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.
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?
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:[snip]
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.
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?
And what is it that controls the speed of the tape - the
capstan/pinch-wheel motor or the relevant reel motor?
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?
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:[snip]
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.
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.
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 Monday, February 19, 2024 at 5:52:19 AM UTC+11, Cursitor Doom wrote: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.
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
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.
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>
On 2024-02-19 01:44, Anthony William Sloman wrote: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.
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
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.
A BLDC motor with tach could make a very
nice capstain drive, with a lot of electronics.
On Mon, 19 Feb 2024 13:21:18 +0100, "Carlos E.R."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.
<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
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.
On Mon, 19 Feb 2024 13:35:58 +0000, Cursitor Doom <cd@notformail.com>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.
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
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 Mon, 19 Feb 2024 09:10:13 -0800, John Larkin <jl@997PotHill.com>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.
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
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.
On Mon, 19 Feb 2024 09:10:13 -0800, John Larkin <jl@997PotHill.com>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.
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
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
mandag den 19. februar 2024 kl. 18.11.59 UTC+1 skrev John Larkin: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.
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
If there's a belt, that will further lowpass filter angular vibration.
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.
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
On Mon, 19 Feb 2024 15:31:47 -0800 (PST), Lasse Langwadt Christensen ><langwadt@fonz.dk> wrote: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.
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
If there's a belt, that will further lowpass filter angular vibration.
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.
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
Most any stepper motor can be microstepped, and make smooth quiet
motion. Drive the windings with sine/cosine waves instead of brutal
steps. You can do that in uP code: software DDS and a sin/cos lookup
table, into a couple of PWM blocks.
I did that ages ago with a 68332, with maybe 1% of the compute power
of a Raspberry Pi Pico.
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry
about.
On Tue, 20 Feb 2024 12:27:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry >>about.
When the machine is in "play" or "record" mode, I mean; not during FF
or rewind.
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected?
Cursitor Doom <cd@notformail.com> writes:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected?
The speed of the tape depends not only on the spool RPM but also how
much tape is present, since that changes the effective diameter. If the >spools have different amounts of tape on them (normal) they'll have to
move at different RPMs to have the same linear tape speed.
tirsdag den 20. februar 2024 kl. 01.15.30 UTC+1 skrev John Larkin: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.
On Mon, 19 Feb 2024 15:31:47 -0800 (PST), Lasse Langwadt Christensen
<lang...@fonz.dk> wrote:
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
Most any stepper motor can be microstepped, and make smooth quietIf there's a belt, that will further lowpass filter angular vibration.
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.
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
motion. Drive the windings with sine/cosine waves instead of brutal
steps. You can do that in uP code: software DDS and a sin/cos lookup
table, into a couple of PWM blocks.
sure, and almost all steppers are now driven like that and there a plenty of >cheap integrated IC that does it all, but unless you run very slow they still make noise
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.
Cursitor Doom <cd@notformail.com> writes:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected?
The speed of the tape depends not only on the spool RPM but also how
much tape is present, since that changes the effective diameter. If the >spools have different amounts of tape on them (normal) they'll have to
move at different RPMs to have the same linear tape speed.
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry
about.
The speed of the tape depends not only on the spool RPM but also how
much tape is present, since that changes the effective diameter. If the >>spools have different amounts of tape on them (normal) they'll have to
move at different RPMs to have the same linear tape speed.
If I understand this correctly, one doesn't need to worry about that
aspect, because it will 'just happen automatically' on play and
record.
The capstain determines the tape speed. The takeup reel motor just
applies a gentle torque and the feed reel motor a bit of drag. The
reel speeds are controlled by the tape speed, namely the capstain.
The tape drives fed the tape into a deep trough on one side of the
reader before it went into the reading head, and had a second trough
on the other side to take up the tape after it had been read. Air was
pumped into both troughs to keep two fairly long loops under minimal
tension. If you were operating the machine at four in the morning
there wasn't a lot other stuff going on to attract your attention.
On Tue, 20 Feb 2024 12:27:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry >about.
I don't recall any decks that changed the reel motor drives at
different capstain speeds. Certainly none that were aware of the
amount of tape on each reel.
