spec. A lot can go wrong in 40 years!

On Monday, February 19, 2024 at 5:52:19 AM UTC+11, Cursitor Doom wrote:
> Gentlemen,
>
> Can motor speed control ever approach the effectiveness of the old
> style drive belts and pulleys approach? Would simple PWM be enough or
> would there be some additional trickery needed?

If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.

It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.

Brushless motors work that way, but hide the details from the customer, Classical DC motors rely on the commutator for phase control. and commutators eventually wear out.

--
Bill Sloman, Sydney

On 19/02/2024 00:34, Cursitor Doom wrote:

> The two main decks I'd like to get working again are both Ferrograph
> ones, so basically top the range of non-studio decks. Built like
> tanks. I'm guessing each must weigh 120lbs! They had issues at the
> time with rubber components disintegrating. Kind of damaged their
> reputation by the end of the 1970s. A real shame, as they were
> exceptionally high quality in every other respect.

Nothing to do with what you're after, but you might find something of
eventual use here:
<http://ukhhsoc.torrens.org/makers/Ferrograph/TapeRecorders/index.html>

--

Jeff

On 2024-02-19 01:44, Anthony William Sloman wrote:
> On Monday, February 19, 2024 at 5:52:19 AM UTC+11, Cursitor Doom wrote:
>> Gentlemen,
>>
>> Can motor speed control ever approach the effectiveness of the old
>> style drive belts and pulleys approach? Would simple PWM be enough or
>> would there be some additional trickery needed?
>
> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
>
> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.

There might be a problem if this causes mechanical vibration in the
motor (maybe be audible). This vibration might affect the tape speed and
be audible in the result.

>
> Brushless motors work that way, but hide the details from the customer, Classical DC motors rely on the commutator for phase control. and commutators eventually wear out.
>

--
Cheers, Carlos.

On Mon, 19 Feb 2024 07:57:50 +0000, Jeff Layman <Jeff@invalid.invalid>
wrote:

>On 19/02/2024 00:34, Cursitor Doom wrote:
>
>> The two main decks I'd like to get working again are both Ferrograph
>> ones, so basically top the range of non-studio decks. Built like
>> tanks. I'm guessing each must weigh 120lbs! They had issues at the
>> time with rubber components disintegrating. Kind of damaged their
>> reputation by the end of the 1970s. A real shame, as they were
>> exceptionally high quality in every other respect.
>
>Nothing to do with what you're after, but you might find something of
>eventual use here:
><http://ukhhsoc.torrens.org/makers/Ferrograph/TapeRecorders/index.html>

Thanks, Jeff. Some promo stuff I've not seen before in among that lot.

On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."
<robin_listas@es.invalid> wrote:

>On 2024-02-19 01:44, Anthony William Sloman wrote:
>> On Monday, February 19, 2024 at 5:52:19?AM UTC+11, Cursitor Doom wrote:
>>> Gentlemen,
>>>
>>> Can motor speed control ever approach the effectiveness of the old
>>> style drive belts and pulleys approach? Would simple PWM be enough or
>>> would there be some additional trickery needed?
>>
>> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
>>
>> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.
>
>There might be a problem if this causes mechanical vibration in the
>motor (maybe be audible). This vibration might affect the tape speed and
>be audible in the result.

In these machines they use a heavy flywheel on the end of the capstan
roller, so that shouldn't be an issue.

On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
wrote:

>A BLDC motor with tach could make a very
>nice capstain drive, with a lot of electronics.

A BLDC motor does not really need a tach feedback. The speed
controller performs the commutation, so it already knows how fast the
motor is spinning.

Some R/C hobby BLDC controllers have a governor mode, where they keep
the motor speed constant regardless of torque.

The electronics is not complicated at all. It is essentially a
microcontroller and six MOSFETs.
--
RoRo

On Tuesday, February 20, 2024 at 12:41:56 AM UTC+11, Robert Roland wrote:
> On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <j...@997PotHill.com>
> wrote:
> >A BLDC motor with tach could make a very
> >nice capstain drive, with a lot of electronics.
>
> A BLDC motor does not really need a tach feedback. The speed
> controller performs the commutation, so it already knows how fast the
> motor is spinning.

A brushless DC motor has already got built-in shaft position sensing, so a tachometer is redundant.

If you want to control. torque as well as rotational speed, you do need to know where the rotating magnets are with respect to the static coils, and a brushless DC motor won't necessarily let you get at that information.

A tachometer just tells you how faster the motor shaft is spinning, which may not be all that you need to know.

> Some R/C hobby BLDC controllers have a governor mode, where they keep
> the motor speed constant regardless of torque.
>
> The electronics is not complicated at all. It is essentially a microcontroller and six MOSFETs.

And the hard-ware that senses where the rotating magnets are with respect to the frame, which can be pretty simple too.

