Why are capstan wheels different size?

[MJC]

In article <c132015e-fe0f-4a70-be7a-d5bdeb18c48f@googlegroups.com>,
pallison49@gmail.com says...

MJC wrote:


And I have long thought that with the small diameter of the capstan it
must be the availability of excellent, and cheap, bearings for the shaft
that made it possible to keep the wow and flutter down to acceptable
levels...


** The vast majority use plain bearings and rely on a flywheel to do the rest.



.... Phil

Sure, but my point was that any chatter in the bearings is just as bad
as rotational variation and is not damped by the flywheel. So the plain
bearings have to be accurate and long-lasting.

Mike.

 

[Adrian Caspersz]

On 12/03/16 12:31, jurb6006@gmail.com wrote:

"I did initially think closed loop but then capstans would be
revolving in opposite directions? It would be an extreme way to
apply tension >to a tape. "

Do you understand mechanics at all ? It helps.

Those things are

turning in OPPOSITE directions and therefore that deck is NOT a true
dual capstan.

Sorry, you can see I goofed up my sentence. Should have written

"I did initially think closed loop but then capstans ARE
revolving in opposite directions? (So not)"

It has two but the other one is used to regulate tapes

speed in reverse. That is all.

It does not have the the qualitative edge over a single capstan deck
at all, that part of the mechanism simply facilitates the reverse
function. It is not dual capstan at all. To me, and anyone who knows
tape, dual capstan means they both work at the same time, and in that
the deck, THEY DO NOT. It is either one or the other, depending on if
it it is in the forward or reverse mode. At no time are both pinch
rollers engaged. Only one at a time.

When it's running look and see, and you will see.

Agreed.

--
Adrian C

 

[MJC]

In article <83973214-241c-42fc-a32f-fbcd10ea0572@googlegroups.com>,
pallison49@gmail.com says...

MJC wrote:


And I have long thought that with the small diameter of the capstan it
must be the availability of excellent, and cheap, bearings for the shaft
that made it possible to keep the wow and flutter down to acceptable
levels...


** The vast majority use plain bearings and rely on a flywheel to
do the rest.




Sure, but my point was that any chatter in the bearings is just as bad
as rotational variation and is not damped by the flywheel. So the plain
bearings have to be accurate and long-lasting.


** You have completely forgotten the damping effect of side-ways pressure from the pinch roller.



.... Phil

I certainly was not taking it into account. Probably because it is
movement along the length of the tape and not sideways that gives rise
to speed modulation at the pick-up.

Mike.

 

[DaveC]

jurb6006@gmail.com wrote:

> Those things are turning in OPPOSITE directions

Yikes! You’re right...

(op)

 

[DaveC]

pfjw@aol.com wrote:

The capstan is a passive device. The motor pulley diameter via the *pinch
roller* determines the tape speed. The capstan wheel can be any size at all.

By my mind that is backward: the pinch roller is passive (not being driven).
The capstan shaft (~2mm diam) is driven by capstan flywheel/belt/motor
pulley.

No?

Thanks.

(op)

 

[N_Cook]

On 11/03/2016 21:22, DaveC wrote:

Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...

Aiwa AD WX888 , 1997,I worked on once, spindle to one capstan 2.49mm
diameter and the other 2.69mm

 

[legg]

On Sat, 12 Mar 2016 17:37:50 +0000, N_Cook <diverse@tcp.co.uk> wrote:

On 11/03/2016 21:22, DaveC wrote:
Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...


Aiwa AD WX888 , 1997,I worked on once, spindle to one capstan 2.49mm
diameter and the other 2.69mm

Aiwa ADR470, forward flywheel was inside the loop, reverse was outside
the loop. Both always driven. choice of pinch rollers determine
direction. Flywheel diameters compensate for inside/outside belt
diameter. Only speed adjustment was screw-driver inside the motor
housing itself.

