Why are capstan wheels different size?

[DaveC]

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...

 

[Phil Allison]

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

 

[Jasen Betts]

On 2016-03-11, DaveC <not@home.cow> 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?

do they have the same capstan diameter?

--
\_(ツ)_

 

[M Philbrook]

In article <0001HW.1C936E810003F2001244403CF@news.eternal-
september.org>, not@home.cow says...

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...

Its been a while since I've seen the inside of a cassett drive.

But memory tells me you have a pinch roller with pin shaft that governs
the actual speed.

Jamie

 

[Les Cargill]

M Philbrook wrote:

In article <0001HW.1C936E810003F2001244403CF@news.eternal-
september.org>, not@home.cow says...

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...

Its been a while since I've seen the inside of a cassett drive.

But memory tells me you have a pinch roller with pin shaft that governs
the actual speed.

Jamie

Yep.

--
Les Cargill

 

[MJC]

In article <MPG.314d1a13f8dcab69989eb1@news.eternal-september.org>,
jamie_ka1lpa@charter.net says...

Its been a while since I've seen the inside of a cassett drive.

But memory tells me you have a pinch roller with pin shaft that governs
the actual speed.

Jamie

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...

Mike.

 

[DaveC]

Jasen Betts asked wisely:

> do they have the same capstan diameter?

I was just about to say “Silly question!” but instead thought better...

one 2mm, one 2.2mm

I guess the difference is driven (c; by the fact (stated by Phil) that the
flywheels are different diameters to discourage mechanical resonance.

Thanks Jasen!

 

[Tim Wescott]

On Fri, 11 Mar 2016 13:22:09 -0800, 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...

Presumably the belt speed changes, or the capstains themselves are
different diameters.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

On Friday, March 11, 2016 at 1:22:14 PM UTC-8, 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...

Looks like my Nakamichi cassette deck. They used 2 different sdiameter
capstans / flywheels running at different RPMs BUT the same tape speed
closed loop drive (both pinch rollers always engaged). They said they did
that so that the capstans won't slowly go in and out of phase which causes
wow and flutter to go up and down. By running different RPMs they go in and
out of sync so quickly we don't notice it. As the belt stretches and
contracts around the flywheels, the lead capstan will alway run slightly
faster (tape speed wise) than the trailing capstan which keeps the tape
tension correct on an auto reverse machine regardless of the direction. My
deck is only single direction and the wow/flutter is nearly imperceptible.

Then I went digital so who cares about cassettes?

G˛

 

Because of the thickness of the belt.

 

"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. 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.

 

[Phil Allison]

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.

** You on crack ??

 

[Phil Allison]

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

 

[Phil Allison]

jurb...@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

** Self evidently false.

Yawnnnnnnnnnn................


.... Phil

 

[pfjw@aol.com]

On Friday, March 11, 2016 at 4:22:14 PM UTC-5, 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...

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

 

[Look165]

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...

 

[DaveC]

> Then I went digital so who cares about cassettes?

Need a source to digitize the analogue media...

 

[Adrian Caspersz]

On 12/03/16 08:42, stratus46@yahoo.com wrote:

On Friday, March 11, 2016 at 1:22:14 PM UTC-8, 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...

Looks like my Nakamichi cassette deck. They used 2 different sdiameter
capstans / flywheels running at different RPMs BUT the same tape speed
closed loop drive (both pinch rollers always engaged). They said they did
that so that the capstans won't slowly go in and out of phase which causes
wow and flutter to go up and down. By running different RPMs they go in and
out of sync so quickly we don't notice it. As the belt stretches and
contracts around the flywheels, the lead capstan will alway run slightly
faster (tape speed wise) than the trailing capstan which keeps the tape
tension correct on an auto reverse machine regardless of the direction. My
deck is only single direction and the wow/flutter is nearly imperceptible.

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.

--
Adrian C

 

[mike]

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.

 

[N_Cook]

On 12/03/2016 03:49, DaveC wrote:

Jasen Betts asked wisely:

do they have the same capstan diameter?

I was just about to say “Silly question!” but instead thought better...

one 2mm, one 2.2mm

I guess the difference is driven (c; by the fact (stated by Phil) that the
flywheels are different diameters to discourage mechanical resonance.

Thanks Jasen!

May seem pedantic , but there is a rationale.
Having been here before, to standardise to using a strobe to set tape
speed, in the absence of a test tape of known goodness, ie not
stretched, as the people wanting cassette players repaired these days
tend to be musically on the ball as regards being perfect pitch.
You'll probably find the spindle diameters are 1.99mm and 2.19mm .
I got a precision mechanical engineer to measure a dozen or more random
spindles and they were all *.*9 mm , presumably because the available
bearings are *.*0 mm