On 4/03/2024 6:45 pm, Jasen Betts wrote:
> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>> Gentlemen,
>>
>> Can motor speed control ever approach the effectiveness of the old
>> style drive belts and pulleys approach?
>
> you mean like a centrifugal governor?
>
>> Would simple PWM be enough or would there be some additional trickery
>> needed?
>
> PWM could. if you sample the back EMF during the off time of the PWM and feed
> that back to the regulator... (or read the motor speed some other way,
> you could have an interruptor typse sensor and control speed using a
> PLL)
>
> Old school when they weren't using centrifugal governors they would put
> a compensating negative resistance in series with the motor and feed
> the combination from a fixed DC voltage or fake that result.

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
--
Bill Sloman, Sydney

On a sunny day (Mon, 4 Mar 2024 07:45:43 -0000 (UTC)) it happened Jasen Betts
<usenet@revmaps.no-ip.org> wrote in <us3u77$95n9$1@gonzo.revmaps.no-ip.org>:

>On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>> Gentlemen,
>>
>> Can motor speed control ever approach the effectiveness of the old
>> style drive belts and pullys approach?
>
>you mean like a centrifugal governor?
>
>> Would simple PWM be enough or would there be some additional trickery
>> needed?
>
>PWM could. if you sample the back EMF during the off time of the PWM and feed
>that back to the regulator... (or read the motor speed some other way,
>you could have an interruptor typse sensor and control speed using a
>PLL)
>
>Oldschool when they weren't using centrifugal governors they would put
>a compensating negative resistance in series with the motor and feed
>the combination from a fixed DC voltage or fake that result.

In the old days with perfotape audio tape (for getting in sync with the 35 mm film also perforates)
we had variable frequency motor drive made with some real motor generator, later with electronics.
Special big room in teh studio for the generator
In sync with the vertical (50 Hz here) frame rate, in German:
https://www.klangfilm.org/index.php?lng=0&music=&type=0&frame=3&item=&title=Magnetocord%2016%20M/R&dir=data/documentations/electronics/tape_machines/magnetocord_16_m-r/&num=1

But as to drive belts add take up and supply reel system
long ago I had a Philips LDL1000 video tape recorder (before all that VHS and Betamax stuff,
in the days of Sony Umatic.
It was a BW recorder, modified it for color...
But look at what this picture:
https://i.ebayimg.com/images/g/w8oAAOSwI7JcwuJW/s-l1600.jpg

Note the big alu? disks under the take up and supply reels
And the smaller round 2 magnets disks in the middle
It uses magnetc coupling, so no belts.
The thing in the middle rotates fast, induction curents in the disks makes the tape sides run.
===|===
------||------ | ------||-------
===|===
|
capstan
motor
User fixed font, drawing not to scale.

On 3/4/24 6:19 PM, Bill Sloman wrote:
> On 4/03/2024 6:45 pm, Jasen Betts wrote:
>> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>>> Gentlemen,
>>>
>>> Can motor speed control ever approach the effectiveness of the old
>>> style drive belts and pulleys approach?
>>
>> you mean like a centrifugal governor?
>>
>>> Would simple PWM be enough or would there be some additional trickery
>>> needed?
>>
>> PWM could. if you sample the back EMF during the off time of the PWM
>> and feed
>> that back to the regulator... (or read the motor speed some other way,
>> you could have an interruptor typse sensor and control speed using a
>> PLL)
>>
>> Old school when they weren't using centrifugal governors they would put
>> a compensating negative resistance in series with the motor and feed
>> the combination from a fixed DC voltage or fake that result.
>
> 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. Synchronous AC motors
weren't an option in a portable unit.

