In article
,
Tim+ wrote:
I would agree that it introduces a new ”weak point• in the braking system
though. Off the top of my head, Jaguar E-type, Rover 2000/3,500 and
Citroen ZX all had inboard discs,.

Did they have a reputation for snapping drive shafts?

One of the main problems is providing adequate cooling with inboard brakes.

--
*With her marriage she got a new name and a dress.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 19 Feb 2018 00:15:00 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
Yes - remember a pretty advanced design of 1/4" tape recorder. Had
twin capstans with direct drive. And they stopped turning when the
tape stopped running. They were pancake motors. Had a very fast start
up time. That would explain it.

The fast startup times were more probably the result of employing
solenoid operated pinch wheels. I'm sure the capstan motors were more
likely kept spinning all the time the machine was powered up and ready
to go.

No. As I said, the motors stopped. Constant run capstan was the far more
common method.

Presumably, in this case, pressing the play button immediately powers
the capstan motor but delays the pinch wheel solenoid operation by a few
tens of milliseconds to allow the capstan motor to get up to speed.
Pressing the stop button would simultaneously release the pinch wheel
solenoid and shut off the capstan motor.

I modified my Akai GX630DB to allow the end of tape lever arm micro-
switch to disable the direct drive capstan motor as well as put the
machine into a stopped state. Prior to the modification, the capstan was
left spinning all the time the machine was powered up which seemed an
unnecessary extra burden of wear on a critical component, hence the
modification.

In this case, there was no call for any fancy timing delays since once a
tape was laced up and the slack taken up to ready the machine, the
capstan motor would have long since come up to speed before hitting the
play button or unpausing it and, provided the tape didn't run out or was
deliberately slackened off, the capstan motor would just keep running as
before.

The myths regarding the effect of gravity on the bearings of non-
spinning motors seemed to be just that. Why would leaving the motor
spinning *only* whilst the machine was powered up and yet not able to run
when powered down, perhaps for days or even months at a time, mitigate
against such a mythical effect? Answer: it couldn't.

--
Johnny B Good

In article ,
Johnny B Good wrote:
No. As I said, the motors stopped. Constant run capstan was the far more
common method.

Presumably, in this case, pressing the play button immediately powers
the capstan motor but delays the pinch wheel solenoid operation by a few
tens of milliseconds to allow the capstan motor to get up to speed.
Pressing the stop button would simultaneously release the pinch wheel
solenoid and shut off the capstan motor.

I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

--
*Happiness is seeing your mother-in-law on a milk carton

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 19 Feb 2018 11:14:10 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
No. As I said, the motors stopped. Constant run capstan was the far
more common method.

Presumably, in this case, pressing the play button immediately powers
the capstan motor but delays the pinch wheel solenoid operation by a
few tens of milliseconds to allow the capstan motor to get up to speed.
Pressing the stop button would simultaneously release the pinch wheel
solenoid and shut off the capstan motor.

I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

The dual capstan system used by upmarket dual capstan cassette decks
relied on the use of belt drive to provide an effective tape tension
between the two capstans. I can't quite see how two synchronised direct
drive capstans could achieve this without limiting the deck to forward
only play (and record), with a slightly smaller diameter capstan on the
entry side to create the required tape tension between them.

BTW, are you talking about reel to reel or cassette? Also, how did the
pause mechanism work in this system? I'm assuming whichever it was would
have had a pause lever or button to allow an instant acceleration to
'speed'.

It would need an extremely low inertia direct drive capstan motor to
match the tape speed acceleration to speed from engaging the pinch wheel
onto an already up to speed capstan which seems counterproductive to the
need to minimise capstan flutter by use of the flywheel effect normally
incorporated into most direct drive capstan motor designs (the reason why
they're normally left to run at their selected speed all the time that
the deck is powered up).

--
Johnny B Good

In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.

It was a pro 1/4".

--
*Those who live by the sword get shot by those who don't*

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 20 Feb 2018 10:28:10 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive,
the speed the pinch rollers came in might be a problem to match. But
the motors were sync'd so I'd guess the solenoids came in first then
the motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.