The usual BLDC doesn't speed regulate. Speed depends on the DC supply
voltage and the loading. Basically, it tries as hard as it can.
The usual BLDC doesn't speed regulate. Speed depends on the DC supply >>voltage and the loading. Basically, it tries as hard as it can.
That's correct. But some speed controllers also support a constant
speed mode,
John Larkin <jl@997PotHill.com> wrote:
On Tue, 20 Feb 2024 12:27:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry
about.
I don't recall any decks that changed the reel motor drives at
different capstain speeds. Certainly none that were aware of the
amount of tape on each reel.
I have a vague recollection that there was a machine that boosted the
takeup motor temporarily at high tape speeds to reduce 'billowing'
during startup -- but I can't remember which machine it was (EMI BTR2 or >Marconi-Stille ??). The Ferrograph Series 7 had two torque settings to
deal with small and large-hub reels - but it didn't seem to make much >difference.
The Collaro 'pushmi-pullyu' deck had a constant speed spool motor with >variable friction drive to the spool hubs controlled by tension arms.
The spool motor and the capstan motors were identical (apart from
diection of rotations) and swapped functions when the deck went into
reverse.
Grundig 'Stenorette' dictating machines had a constant rotational speed
spool permanently built into the machine, and no capstan. The tape
cassette had a loose end hanging out with a loop which you hooked around
a pillar on the drive spool and the tape gradually sped up as it built
up on the spool hub. As the recordings had also been made on the same
type of machine, the pitch didn't vary on playback.
Wire recorders almost all used spool drive, but there was one which used
a capstan with the wire wrapped around it in a single turn with no
pressure roller.
On Tue, 20 Feb 2024 15:55:42 -0500, DJ Delorie <dj@delorie.com> wrote:
Robert Roland <fake@ddress.no> writes:
The usual BLDC doesn't speed regulate. Speed depends on the DC supply >>>>voltage and the loading. Basically, it tries as hard as it can.
That's correct. But some speed controllers also support a constant
speed mode,
And when you get to industrial BLDC motors, you add smarter controllers
and position feedback, and you can control pretty much anything wrt that >>motor - speed, torque, position, acceleration, etc. Yup, model
helicopters and big CNC machines use the same type of motors :-)
Small fan-type BLDC motors often have 4 pins: V+, ground, PWM in, and
tach out. The PWM input controls speed, not very accurately, from zero
to max.
Robert Roland <fake@ddress.no> writes:
The usual BLDC doesn't speed regulate. Speed depends on the DC supply >>>voltage and the loading. Basically, it tries as hard as it can.
That's correct. But some speed controllers also support a constant
speed mode,
And when you get to industrial BLDC motors, you add smarter controllers
and position feedback, and you can control pretty much anything wrt that >motor - speed, torque, position, acceleration, etc. Yup, model
helicopters and big CNC machines use the same type of motors :-)
On Tue, 20 Feb 2024 14:53:00 -0800, john larkin <jl@650pot.com> wrote:
On Tue, 20 Feb 2024 15:55:42 -0500, DJ Delorie <dj@delorie.com> wrote:
Robert Roland <fake@ddress.no> writes:
The usual BLDC doesn't speed regulate. Speed depends on the DC supply >>>>>voltage and the loading. Basically, it tries as hard as it can.
That's correct. But some speed controllers also support a constant
speed mode,
And when you get to industrial BLDC motors, you add smarter controllers >>>and position feedback, and you can control pretty much anything wrt that >>>motor - speed, torque, position, acceleration, etc. Yup, model >>>helicopters and big CNC machines use the same type of motors :-)
Small fan-type BLDC motors often have 4 pins: V+, ground, PWM in, and
tach out. The PWM input controls speed, not very accurately, from zero
to max.
Hence the need for feedback. I wonder if there's a motor that can spin
at a given speed accurately without f/back?
Small fan-type BLDC motors often have 4 pins: V+, ground, PWM in, and
tach out. The PWM input controls speed, not very accurately, from zero
to max.
