Why are capstan wheels different size?

do they have the same capstan diameter?

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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.

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Les Cargill

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.

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

.... Phil

Jasen Betts asked wisely:

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!

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

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

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.

are

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?

Need a source to digitize the analogue media...

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.

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Adrian C

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.

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

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.

Because of the thickness of the belt.

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 me ans 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 reve rse 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.

** You on crack ??

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

.... Phil

:)

Those things are

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

Agreed.

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Adrian C