Other manufacturers did use centrifugal governors.

kw

On Tue, 5 Mar 2024 10:57:18 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:

>On 3/4/24 6:19 PM, Bill Sloman wrote:
>> On 4/03/2024 6:45 pm, Jasen Betts wrote:
>>> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>>>> Gentlemen,
>>>>
>>>> Can motor speed control ever approach the effectiveness of the old
>>>> style drive belts and pulleys approach?
>>>
>>> you mean like a centrifugal governor?
>>>
>>>> Would simple PWM be enough or would there be some additional trickery
>>>> needed?
>>>
>>> PWM could. if you sample the back EMF during the off time of the PWM
>>> and feed
>>> that back to the regulator... (or read the motor speed some other way,
>>> you could have an interruptor typse sensor and control speed using a
>>> PLL)
>>>
>>> Old school when they weren't using centrifugal governors they would put
>>> a compensating negative resistance in series with the motor and feed
>>> the combination from a fixed DC voltage or fake that result.
>>
>> 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. Synchronous AC motors
>weren't an option in a portable unit.
>
>Other manufacturers did use centrifugal governors.

So did steam engines.

On 6/03/2024 5:57 am, KevinJ93 wrote:
> On 3/4/24 6:19 PM, Bill Sloman wrote:
>> On 4/03/2024 6:45 pm, Jasen Betts wrote:
>>> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>>>> Gentlemen,
>>>>
>>>> Can motor speed control ever approach the effectiveness of the old
>>>> style drive belts and pulleys approach?
>>>
>>> you mean like a centrifugal governor?
>>>
>>>> Would simple PWM be enough or would there be some additional trickery
>>>> needed?
>>>
>>> PWM could. if you sample the back EMF during the off time of the PWM
>>> and feed
>>> that back to the regulator... (or read the motor speed some other way,
>>> you could have an interruptor typse sensor and control speed using a
>>> PLL)
>>>
>>> Old school when they weren't using centrifugal governors they would put
>>> a compensating negative resistance in series with the motor and feed
>>> the combination from a fixed DC voltage or fake that result.
>>
>> 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.

> 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.

> Other manufacturers did use centrifugal governors.

Only at the very cheap and nasty end of the market.

--
Bill Sloman, Sydney

On 6/03/2024 10:11 am, Cursitor Doom wrote:
> On Tue, 5 Mar 2024 10:57:18 -0800, KevinJ93 <kevin_es@whitedigs.com>
> wrote:
>
>> On 3/4/24 6:19 PM, Bill Sloman wrote:
>>> On 4/03/2024 6:45 pm, Jasen Betts wrote:
>>>> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>>>>> Gentlemen,
>>>>>
>>>>> Can motor speed control ever approach the effectiveness of the old
>>>>> style drive belts and pulleys approach?
>>>>
>>>> you mean like a centrifugal governor?
>>>>
>>>>> Would simple PWM be enough or would there be some additional trickery
>>>>> needed?
>>>>
>>>> PWM could. if you sample the back EMF during the off time of the PWM
>>>> and feed
>>>> that back to the regulator... (or read the motor speed some other way,
>>>> you could have an interruptor typse sensor and control speed using a
>>>> PLL)
>>>>
>>>> Old school when they weren't using centrifugal governors they would put
>>>> a compensating negative resistance in series with the motor and feed
>>>> the combination from a fixed DC voltage or fake that result.
>>>
>>> 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. Synchronous AC motors
>> weren't an option in a portable unit.

They were. Electronic watches used them, with 32,768Hz watch crystal as
the frequency reference.

>> Other manufacturers did use centrifugal governors.
>
> So did steam engines.

Which weren't sold on the basis of their frequency accuracy or the
absence of wow and flutter.

--
Bill Sloman, Sydney

On 2024-03-05, Bill Sloman <bill.sloman@ieee.org> wrote:
> On 4/03/2024 6:45 pm, Jasen Betts wrote:
>> On 2024-02-18, Cursitor Doom <cd@notformail.com> wrote:
>>> Gentlemen,
>>>
>>> Can motor speed control ever approach the effectiveness of the old
>>> style drive belts and pulleys approach?
>>
>> you mean like a centrifugal governor?
>>
>>> Would simple PWM be enough or would there be some additional trickery
>>> needed?
>>
>> PWM could. if you sample the back EMF during the off time of the PWM and feed
>> that back to the regulator... (or read the motor speed some other way,
>> you could have an interruptor typse sensor and control speed using a
>> PLL)
>>
>> Old school when they weren't using centrifugal governors they would put
>> a compensating negative resistance in series with the motor and feed
>> the combination from a fixed DC voltage or fake that result.
>
> 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

All the old the tape recorders I pulled apart to see how they worked
used centrifugal governors (little leaf switches on the rotor),
except the one with high speed dubbing.