Hence the need for feedback. I wonder if there's a motor that can spin
at a given speed accurately without f/back?
On Tue, 20 Feb 2024 12:27:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Can I just get some clarification on one point here. The two spools
are not speed controlled as such and just spin or drag (as the case
may be) at the same speed regardless of the tape speed selected? So
it's only the capstan motor that needs precise control speed? That
seems to be implication of what's been posted here so far and it would
make things much simpler if there was only one motor's speed to worry >>about.
I don't recall any decks that changed the reel motor drives at
different capstain speeds. Certainly none that were aware of the
amount of tape on each reel.
Big sci-fi movie type computer tape drives used air columns to buffer
the reels. That reduced the effective inertia of the reels to about
zero. The capstains could start/stop every record, ballpark an inch of
tape, as needed.
I designed a tape controller, Ampex 9-track to PDP-11. I'd forgotten
all about that until this thread.
Hence the need for feedback. I wonder if there's a motor that can spin
at a given speed accurately without f/back?
On Tue, 20 Feb 2024 23:09:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Hence the need for feedback. I wonder if there's a motor that can spin
at a given speed accurately without f/back?
That would be called a synchronous motor. A BLDC motor is actually a >synchronous motor. If it gets blindly commutated at a certain speed,
it will rotate at that speed (but it will be inefficient). It is
possible to abuse a BLDC motor as a stepper motor. If you apply
current to one of its windings, the rotor will snap into one position
and hold that position.
In order to optimize efficiency, the controller needs to know when to >commutate. Hobby controllers are available in two types, sensorless
and sensored. Sensorless systems need almost no additional hardware
for the feedback. They simply measure the EMF produced by the rotating >magnets.
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
On Tue, 20 Feb 2024 23:09:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Hence the need for feedback. I wonder if there's a motor that can spin
at a given speed accurately without f/back?
That would be called a synchronous motor. A BLDC motor is actually a
synchronous motor. If it gets blindly commutated at a certain speed,
it will rotate at that speed (but it will be inefficient). It is
possible to abuse a BLDC motor as a stepper motor. If you apply
current to one of its windings, the rotor will snap into one position
and hold that position.
In order to optimize efficiency, the controller needs to know when to
commutate. Hobby controllers are available in two types, sensorless
and sensored. Sensorless systems need almost no additional hardware
for the feedback. They simply measure the EMF produced by the rotating
magnets.
Thanks. I'm just trying to work out which type would be most suited to
the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
On 22/02/2024 11:40 am, Cursitor Doom wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
On Tue, 20 Feb 2024 23:09:10 +0000, Cursitor Doom <cd@notformail.com>
wrote:
Hence the need for feedback. I wonder if there's a motor that can spin >>>> at a given speed accurately without f/back?
That would be called a synchronous motor. A BLDC motor is actually a
synchronous motor. If it gets blindly commutated at a certain speed,
it will rotate at that speed (but it will be inefficient). It is
possible to abuse a BLDC motor as a stepper motor. If you apply
current to one of its windings, the rotor will snap into one position
and hold that position.
In order to optimize efficiency, the controller needs to know when to
commutate. Hobby controllers are available in two types, sensorless
and sensored. Sensorless systems need almost no additional hardware
for the feedback. They simply measure the EMF produced by the rotating
magnets.
Thanks. I'm just trying to work out which type would be most suited to
the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
The obvious answer is a stepper motor (synchronous motor) with a >crystal-controlled frequency drive.
It will work better if the controller can generate acceleration and >deceleration sequences to make slow and smooth changes in rotational
speed - the spools of tape have rotational intertia and you can't change >their speed of rotation all that quickly.
Once you have got it up to speed, the rotational frequency will be as
stable as your crystal clock. There will some phase lag between the
drive waveform and the position of the rotor - it creates the torque
that counteracts the friction losses, but that should be pretty stable.
You do need some kind of stall detector to accelerate the motor up to
speed again after some ham-fisted user has stopped it's rotation.
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to
the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to
the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
The most important difference between the two systems, is starting
torque.
Since the sensorless systems use the moving magnets to determine
commutation timing, the motor must be spinning in order to commutate.