It was a pro 1/4".

In which case, the capstan motors weren't being synchronised in the
conventional sense. The electronics must have been used to set up the
tiny (and appropriate) speed differential required to generate the
required tension in the section of tape passing the heads. Clever
electronics indeed.

I suppose such clever (or 'smart') electronics could easily include
accurately timed solenoid control of the pinch wheels to allow for the
effect of 'run up time' (no matter how brief) to eliminate the start and
stop pitch slide effect.

Whilst extremely low inertia motors can be made by making the rotor
'ironless' using a rotor made entirely from just the copper wire formed
into a moving coil shape[1] by the use of an epoxy glue, this doesn't
seem to be a good idea when you want to eliminate flutter from even the
most residual of commutation/cogging effects on the motor's angular speed.

Since you need to use pinch wheels for reasons other than to achieve
'instant' stop/start anyway (to prevent deformation of the pinch wheel
rubber tyre and to allow the tape to be threaded), I don't see tape deck
manufacturer choosing an 'inertialess' motor design for this application.

The "Engaging a pinch wheel onto or off a constantly spinning capstan"
technique still offers a tried and tested method to achieve the near
instantaneous stop/start characteristic of 'pause/unpause' we've all
become accustomed to using on even the most humblest of tape transport
mechanisms.

Cassette decks rely entirely on its very slow transport speed and the
tape's elasticity to absorb the brief start up acceleration forces
required to bring the supply spool up to speed but open reel tape decks
designed for much higher transport speeds typically[2] get round this
issue by including additional damped tensioning arms in the supply reel
to capstan path to both absorb the higher forces involved and to
effectively isolate the section of tape passing the record/replay heads
from the high G force involved in using a pinch wheel to 'instantly'
accelerate that critical section of tape up to speed.

I'm not saying such instant start, direct drive, capstan motors are
impossible, just that they seem an improbable solution in this case
(BICBW).

[1] More likely in this case, a disk shape to form the rotor of a
'pancake' motor.

[2] I use the qualifier, "typically" because very highly specified
capstan driven[3] tape transport mechanisms use a variety of active servo
control methods to buffer the critical tape path section from the
mechanical loading effects of both the supply and the takeup spools
(reels).

[3] I make this distinction because there are some very high speed
magnetic tape data recorders where the tape speed is too fast to make
capstan drive a viable option. In this case, tape spool drive is used as
a controlled version of the fast forward and reverse modes used by
conventional tape drives where the data flows are buffered to allow short
term adjustments of the supply and takeup spool rotational speeds to the
correct average linear tape speed via servo control in a similar fashion
to the control of the spin speed of an audio CD player disk.

--
Johnny B Good

On Tuesday, 20 February 2018 18:44:05 UTC, Johnny B Good wrote:
On Tue, 20 Feb 2018 10:28:10 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive,
the speed the pinch rollers came in might be a problem to match. But
the motors were sync'd so I'd guess the solenoids came in first then
the motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.

It was a pro 1/4".

In which case, the capstan motors weren't being synchronised in the
conventional sense. The electronics must have been used to set up the
tiny (and appropriate) speed differential required to generate the
required tension in the section of tape passing the heads. Clever
electronics indeed.

I suppose such clever (or 'smart') electronics could easily include
accurately timed solenoid control of the pinch wheels to allow for the
effect of 'run up time' (no matter how brief) to eliminate the start and
stop pitch slide effect.

Whilst extremely low inertia motors can be made by making the rotor
'ironless' using a rotor made entirely from just the copper wire formed
into a moving coil shape[1] by the use of an epoxy glue, this doesn't
seem to be a good idea when you want to eliminate flutter from even the
most residual of commutation/cogging effects on the motor's angular speed.

Since you need to use pinch wheels for reasons other than to achieve
'instant' stop/start anyway (to prevent deformation of the pinch wheel
rubber tyre and to allow the tape to be threaded), I don't see tape deck
manufacturer choosing an 'inertialess' motor design for this application.