The Philips patent was used on record players, somehow that's not audio?
they didn't even use an op-amp just 2 transistors and used V_BE as a
voltage reference.

To me old-school is analogue speed control.

--
Jasen.
🇺🇦 Слава Україні

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.

....

kw

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.

--
Bill Sloman, Sydney

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.

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?

The permanent magnet DC motor with negative resistance driver worked
perfectly well. It was low cost, used available technology, low power,
was quiet and met the design requirements.

kw

On 7/03/2024 9:14 pm, KevinJ93 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.

Twaddle. A stepper motor is a synchronous motor, and if you are careful
how you drive it, it doesn't have any torque ripple, and it isn't any
less efficient than any other synchronous motor.

ESCAP did do a range of small stepper motors where a sine wave drive did
give a uniform rate of rotation - with others you had to massage the
waveform a bit to get uniform rotation.

> 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.

Which you could could buy in an integrated circuit. Most of mine were in
a chunk of PROM.

> 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?

Beats me.

> The permanent magnet DC motor with negative resistance driver worked
> perfectly well. It was low cost, used available technology, low power,
> was quiet and met the design requirements.

The strength of the permanent magnet depends on the it's temperature, so
the velocity feedback you get out of the motor coils does too.

It might have been "adequate" but it wasn't all that good.

--
Bill Sloman, Sydney

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?

Bill Sloman wrote:
> On 7/03/2024 9:14 pm, KevinJ93 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.
>
> Twaddle. A stepper motor is a synchronous motor, and if you are careful how
> you drive it, it doesn't have any torque ripple, and it isn't any less
> efficient than any other synchronous motor.
>
> ESCAP did do a range of small stepper motors where a sine wave drive did
> give a uniform rate of rotation - with others you had to massage the
> waveform a bit to get uniform rotation.
>
>> 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.
>
> Which you could could buy in an integrated circuit. Most of mine were in a
> chunk of PROM.
>
>> 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?
>
> Beats me.
>
>> The permanent magnet DC motor with negative resistance driver worked
>> perfectly well. It was low cost, used available technology, low power, was
>> quiet and met the design requirements.
>
> The strength of the permanent magnet depends on the it's temperature, so the
> velocity feedback you get out of the motor coils does too.
>
> It might have been "adequate" but it wasn't all that good.
>

A capstan motor sounds more could use a small AC Slosyn synchronous motor
rather than a DC Slosyn stepper. They do look quite similar and both are
made by the same vendors but they're not the same.

On Thu, 07 Mar 2024 07:26:08 -0800, John Larkin <jl@997PotHill.com>
wrote:

>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?

Prepare to be shocked!
https://www.youtube.com/watch?v=38_SVIa8BDQ

On 3/7/24 6:07 AM, Bill Sloman wrote:
> On 7/03/2024 9:14 pm, KevinJ93 wrote:
....
>>> 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.
>
> Twaddle. A stepper motor is a synchronous motor, and if you are careful
> how you drive it, it doesn't have any torque ripple, and it isn't any
> less efficient than any other synchronous motor.

Stepper motors are invariably of the reluctance type. With simple
drivers they have a great deal of cogging, which is undesirable in a
capstan drive motor.

> ESCAP did do a range of small stepper motors where a sine wave drive did
> give a uniform rate of rotation - with others you had to massage the
> waveform a bit to get uniform rotation.

Not in 1970. Even after that time they did not possess any advantage
over DC motor drive with speed stabilization based on back-emf.

Even for AC powered units where power was not an issue stepper motors
were never used. Synchronous motors with synthesized drive were
occasionally a feature but many/most used back-emf stabilization with DC
motors.

ICs were available to integrate that circuitry:

eg https://www.precisionmicrodrives.com/ab-026

>> 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.
>
> Which you could could buy in an integrated circuit. Most of mine were in
> a chunk of PROM.

Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all
your power budget.