Of course, it needs commutation in order to spin, so you essentially
have a catch-22 situation.
There are different strategies to overcome the startup problem. The
simplest one is to simply commutate "blindly" at low current and see
if any timing signals show up. There are more sophisticated methods,
but common to them all is that they provide very low torque at zero
speed. For propellers or helicopter rotors, this is not a problem, so sensorless systems are used. For cars, however, starting torque is
important, so sensored systems are used.
The sensors are simply a few Hall effect sensors. There is no need for
any shaft encoders. In hobby products, the sensors are built in to the
motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to
the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
The most important difference between the two systems, is starting
torque.
Since the sensorless systems use the moving magnets to determine
commutation timing, the motor must be spinning in order to commutate.
Of course, it needs commutation in order to spin, so you essentially
have a catch-22 situation.
There are different strategies to overcome the startup problem. The
simplest one is to simply commutate "blindly" at low current and see
if any timing signals show up. There are more sophisticated methods,
but common to them all is that they provide very low torque at zero
speed. For propellers or helicopter rotors, this is not a problem, so
sensorless systems are used. For cars, however, starting torque is
important, so sensored systems are used.
Stepper motors always provide the same torque when they step slowly at
any speed - as long as the current through coil can get up to the
tolerable peak, you will get the same torque.
If the magnetic field lines up with position of the rotor, you won't get
any torque, so the strategy is to start by stepping the magnetic field
slowly enough that rotor can follow the rotating magnetic field, which
gets rid of any initial stiction. At low step rates the rotor can
oscillate around the zero torque position, and you have to avoid steps
rates that match that oscillation frequency. Once you have got the rotor >moving slowly, you know where it is and you can start your acceleration >sequence.
The sensors are simply a few Hall effect sensors. There is no need for
any shaft encoders. In hobby products, the sensors are built in to the
motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft,
and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users
will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we
need to treat him as if he could acquire some sophistication.
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to >>>> the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
The most important difference between the two systems, is starting
torque.
Since the sensorless systems use the moving magnets to determine
commutation timing, the motor must be spinning in order to commutate.
Of course, it needs commutation in order to spin, so you essentially
have a catch-22 situation.
There are different strategies to overcome the startup problem. The
simplest one is to simply commutate "blindly" at low current and see
if any timing signals show up. There are more sophisticated methods,
but common to them all is that they provide very low torque at zero
speed. For propellers or helicopter rotors, this is not a problem, so
sensorless systems are used. For cars, however, starting torque is
important, so sensored systems are used.
Stepper motors always provide the same torque when they step slowly at
any speed - as long as the current through coil can get up to the
tolerable peak, you will get the same torque.
If the magnetic field lines up with position of the rotor, you won't get >>any torque, so the strategy is to start by stepping the magnetic field >>slowly enough that rotor can follow the rotating magnetic field, which
gets rid of any initial stiction. At low step rates the rotor can
oscillate around the zero torque position, and you have to avoid steps >>rates that match that oscillation frequency. Once you have got the rotor >>moving slowly, you know where it is and you can start your acceleration >>sequence.
The sensors are simply a few Hall effect sensors. There is no need for
any shaft encoders. In hobby products, the sensors are built in to the
motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft,
and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users >>will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we
need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
On Sun, 25 Feb 2024 17:46:41 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com>
wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no>
wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to >>>>> the role of a capstan roller motor to use at 3 fixed speeds (after
gearing down if necessary).
The most important difference between the two systems, is starting
torque.
Since the sensorless systems use the moving magnets to determine
commutation timing, the motor must be spinning in order to commutate.
Of course, it needs commutation in order to spin, so you essentially
have a catch-22 situation.
There are different strategies to overcome the startup problem. The
simplest one is to simply commutate "blindly" at low current and see
if any timing signals show up. There are more sophisticated methods,
but common to them all is that they provide very low torque at zero
speed. For propellers or helicopter rotors, this is not a problem, so
sensorless systems are used. For cars, however, starting torque is
important, so sensored systems are used.
Stepper motors always provide the same torque when they step slowly at >>>any speed - as long as the current through coil can get up to the >>>tolerable peak, you will get the same torque.