The "Engaging a pinch wheel onto or off a constantly spinning capstan"
technique still offers a tried and tested method to achieve the near
instantaneous stop/start characteristic of 'pause/unpause' we've all
become accustomed to using on even the most humblest of tape transport
mechanisms.

Cassette decks rely entirely on its very slow transport speed and the
tape's elasticity to absorb the brief start up acceleration forces
required to bring the supply spool up to speed but open reel tape decks
designed for much higher transport speeds typically[2] get round this
issue by including additional damped tensioning arms in the supply reel
to capstan path to both absorb the higher forces involved and to
effectively isolate the section of tape passing the record/replay heads
from the high G force involved in using a pinch wheel to 'instantly'
accelerate that critical section of tape up to speed.

I'm not saying such instant start, direct drive, capstan motors are
impossible, just that they seem an improbable solution in this case
(BICBW).

[1] More likely in this case, a disk shape to form the rotor of a
'pancake' motor.

[2] I use the qualifier, "typically" because very highly specified
capstan driven[3] tape transport mechanisms use a variety of active servo
control methods to buffer the critical tape path section from the
mechanical loading effects of both the supply and the takeup spools
(reels).

[3] I make this distinction because there are some very high speed
magnetic tape data recorders where the tape speed is too fast to make
capstan drive a viable option. In this case, tape spool drive is used as
a controlled version of the fast forward and reverse modes used by
conventional tape drives where the data flows are buffered to allow short
term adjustments of the supply and takeup spool rotational speeds to the
correct average linear tape speed via servo control in a similar fashion
to the control of the spin speed of an audio CD player disk.

minor point: not all cassette decks had an always on motor. It was never judtifiable for battery powered decks, and some mains decks didn't either.


NT

In article , Dave Plowman (News)
scribeth thus
In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.



It was a pro 1/4".


Which make and model was that Dave?....

--
Tony Sayer

On Tue, 20 Feb 2018 11:26:23 -0800, tabbypurr wrote:

====snip====


minor point: not all cassette decks had an always on motor. It was never
judtifiable for battery powered decks, and some mains decks didn't
either.

True enough. I just didn't think to include them. They're the type that,
when the operator forgets to use the pause function when recording before
engaging the play/record mode, will give that characteristic down pitch
squeak at the beginning of a recording (and the reverse effect at the end
if the pause function is yet again ignored).

I'm pretty certain that very few, if any, mains powered tape recorders
lacked a pause feature and likewise even cheap battery powered cassette
recorders (although to listen to some 60s and 70s documentary film sound
tracks, you might think it was otherwise).

Even so, only allowing the capstan to spin up when play or record mode
had been selected, wasn't normally a problem if it had a pause feature
(provided the user thought to make use of it for recordings - it's
generally not so critical in the case of playback).

Having said that, I wonder if I was getting a little at cross-purposes
in my discussion with Dave by assuming the pause functioned as he
described the normal play function which isn't as critical as getting an
instant start by using the pause to start a recording. I'm sure his 1/4
inch reel to reel deck would have a pause function which makes my
arguments rather academic. After all, such startup artefacts aren't
really a problem with playback, only recording where you'd use the pause
function to all but eliminate the problem anyway.

--
Johnny B Good

On Tuesday, 20 February 2018 20:46:07 UTC, Johnny B Good wrote:
On Tue, 20 Feb 2018 11:26:23 -0800, tabbypurr wrote:

====snip====


minor point: not all cassette decks had an always on motor. It was never
judtifiable for battery powered decks, and some mains decks didn't
either.

True enough. I just didn't think to include them. They're the type that,
when the operator forgets to use the pause function when recording before
engaging the play/record mode, will give that characteristic down pitch
squeak at the beginning of a recording (and the reverse effect at the end
if the pause function is yet again ignored).

I'm pretty certain that very few, if any, mains powered tape recorders
lacked a pause feature and likewise even cheap battery powered cassette
recorders (although to listen to some 60s and 70s documentary film sound
tracks, you might think it was otherwise).