>> 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?
>
> Beats me
>> The permanent magnet DC motor with negative resistance driver worked
>> perfectly well. It was low cost, used available technology, low power,
>> was quiet and met the design requirements.
>
> The strength of the permanent magnet depends on the it's temperature, so
> the velocity feedback you get out of the motor coils does too.
>
> It might have been "adequate" but it wasn't all that good.

There is little benefit to being more than adequate if it costs more and
will not be perceived by the customer as being better.

I'm afraid history is against you and regardless of your remonstrations
stepper motors were never used significantly or at all for capstan motors.

kw

On 3/7/24 7:26 AM, John Larkin wrote:
> On Thu, 7 Mar 2024 02:14:49 -0800, KevinJ93 <kevin_es@whitedigs.com>
....
>>>
>>
>> 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.
>

Most(all?) portable cassette players used a single motor for capstan and
take-up reel; it would definitely consume power and would probably be
the largest item in the power budget - probably only 50-100mW allowable
determined by battery life from a few C-cells or even two AA cells in
later units.

Microstepping is easy now - not so much even at the end of the cassette
tape era 30-40 years ago when CDs started to take over

>>
>> 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?

Crutchfield still has a couple of tape decks being sold. I'm sure the
market is very small.

The only reason I've used a cassette player in the last 20-30 years is
to transcribe tapes I already have into a digital format or to be able
to play things in a car that has a cassette player installed.

I wouldn't expect there is any significant new development being done.

kw

On Thu, 7 Mar 2024 12:13:59 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:

>On 3/7/24 6:07 AM, Bill Sloman wrote:
>> On 7/03/2024 9:14 pm, KevinJ93 wrote:
>...
>>>> 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.
>>
>> Twaddle. A stepper motor is a synchronous motor, and if you are careful
>> how you drive it, it doesn't have any torque ripple, and it isn't any
>> less efficient than any other synchronous motor.
>
>Stepper motors are invariably of the reluctance type. With simple
>drivers they have a great deal of cogging, which is undesirable in a
>capstan drive motor.

There are two types, PM and VR. PM steppers use bipolar coil drive and
have a strong unpowered detent. And can act as generators.

Both can microstep nicely, for smooth motion.

>
>> ESCAP did do a range of small stepper motors where a sine wave drive did
>> give a uniform rate of rotation - with others you had to massage the
>> waveform a bit to get uniform rotation.
>
>Not in 1970. Even after that time they did not possess any advantage
>over DC motor drive with speed stabilization based on back-emf.
>
>Even for AC powered units where power was not an issue stepper motors
>were never used. Synchronous motors with synthesized drive were
>occasionally a feature but many/most used back-emf stabilization with DC
>motors.

I designed a tape drive system for data storage, using the 3M tape
cartriges. The capstain driver was a stepper motor driven from 60 Hz
AC, with a cap in one leg to get a 90 degree phase shift. Motion was
very smooth.

>
>ICs were available to integrate that circuitry:
>
>eg https://www.precisionmicrodrives.com/ab-026
>
>>> 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.
>>
>> Which you could could buy in an integrated circuit. Most of mine were in
>> a chunk of PROM.
>
>Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all
>your power budget.
>
>>> 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?
>>
>> Beats me
>>> The permanent magnet DC motor with negative resistance driver worked
>>> perfectly well. It was low cost, used available technology, low power,
>>> was quiet and met the design requirements.
>>
>> The strength of the permanent magnet depends on the it's temperature, so
>> the velocity feedback you get out of the motor coils does too.
>>
>> It might have been "adequate" but it wasn't all that good.
>
>There is little benefit to being more than adequate if it costs more and
>will not be perceived by the customer as being better.
>
>I'm afraid history is against you and regardless of your remonstrations
>stepper motors were never used significantly or at all for capstan motors.

I did it.

>
>kw
>
>

On Thu, 07 Mar 2024 19:17:03 +0000, Cursitor Doom <cd@notformail.com>
wrote:

>On Thu, 07 Mar 2024 07:26:08 -0800, John Larkin <jl@997PotHill.com>
>wrote:
>
>>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?
>
>Prepare to be shocked!
>https://www.youtube.com/watch?v=38_SVIa8BDQ

It's shocking how annoying that guy is.