If the magnetic field lines up with position of the rotor, you won't get >>>any torque, so the strategy is to start by stepping the magnetic field >>>slowly enough that rotor can follow the rotating magnetic field, which >>>gets rid of any initial stiction. At low step rates the rotor can >>>oscillate around the zero torque position, and you have to avoid steps >>>rates that match that oscillation frequency. Once you have got the rotor >>>moving slowly, you know where it is and you can start your acceleration >>>sequence.
The sensors are simply a few Hall effect sensors. There is no need for >>>> any shaft encoders. In hobby products, the sensors are built in to the >>>> motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft, >>>and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users >>>will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we >>>need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
Sloman's real enemy is Sloman.
On Sun, 25 Feb 2024 10:13:45 -0800, John Larkin <jl@997PotHill.com>
wrote:
On Sun, 25 Feb 2024 17:46:41 +0000, Cursitor Doom <cd@notformail.com> >>wrote:
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com> >>>>> wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no> >>>>>> wrote:
Hobby controllers are available in two types, sensorless
and sensored.
Thanks. I'm just trying to work out which type would be most suited to >>>>>> the role of a capstan roller motor to use at 3 fixed speeds (after >>>>>> gearing down if necessary).
The most important difference between the two systems, is starting
torque.
Since the sensorless systems use the moving magnets to determine
commutation timing, the motor must be spinning in order to commutate. >>>>> Of course, it needs commutation in order to spin, so you essentially >>>>> have a catch-22 situation.
There are different strategies to overcome the startup problem. The
simplest one is to simply commutate "blindly" at low current and see >>>>> if any timing signals show up. There are more sophisticated methods, >>>>> but common to them all is that they provide very low torque at zero
speed. For propellers or helicopter rotors, this is not a problem, so >>>>> sensorless systems are used. For cars, however, starting torque is
important, so sensored systems are used.
Stepper motors always provide the same torque when they step slowly at >>>>any speed - as long as the current through coil can get up to the >>>>tolerable peak, you will get the same torque.
If the magnetic field lines up with position of the rotor, you won't get >>>>any torque, so the strategy is to start by stepping the magnetic field >>>>slowly enough that rotor can follow the rotating magnetic field, which >>>>gets rid of any initial stiction. At low step rates the rotor can >>>>oscillate around the zero torque position, and you have to avoid steps >>>>rates that match that oscillation frequency. Once you have got the rotor >>>>moving slowly, you know where it is and you can start your acceleration >>>>sequence.
The sensors are simply a few Hall effect sensors. There is no need for >>>>> any shaft encoders. In hobby products, the sensors are built in to the >>>>> motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft, >>>>and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users >>>>will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we >>>>need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being >>>more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
Sloman's real enemy is Sloman.
His only supporter here was 3rdWit, who it transpired was just a
sock-puppet. I'm afraid Bill's become something of a sad and rather
tragic figure here in recent years.
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no> wrote:
The sensors are simply a few Hall effect sensors. There is no need for
any shaft encoders. In hobby products, the sensors are built in to the
motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft,
and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users
will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we
need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
On Sun, 25 Feb 2024 10:13:45 -0800, John Larkin <jl@997PotHill.com> wrote:
On Sun, 25 Feb 2024 17:46:41 +0000, Cursitor Doom <cd@notformail.com> wrote: >>> On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no> wrote:
Cursitor Doom isn't a sophisticated user, but if he is posting here we >>>> need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
Sloman's real enemy is Sloman.
His only supporter here was 3rdWit, who it transpired was just a
sock-puppet.
I'm afraid Bill's become something of a sad and rather tragic figure here in recent years.
On Sun, 25 Feb 2024 17:46:41 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no> wrote:
The sensors are simply a few Hall effect sensors. There is no need for >>>> any shaft encoders. In hobby products, the sensors are built in to the >>>> motor at the factory, so the end user simply sees a few extra wires
that need to be connected to the controller.
The Hall sensors are shaft encoders - the rotor is bonded to the shaft,
and magnets in the rotor are what you are detecting.