--
Bill Sloman, Sydney

On Mon, 19 Feb 2024 14:41:50 +0100, Robert Roland <fake@ddress.no>
wrote:

>On Sun, 18 Feb 2024 15:00:19 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>A BLDC motor with tach could make a very
>>nice capstain drive, with a lot of electronics.
>
>A BLDC motor does not really need a tach feedback. The speed
>controller performs the commutation, so it already knows how fast the
>motor is spinning.

Most have speed that's about linearly dependent on supply voltage.
Speed droops with load. Ears are pretty sensitive to wow and flutter.

>
>Some R/C hobby BLDC controllers have a governor mode, where they keep
>the motor speed constant regardless of torque.
>
>The electronics is not complicated at all. It is essentially a
>microcontroller and six MOSFETs.

Yeah, microcontrollers are simple.

On Mon, 19 Feb 2024 13:35:58 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."
><robin_listas@es.invalid> wrote:
>
>>On 2024-02-19 01:44, Anthony William Sloman wrote:
>>> On Monday, February 19, 2024 at 5:52:19?AM UTC+11, Cursitor Doom wrote:
>>>> Gentlemen,
>>>>
>>>> Can motor speed control ever approach the effectiveness of the old
>>>> style drive belts and pulleys approach? Would simple PWM be enough or
>>>> would there be some additional trickery needed?
>>>
>>> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
>>>
>>> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.
>>
>>There might be a problem if this causes mechanical vibration in the
>>motor (maybe be audible). This vibration might affect the tape speed and
>>be audible in the result.
>
>In these machines they use a heavy flywheel on the end of the capstan
>roller, so that shouldn't be an issue.

If there's a belt, that will further lowpass filter angular vibration.

A microstepper would be a great capstain driver, but needs drive
logic, a uP with PWM blocks maybe. And a bunch of code.

That could be a product, if there's enough market for fixing up old
tape decks. A Pi Pico could be the compute engine. Micro Python would
be fast enough.

The dynamics of handling tape are non-trivial. Transitioning between
play or rewind or fast foreward, to stop, is tricky and involves state
memory.

On Sunday, February 18, 2024 at 3:50:29 PM UTC-5, Cursitor Doom wrote:
> On Sun, 18 Feb 2024 15:34:52 -0500, Ralph Mowery
> <rmow...@charter.net> wrote:
>
> >In article <qak4ti1ncqfkmihf9...@4ax.com>,
> >c...@notformail.com says...
> >> ewsgroups: sci.electronics.design
> >>
> >> Gentlemen,
> >>
> >> Can motor speed control ever approach the effectiveness of the old
> >> style drive belts and pullys approach? Would simple PWM be enough or
> >> would there be some additional trickery needed?
> >>
> >>
> >
> >When I retired about 10 years ago we had many motor speed controls that
> >worked very well ranging from less than 1 HP to 300 HP. Some were for
> >DC motors and some were for 3 phase AC motors.
> >
> >Were you thinking of AC or DC motors ?
> >
> >The AC motor speed controlers used a very odd waveform and sometimes the
> >motors would produce a sound of say 1000 Hz in frequency. The speed
> >controlers were microprocessed based and we had to set several
> >parameters depending on the motor and type of service.
> >
> >They have probably gotten better in the last 10 years.
> DC. This will be for an old reel-to-reel tape recorder that's been in
> storage for decades. All the rubber drive belts have perished and
> replacements are unobtainable. It has 3 speeds: 3 inches per second,
> 7.5 IPS and 15. I believe it's a 24V motor but will have to check. If
> the idea is feasible, I have a couple of other R-Rs I'd like to get
> working again as well.

I suggest you try these websites for replacement belts:

fixyouraudio.com
webspareparts.com
https://www.thevoiceofmusic.com/
https://www.vintage-electronics.net/
thakker.eu

On occasion, I got a belt size that was close but slightly oversized and cut it to correct size and used superglue to join the two ends
I've also got small rubber belt material from (I can't remember the place), cut it to size and joined with superglue.

Using the above resources or making my own belts, I've repaired some vintage late 1970s JVC cassette decks (KD85, KD-A7), and two prize R2R's Akai GX77 and Pioneer RT-707.