Tape is awful. Noisy, wobbly, hard to handle. But if you charge enough
for goofy high-end audio, some people will buy it.

On 8/03/2024 7:13 am, KevinJ93 wrote:
> On 3/7/24 6:07 AM, Bill Sloman wrote:
>> On 7/03/2024 9:14 pm, KevinJ93 wrote:
> ...
>>>> 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.
>>
>> Twaddle. A stepper motor is a synchronous motor, and if you are
>> careful how you drive it, it doesn't have any torque ripple, and it
>> isn't any less efficient than any other synchronous motor.
>
> Stepper motors are invariably of the reluctance type. With simple
> drivers they have a great deal of cogging, which is undesirable in a
> capstan drive motor.
>
>> ESCAP did do a range of small stepper motors where a sine wave drive
>> did give a uniform rate of rotation - with others you had to massage
>> the waveform a bit to get uniform rotation.
>
> Not in 1970. Even after that time they did not possess any advantage
> over DC motor drive with speed stabilization based on back-emf.

Don't be silly. Back-emf depends on the strenght of the magnetic field
generating the basck-emf, and that is temperature dependent.

Synchronous motors rotate at a rate that reflects the stability of the
frequency source that determines the drive frequency, and reasonably
stable frequency source - watch crystals have been around for ages.
>
> Even for AC powered units where power was not an issue stepper motors
> were never used. Synchronous motors with synthesized drive were
> occasionally a feature but many/most used back-emf stabilization with DC
> motors.
>
> ICs were available to integrate that circuitry:
>
> eg https://www.precisionmicrodrives.com/ab-026
>
>>> 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.
>>
>> Which you could could buy in an integrated circuit. Most of mine were
>> in a chunk of PROM.
>
> Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all
> your power budget.

It didn't - and it wasn't bipolar.

>>> 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?
>>
>> Beats me
> >
>>> The permanent magnet DC motor with negative resistance driver worked
>>> perfectly well. It was low cost, used available technology, low
>>> power, was quiet and met the design requirements.
>>
>> The strength of the permanent magnet depends on the it's temperature,
>> so the velocity feedback you get out of the motor coils does too.
>>
>> It might have been "adequate" but it wasn't all that good.
>
> There is little benefit to being more than adequate if it costs more and
> will not be perceived by the customer as being better.

Tape recorder that didn't play back the recorded frequency weren't
perceived to be "good" by their customers. That didn't worry the bottom
end of the market.

> I'm afraid history is against you and regardless of your remonstrations
> stepper motors were never used significantly or at all for capstan motors.

History doesn't make a cheap and nasty solution anything other than
cheap and nasty. The thread is about what Cursitor Doom should do to get
his antique tape recorder working again, and getting hold of the
original motors used to drive it doesn't seem to be an option.

--
Bill Sloman, Sydney

On 3/7/24 7:18 PM, John Larkin wrote:
> On Thu, 7 Mar 2024 12:13:59 -0800, KevinJ93 <kevin_es@whitedigs.com>
> wrote:
>
....
>>
>> Stepper motors are invariably of the reluctance type. With simple
>> drivers they have a great deal of cogging, which is undesirable in a
>> capstan drive motor.
>
> There are two types, PM and VR. PM steppers use bipolar coil drive and
> have a strong unpowered detent. And can act as generators.

Yes, I was wrong.

> Both can microstep nicely, for smooth motion.
>

Given appropriate driving circuitry that would have been expensive and
power consuming in 1970.

>
>>
>>> ESCAP did do a range of small stepper motors where a sine wave drive did
>>> give a uniform rate of rotation - with others you had to massage the
>>> waveform a bit to get uniform rotation.
>>
....

kw

On 3/7/24 8:48 PM, Bill Sloman wrote:
> On 8/03/2024 7:13 am, KevinJ93 wrote:
....
>>
>> Not in 1970. Even after that time they did not possess any advantage
>> over DC motor drive with speed stabilization based on back-emf.
>
> Don't be silly. Back-emf depends on the strenght of the magnetic field
> generating the basck-emf, and that is temperature dependent.