Harman Kardon HK300 had a single flyheel, spindle impressed
alternately on fw or rev through a clutch that was always
disintegrating. Same in-the-motor adgustment.

RL

 

[M Philbrook]

In article <nc0r83$tjh$1@dont-email.me>, ham789@netzero.net says...

On 3/12/2016 12:36 AM, Look165 wrote:
One (the small one) is the motor capstan.

The other one is the pressure capstan.

Direction is given by the rotation of the first one and speed is
servo-controlled.

Generally there is a lever for the tension of the tape.


DaveC a écrit :
Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette
mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...


The tape speed is controlled by the motor drive capstan.
Doesn't matter which way the tape is going.
The two flywheels are different sizes, but have the same
rotation speed. That causes the belt to
stretch on one side and compress on the other to account for
the different sizes. That belt tension creates the tape tension.
That's independent of the direction of the rotation.
Tape speed across the heads is always controlled by the drive motor.

Really?

Then what is the use of that little pinch roller and drive shaft that
the tape fits between, for?

Jamie

 

[John Larkin]

On Sat, 12 Mar 2016 13:06:27 -0500, legg <legg@nospam.magma.ca> wrote:

On Sat, 12 Mar 2016 17:37:50 +0000, N_Cook <diverse@tcp.co.uk> wrote:

On 11/03/2016 21:22, DaveC wrote:
Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...


Aiwa AD WX888 , 1997,I worked on once, spindle to one capstan 2.49mm
diameter and the other 2.69mm

Aiwa ADR470, forward flywheel was inside the loop, reverse was outside
the loop. Both always driven. choice of pinch rollers determine
direction. Flywheel diameters compensate for inside/outside belt
diameter. Only speed adjustment was screw-driver inside the motor
housing itself.

Harman Kardon HK300 had a single flyheel, spindle impressed
alternately on fw or rev through a clutch that was always
disintegrating. Same in-the-motor adgustment.

RL

All those mechanical means of reproducing sound - wax disks, tinfoil,
shellac, plastic, wire, tape - were all awful. Chemical photography
was a nuisance, too. Ditto typing and carbon paper.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Martin Riddle]

On Sat, 12 Mar 2016 12:19:34 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sat, 12 Mar 2016 13:06:27 -0500, legg <legg@nospam.magma.ca> wrote:

On Sat, 12 Mar 2016 17:37:50 +0000, N_Cook <diverse@tcp.co.uk> wrote:

On 11/03/2016 21:22, DaveC wrote:
Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...


Aiwa AD WX888 , 1997,I worked on once, spindle to one capstan 2.49mm
diameter and the other 2.69mm

Aiwa ADR470, forward flywheel was inside the loop, reverse was outside
the loop. Both always driven. choice of pinch rollers determine
direction. Flywheel diameters compensate for inside/outside belt
diameter. Only speed adjustment was screw-driver inside the motor
housing itself.

Harman Kardon HK300 had a single flyheel, spindle impressed
alternately on fw or rev through a clutch that was always
disintegrating. Same in-the-motor adgustment.

RL

All those mechanical means of reproducing sound - wax disks, tinfoil,
shellac, plastic, wire, tape - were all awful. Chemical photography
was a nuisance, too. Ditto typing and carbon paper.

Yeah but look at the bit-error rate you can tolerate.
A CD would be worth less with that many errors.


Cheers

 

[DaveC]

On 12 Mar 2016, John Larkin wrote:

All those mechanical means of reproducing sound - wax disks, tinfoil,
shellac, plastic, wire, tape - were all awful. Chemical photography
was a nuisance, too. Ditto typing and carbon paper.

Yeah, yeah, yeah.

Gotta have a source platform in order to digitize all that media...

 

[Phil Allison]

MJC wrote:

Sure, but my point was that any chatter in the bearings is just as bad
as rotational variation and is not damped by the flywheel. So the plain
bearings have to be accurate and long-lasting.