Still looking for that 'affordable' Nak Dragon....direct drive.....

good luck

On Mon, 19 Feb 2024 09:10:13 -0800, John Larkin <jl@997PotHill.com>
wrote:

>On Mon, 19 Feb 2024 13:35:58 +0000, Cursitor Doom <cd@notformail.com>
>wrote:
>
>>On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."
>><robin_listas@es.invalid> wrote:
>>
>>>On 2024-02-19 01:44, Anthony William Sloman wrote:
>>>> On Monday, February 19, 2024 at 5:52:19?AM UTC+11, Cursitor Doom wrote:
>>>>> Gentlemen,
>>>>>
>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>> style drive belts and pulleys approach? Would simple PWM be enough or
>>>>> would there be some additional trickery needed?
>>>>
>>>> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
>>>>
>>>> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.
>>>
>>>There might be a problem if this causes mechanical vibration in the
>>>motor (maybe be audible). This vibration might affect the tape speed and
>>>be audible in the result.
>>
>>In these machines they use a heavy flywheel on the end of the capstan
>>roller, so that shouldn't be an issue.
>
>If there's a belt, that will further lowpass filter angular vibration.

Very true.

>
>A microstepper would be a great capstain driver, but needs drive
>logic, a uP with PWM blocks maybe. And a bunch of code.

It's another option - albeit perhaps a last one on grounds of
complexity.

>That could be a product, if there's enough market for fixing up old
>tape decks. A Pi Pico could be the compute engine. Micro Python would
>be fast enough.

Or maybe an Arduino.

>The dynamics of handling tape are non-trivial. Transitioning between
>play or rewind or fast foreward, to stop, is tricky and involves state
>memory.

I dunno what "state memory" is, but the rest of that paragraph had
already unhappily occurred to me.

That

On Mon, 19 Feb 2024 23:18:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Mon, 19 Feb 2024 09:10:13 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>On Mon, 19 Feb 2024 13:35:58 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."
>>><robin_listas@es.invalid> wrote:
>>>
>>>>On 2024-02-19 01:44, Anthony William Sloman wrote:
>>>>> On Monday, February 19, 2024 at 5:52:19?AM UTC+11, Cursitor Doom wrote:
>>>>>> Gentlemen,
>>>>>>
>>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>>> style drive belts and pulleys approach? Would simple PWM be enough or
>>>>>> would there be some additional trickery needed?
>>>>>
>>>>> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
>>>>>
>>>>> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.
>>>>
>>>>There might be a problem if this causes mechanical vibration in the
>>>>motor (maybe be audible). This vibration might affect the tape speed and
>>>>be audible in the result.
>>>
>>>In these machines they use a heavy flywheel on the end of the capstan
>>>roller, so that shouldn't be an issue.
>>
>>If there's a belt, that will further lowpass filter angular vibration.
>
>Very true.
>
>>
>>A microstepper would be a great capstain driver, but needs drive
>>logic, a uP with PWM blocks maybe. And a bunch of code.
>
>It's another option - albeit perhaps a last one on grounds of
>complexity.
>
>>That could be a product, if there's enough market for fixing up old
>>tape decks. A Pi Pico could be the compute engine. Micro Python would
>>be fast enough.
>
>Or maybe an Arduino.
>
>>The dynamics of handling tape are non-trivial. Transitioning between
>>play or rewind or fast foreward, to stop, is tricky and involves state
>>memory.
>
>I dunno what "state memory" is, but the rest of that paragraph had
>already unhappily occurred to me.

By which I mean the prospect of several hundred feet of tape spewing
out on a sudden stop like a fucking tagliatelle factory on overtime.

mandag den 19. februar 2024 kl. 18.11.59 UTC+1 skrev John Larkin:
> On Mon, 19 Feb 2024 13:35:58 +0000, Cursitor Doom <c...@notformail.com>
> wrote:
> >On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."
> ><robin_...@es.invalid> wrote:
> >
> >>On 2024-02-19 01:44, Anthony William Sloman wrote:
> >>> On Monday, February 19, 2024 at 5:52:19?AM UTC+11, Cursitor Doom wrote:
> >>>> Gentlemen,
> >>>>
> >>>> Can motor speed control ever approach the effectiveness of the old
> >>>> style drive belts and pulleys approach? Would simple PWM be enough or
> >>>> would there be some additional trickery needed?
> >>>
> >>> If you want to control the speed and torque of a motor, chose a three phase or five phase synchronous motor, monitor where the rotor is with respect to where you want it to be, and control the phase and current through each winding to generate the torque you want. Fast pulse width modulation - quite a lot faster than the AC frequencies s being fed into the motor - will let you do that pretty precisely.
> >>>
> >>> It's complicated but not all that expensive, unless the motors are big - and tape recorders don't use big motors.
> >>
> >>There might be a problem if this causes mechanical vibration in the
> >>motor (maybe be audible). This vibration might affect the tape speed and
> >>be audible in the result.
> >
> >In these machines they use a heavy flywheel on the end of the capstan
> >roller, so that shouldn't be an issue.
> If there's a belt, that will further lowpass filter angular vibration.
>
> A microstepper would be a great capstain driver, but needs drive
> logic, a uP with PWM blocks maybe. And a bunch of code.

I doubt it, a regular stepper will be noisy