At about 0.2% per deg the magnetic field strength stability was adequate
for the speed accuracy required under the required environmental conditions.

>
> Synchronous motors rotate at a rate that reflects the stability of the
> frequency source that determines the drive frequency, and reasonably
> stable frequency source - watch crystals have been around for ages.

>> Even for AC powered units where power was not an issue stepper motors
>> were never used. Synchronous motors with synthesized drive were
>> occasionally a feature but many/most used back-emf stabilization with
>> DC motors.
>>
>> ICs were available to integrate that circuitry:
>>
>> eg https://www.precisionmicrodrives.com/ab-026
>>
>>>> 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.
>>>
>>> Which you could could buy in an integrated circuit. Most of mine were
>>> in a chunk of PROM.
>>
>> Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all
>> your power budget.
>
> It didn't - and it wasn't bipolar.

MOS EPROMS such as the 1702 were cumbersome to use with multiple
supplies required. The logic to drive them would have been TTL consuming
significant amounts of power as well as expensive.

The first EPROMS that were easy to use, such as the 2708 weren't widely
available till the late 70's.

>>>> 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?
>>>
>>> Beats me
> > >
>>>> The permanent magnet DC motor with negative resistance driver worked
>>>> perfectly well. It was low cost, used available technology, low
>>>> power, was quiet and met the design requirements.
>>>
>>> The strength of the permanent magnet depends on the it's temperature,
>>> so the velocity feedback you get out of the motor coils does too.
>>>
>>> It might have been "adequate" but it wasn't all that good.
>>
>> There is little benefit to being more than adequate if it costs more
>> and will not be perceived by the customer as being better.
>
> Tape recorder that didn't play back the recorded frequency weren't
> perceived to be "good" by their customers. That didn't worry the bottom
> end of the market.

Few customers had perfect pitch, an error of 1% was much preferable to
high cost.

You may call them 'cheap and nasty' but the major portion of the market
found this solution acceptable, only the high end went for more exotic
approaches.

Wow and flutter performance was much more important and using a DC motor
and belt drive with small capstans and a flywheel gave acceptable
performance.

I see that tape decks available at Crutchfield currently have a pitch
control so the speed can be varied anyway.

>> I'm afraid history is against you and regardless of your
>> remonstrations stepper motors were never used significantly or at all
>> for capstan motors.
>
> History doesn't make a cheap and nasty solution anything other than
> cheap and nasty. The thread is about what Cursitor Doom should do to get
> his antique tape recorder working again, and getting hold of the
> original motors used to drive it doesn't seem to be an option.
>

kw

On Fri, 8 Mar 2024 10:30:08 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:

>On 3/7/24 7:18 PM, John Larkin wrote:
>> On Thu, 7 Mar 2024 12:13:59 -0800, KevinJ93 <kevin_es@whitedigs.com>
>> wrote:
>>
>...
>>>
>>> Stepper motors are invariably of the reluctance type. With simple
>>> drivers they have a great deal of cogging, which is undesirable in a
>>> capstan drive motor.
>>
>> There are two types, PM and VR. PM steppers use bipolar coil drive and
>> have a strong unpowered detent. And can act as generators.
>
>Yes, I was wrong.
>
>> Both can microstep nicely, for smooth motion.
>>
>
>Given appropriate driving circuitry that would have been expensive and
>power consuming in 1970.

My phase-shifted 60 Hz tape drive thing worked pretty well, for the
time. I used a few triacs to get stop/fwd/reverse. One phase of the
stepper was raw 60 Hz from a transformer, and the other phase had a
series R+C to get a 90 degree phase shift. We tweaked the RC to get
the smoothest rotation.

I've done a fair number of stepper drivers, like the ones to tune the
superconductive cavities at CEBAF, but I've never driven, or seen, a
VR type.

Aerospace people like to use "torque motors", which are basically big
VR steppers.