** You have completely forgotten the damping effect of side-ways
pressure from the pinch roller.


I certainly was not taking it into account. Probably because it is
movement along the length of the tape and not sideways that gives rise
to speed modulation at the pick-up.

** Just to rub it in, the SIDEWAYS pressure from the pinch roller forces the capstan shaft against the bearing and inhibits any "chattering".

I really works and I see machines ( ie Roland Space Echos) with noticeable play in the capstan bearing that have low W&F.


..... Phil

 

[Phil Allison]

DaveC wrote:

By my mind that is backward: the pinch roller is passive (not being driven).
The capstan shaft (~2mm diam) is driven by capstan flywheel/belt/motor
pulley.

** Tape speed is determined by the surface speed of the motor pulley divided by the flywheel to capstan diameter ratio.

That ratio might be 20:1 making the pulley surface speed 37.5 inches/S for a standard cassette speed of 1-7/8 inches/S.


..... Phil

 

"The capstan is a passive device. The motor pulley diameter via the >*pinch roller* determines the tape speed. The capstan wheel can be >any size at all.

Peter Wieck
Melrose Park, PA "

Absolutely false. the pinch roller can be any damn diameter is want. The tape speed is controlled by the driven element of the system which is that capstan and is exactly its RPM times its diameter and of course Pi.

Alot of people misunderstand this, especially in the US. Same thing with the idler wheel on a turntable, it can be bigger or smaller, doesn't mean shit. the ratio that matters there is the motor to the rim, which is the driven element. On tape, the speed is precisely controlled by the capstan and that is based on the capstan diameter. ONLY. The pinch roller can be as big as a truck tire and it still goes the same speed.

Y'know, when I was in school they gave me this test. Turns out I was in the 99th percentile in mechanical reasoning. I liked that part of the test, gears n shit. When I started corresponding internationally, I thought that too high. People in some countries are smart as all hell. So in the world maybe I am just a 50. But the thing is, here we got guys who cannot figure out how to change a flat tire. (tyre for you oppressive folks across the pond we had to kick out of our jungle because of your damn taxes)

I did not learn any of this shit in schools. The schools here don't teach that useful information, or as far as I could see any useful information. You can plainly see those flywheels move in opposing directions, but there was a disconnect. I can't fault people for that, it is a deficiency in their education. In this country, peoples' Parents worked too fucking much and thought the schools would teach their kids. Didn't work.

I am not trying to put anyone down, I understand how it is, but the bottom line is this question should never have been asked.

 

[Look165]

Wrong !

The linear speed is RPM/60*pi*D (D in meter), eventually *100 if it's
given in cm/s ; for a cassette it is 4,75 cm/s.
It is determnied by the little axis that tha tape is pinched to.



jurb6006@gmail.com a écrit :

"The capstan is a passive device. The motor pulley diameter via the >*pinch roller* determines the tape speed. The capstan wheel can be >any size at all.

Peter Wieck
Melrose Park, PA "

 

"I can imagine a method that used heat to move the air, perhaps with >a
plasma to make it fast. "

The singing arc.

However it depends on how you want to be about this. If someone want no moving parts that is fine and the singing arc works for that.

But your eardrum still moves as well as the linage from it to the cochlea.

Plus the fact that the air itself moves.

 

[legg]

On Sat, 12 Mar 2016 12:19:34 -0800, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sat, 12 Mar 2016 13:06:27 -0500, legg <legg@nospam.magma.ca> wrote:

On Sat, 12 Mar 2016 17:37:50 +0000, N_Cook <diverse@tcp.co.uk> wrote:

On 11/03/2016 21:22, DaveC wrote:
Oh, smarter-than-I people,

http://imgur.com/WPEoOu1

The 2 belt-drive capstan flywheels in an auto-reverse cassette mechanism are
different sizes. (Motor drive pulley will be in the small loop end of the
belt in illustration above.)