The end user may see them as a few extra wires, but sophisticated users
will see them for what they are.
Cursitor Doom isn't a sophisticated user, but if he is posting here we
need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
Sloman's real enemy is Sloman.
On Sun, 25 Feb 2024 18:52:41 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Sun, 25 Feb 2024 10:13:45 -0800, John Larkin <jl@997PotHill.com wrote
On Sun, 25 Feb 2024 17:46:41 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 26 Feb 2024 01:57:01 +1100, Bill Sloman <bill.sloman@ieee.org> wrote:
On 26/02/2024 12:34 am, Robert Roland wrote:
On Thu, 22 Feb 2024 00:40:01 +0000, Cursitor Doom <cd@notformail.com> wrote:
On Wed, 21 Feb 2024 14:52:19 +0100, Robert Roland <fake@ddress.no> wrote:
Cursitor Doom isn't a sophisticated user, but if he is posting here we >>>>> need to treat him as if he could acquire some sophistication.
Up until that last paragraph I was just about to commend you on being
more like the old Bill Sloman who posted helpful advice here back in
the day. You just can't resist throwing barbs, can you? Sigh...
Sloman's real enemy is Sloman.
His only supporter here was 3rdWit, who it transpired was just a
sock-puppet.
I'm afraid Bill's become something of a sad and rather
tragic figure here in recent years.
Neither supporters nor enemies make sense in an electronic design
forum. This ain't social media.
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?
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.
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.
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.
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
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.
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 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.
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
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.
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.
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.
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.
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.
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?
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.
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?
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.
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.
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.
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?
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:...
Obviously Philips didn't agree with you. For a consumer product used >>>>> over a benign temperature range it was fine.
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. >>>>>
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 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.
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.
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.
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.
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 hasBeats me
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.
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.
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.
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.
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 moreWhich you could could buy in an integrated circuit. Most of mine
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. >>>>
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.
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.
On 3/8/24 8:42 PM, Bill Sloman wrote:
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
With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the >temperature differential was small.
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.
If it was NMOS it was almost certainly an EPROM in a cheaper package
without the quartz window.
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>
On 3/8/24 8:42 PM, Bill Sloman wrote:
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
With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the temperature differential was small.
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.
If it was NMOS it was almost certainly an EPROM in a cheaper package
without the quartz window.
On Sat, 9 Mar 2024 14:56:43 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:
On 3/8/24 8:42 PM, Bill Sloman wrote:
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
With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the >>temperature differential was small.
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.
If it was NMOS it was almost certainly an EPROM in a cheaper package >>without the quartz window.
1702 was a p-mos UV-erase part. It was called an eprom.
On Sat, 09 Mar 2024 15:13:20 -0800, John Larkin <jl@997PotHill.com>
wrote:
On Sat, 9 Mar 2024 14:56:43 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:
On 3/8/24 8:42 PM, Bill Sloman wrote:
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
With only 50-100mW being consumed by the motor (10's of mA at 3-6V) the >>>temperature differential was small.
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.
If it was NMOS it was almost certainly an EPROM in a cheaper package >>>without the quartz window.
1702 was a p-mos UV-erase part. It was called an eprom.
Are EPROMs obsolete now? I assume they must be or we wouldn't have USB
drives and SD cards etc.
On Sat, 09 Mar 2024 15:13:20 -0800, John Larkin <jl@997PotHill.com>
wrote:
On Sat, 9 Mar 2024 14:56:43 -0800, KevinJ93 <kevin_es@whitedigs.com>
wrote:
On 3/8/24 8:42 PM, Bill Sloman wrote:
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:
1702 was a p-mos UV-erase part. It was called an eprom.
Are EPROMs obsolete now? I assume they must be or we wouldn't have USB
drives and SD cards etc.
On Sat, 9 Mar 2024 14:56:43 -0800, KevinJ93 <kevin_es@whitedigs.com>...
wrote:
On 3/8/24 8:42 PM, Bill Sloman wrote:
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.
If it was NMOS it was almost certainly an EPROM in a cheaper package
without the quartz window.
1702 was a p-mos UV-erase part. It was called an eprom.
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