On 9/03/2024 5:30 am, KevinJ93 wrote:
> On 3/7/24 7:18 PM, John Larkin wrote:
>> On Thu, 7 Mar 2024 12:13:59 -0800, KevinJ93 <kevin_es@whitedigs.com>
>> wrote:
>>
> ...
>>>
>>> Stepper motors are invariably of the reluctance type. With simple
>>> drivers they have a great deal of cogging, which is undesirable in a
>>> capstan drive motor.
>>
>> There are two types, PM and VR. PM steppers use bipolar coil drive and
>> have a strong unpowered detent. And can act as generators.
>
> Yes, I was wrong.
>
>> Both can microstep nicely, for smooth motion.
>
> Given appropriate driving circuitry that would have been expensive and
> power consuming in 1970.

Nonsense. The cheap way of making an approximation to a sine wave is
pulse width modulation.

https://www.tinaja.com/glib/sinquest.pdf

That document is from 1997, but the idea has been around for a lot
longer. I used it in 1975 - if not to make sine waves - and it is cheap
and efficient. The "modified square wave" - which has no third harmonic
content - is equally old.

<snip>

--
Bill Sloman, Sydney

On 9/03/2024 5:49 am, KevinJ93 wrote:
> On 3/7/24 8:48 PM, Bill Sloman wrote:
>> On 8/03/2024 7:13 am, KevinJ93 wrote:
> ...
>>>
>>> Not in 1970. Even after that time they did not possess any advantage
>>> over DC motor drive with speed stabilization based on back-emf.
>>
>> Don't be silly. Back-emf depends on the strenght of the magnetic field
>> generating the basck-emf, and that is temperature dependent.
>
> At about 0.2% per deg the magnetic field strength stability was adequate
> for the speed accuracy required under the required environmental
> conditions.

Motors run hotter than their environment

>> Synchronous motors rotate at a rate that reflects the stability of the
>> frequency source that determines the drive frequency, and reasonably
>> stable frequency source - watch crystals have been around for ages.
>
>>> Even for AC powered units where power was not an issue stepper motors
>>> were never used. Synchronous motors with synthesized drive were
>>> occasionally a feature but many/most used back-emf stabilization with
>>> DC motors.
>>>
>>> ICs were available to integrate that circuitry:
>>>
>>> eg https://www.precisionmicrodrives.com/ab-026
>>>
>>>>> 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.
>>>>
>>>> Which you could could buy in an integrated circuit. Most of mine
>>>> were in a chunk of PROM.
>>>
>>> Not in 1970. Even by the late 70's a bipolar (P)ROM would use up all
>>> your power budget.
>>
>> It didn't - and it wasn't bipolar.
>
> MOS EPROMS such as the 1702 were cumbersome to use with multiple
> supplies required.

It was one-time programmable, not an EPROM.

>The logic to drive them would have been TTL consuming
> significant amounts of power as well as expensive.

CMOS was around and cheap. I'd first used it around 1975, and the price
fell by a factor of three as I was developing the 1975 circuit.

> The first EPROMS that were easy to use, such as the 2708 weren't widely
> available till the late 70's.

The stepper motor circuit that I worked on was developed in 1978.

<snip>

--
Bill Sloman, Sydney

On Thu, 07 Mar 2024 19:18:51 -0800, John Larkin <jl@997PotHill.com>
wrote:

>On Thu, 7 Mar 2024 12:13:59 -0800, KevinJ93 <kevin_es@whitedigs.com>
>wrote:
>
>>On 3/7/24 6:07 AM, Bill Sloman wrote:
>>> On 7/03/2024 9:14 pm, KevinJ93 wrote:
>>...
>>>>> 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.
>>>
>>> Twaddle. A stepper motor is a synchronous motor, and if you are careful
>>> how you drive it, it doesn't have any torque ripple, and it isn't any
>>> less efficient than any other synchronous motor.
>>
>>Stepper motors are invariably of the reluctance type. With simple
>>drivers they have a great deal of cogging, which is undesirable in a
>>capstan drive motor.
>
>There are two types, PM and VR. PM steppers use bipolar coil drive and
>have a strong unpowered detent. And can act as generators.
>
>Both can microstep nicely, for smooth motion.
>

Could a VR stepper be used as a generator? I think so.