How does that result in the same tape speed in both directions?

Confused...


Aiwa AD WX888 , 1997,I worked on once, spindle to one capstan 2.49mm
diameter and the other 2.69mm

Aiwa ADR470, forward flywheel was inside the loop, reverse was outside
the loop. Both always driven. choice of pinch rollers determine
direction. Flywheel diameters compensate for inside/outside belt
diameter. Only speed adjustment was screw-driver inside the motor
housing itself.

Harman Kardon HK300 had a single flyheel, spindle impressed
alternately on fw or rev through a clutch that was always
disintegrating. Same in-the-motor adgustment.

RL

All those mechanical means of reproducing sound - wax disks, tinfoil,
shellac, plastic, wire, tape - were all awful. Chemical photography
was a nuisance, too. Ditto typing and carbon paper.

I can't think of a single method of 'reproducing sound' that doesn't
involve mechanical means.

Sound is a mechanical phenomenon. Humans use flapping meat.

Perhaps you mean recording? No, still mechanical. Storage? Maybe.

Of course, there's nothing mechanical in electronics, is there...

It's the programme material, the idea and its conception that's
important; not the means of conveyance.

RL

 

[DaveC]

On 12 Mar 2016, jurb6006@gmail.com wrote
(in article<ad5cfe86-5261-4c1f-9194-4771564fe740@googlegroups.com&gt:

I am not trying to put anyone down, I understand how it is, but the bottom
line is this question should never have been asked.

OK I’ve learned from you how to determine tape speed by measuring the
capstans.

But you have not answered the question (that apparently should never have
been asked) why the 2 flywheels are different sizes.

(op)

 

[MJC]

In article <2m0beb1lgja42278t1ni529ihahvjsc94q@4ax.com>,
legg@nospam.magma.ca says...

I can't think of a single method of 'reproducing sound' that doesn't
involve mechanical means.

Sound is a mechanical phenomenon. Humans use flapping meat.

I can imagine a method that used heat to move the air, perhaps with a
plasma to make it fast. (Like a modulated lightning flash.) But I cannot
be bothered to construct a search to find out if it has been done
successfully...

Mike.

 

[Don Bruder]

In article <MPG.314f98caaaa273144@news.plus.net>,
MJC <gravity@mjcoon.plus.com> wrote:

In article <2m0beb1lgja42278t1ni529ihahvjsc94q@4ax.com>,
legg@nospam.magma.ca says...

I can't think of a single method of 'reproducing sound' that doesn't
involve mechanical means.

Sound is a mechanical phenomenon. Humans use flapping meat.

I can imagine a method that used heat to move the air, perhaps with a
plasma to make it fast. (Like a modulated lightning flash.) But I cannot
be bothered to construct a search to find out if it has been done
successfully...

Mike.

I recall a conversation from years ago with a *VERY* old theater
projectionist, who spoke of what he called "flame speakers". Don't know
if it was an artifact of his (at the time) 80+ year old mind going, or
reality, but what he described made sense to me on several levels,
though I've never bothered to try chasing it down. Apparently, back in
the early days of talkies, one method of sound production involved a gas
nozzle (unsure if he meant gasoline, or something like propane/LP gas)
"tuned" to produce a blue flame (he was very clear on that point - lots
of the conversation came back to how he had to tinker with the flame at
each showing, otherwise the sound wasn't good) several feet tall in a
combustion chamber, into which was shoved a set of tungsten electrodes.
The 'trodes were driven at high voltages by any of several amplification
methods (frequently varying by theater, if the old guy's tale was to be
believed) to charge the plasma of the flame, which apparently caused it
to "dance", driving a diaphragm like that of a speaker. Supposedly,
amazingly high volumes with very good fidelity could be achieved.

Like I say, I've never actually gone to the effort of tracking it down,
and I have no idea if it was a failing mind's invention, or reality,
but... <shrug> Seems to me like it COULD work.

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