Even so, only allowing the capstan to spin up when play or record mode
had been selected, wasn't normally a problem if it had a pause feature
(provided the user thought to make use of it for recordings - it's
generally not so critical in the case of playback).

the worst decks from the 70s had startup speed problems, but 80s decks with switched motors normally didn't. They made it work ok. Even some budget hifi had switched motors, eg JVC.


NT

In article ,
Johnny B Good wrote:
No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.

It was a pro 1/4".

In which case, the capstan motors weren't being synchronised in the
conventional sense. The electronics must have been used to set up the
tiny (and appropriate) speed differential required to generate the
required tension in the section of tape passing the heads. Clever
electronics indeed.

Quite. So not in exact sychronisation, but a degree of offset.

I suppose such clever (or 'smart') electronics could easily include
accurately timed solenoid control of the pinch wheels to allow for the
effect of 'run up time' (no matter how brief) to eliminate the start and
stop pitch slide effect.

Whilst extremely low inertia motors can be made by making the rotor
'ironless' using a rotor made entirely from just the copper wire formed
into a moving coil shape[1] by the use of an epoxy glue, this doesn't
seem to be a good idea when you want to eliminate flutter from even the
most residual of commutation/cogging effects on the motor's angular
speed.

I have seen one in bits, but can't really remember the motor design -
except it was pancake shaped.

It was certainly ahead of its time in terms of a very stable transport.
You could lock a colour VTR to it and edit pictures exactly where needed
(within the limits of the PAL system) Which was very handy for doing dance
etc numbers to pre-recorded music with multiple passes. It was some time
before the likes of Studer caught up with the more conventional single
capstan design.

Its other trick was you could use any size of spool on either side with
zero problems.

--
*What boots up must come down *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.



It was a pro 1/4".


Which make and model was that Dave?....

Klark Teknik, in the late 70s. I've a feeling it caused them financial
problems then - but think they are still around.

--
*Hard work pays off in the future. Laziness pays off now *

Dave Plowman London SW
To e-mail, change noise into sound.

On Wed, 21 Feb 2018 00:06:05 +0000, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:

====snip====


Whilst extremely low inertia motors can be made by making the rotor
'ironless' using a rotor made entirely from just the copper wire formed
into a moving coil shape[1] by the use of an epoxy glue, this doesn't
seem to be a good idea when you want to eliminate flutter from even the
most residual of commutation/cogging effects on the motor's angular
speed.

I have seen one in bits, but can't really remember the motor design -
except it was pancake shaped.

It was certainly ahead of its time in terms of a very stable transport.
You could lock a colour VTR to it and edit pictures exactly where needed
(within the limits of the PAL system) Which was very handy for doing
dance etc numbers to pre-recorded music with multiple passes. It was
some time before the likes of Studer caught up with the more
conventional single capstan design.

Its other trick was you could use any size of spool on either side with
zero problems.

Probably done by threading the tape between a pair of guide pins on a
small 'turntable' either side of the capstans. These rotating turntables
were spring loaded and drove either a potentiometer or some optical
position sensor to generate a control signal to the reel table motors so
as to regulate the back and the take up tensions generated by a constant
current source drive to these motors.

The system used by the GX630DB (and possibly also the GX747) wasn't
quite so sophisticated. They both used direct drive reel table motors
with a constant current drive to provide the necessary tape tensions but
relied on a reel size selector switch to provide a fixed level of torque
which was a compromise for 7 and 10 inch reels which was far from ideal
with 3 and 4 inch reels, especially when loaded with triple play tape[1]!

This, of course is just one example of a servo controlled tape
tensioning system. The other, near identical version you'd likely see
differed only in that the tension sensing arms would simply be a single
guide pin on the end of a spring tensioned swinging arm or a sprung
loaded slider in a guide slot which drove a pot or optical position
sensor.

Ultimately, seen only in high speed open reel reel data storage systems,
you had the tape loaded into pneumatic silos[2] either side of the head/
capstan assembly (capstan in this case not always required) with some
form of sensing to maintain the amount of tape in the loop of tape being
held by air pressure/vacuum in the silos by bi-directional control of the
reel table motors (the supply/takeup reel tables not only provided back
tension but were actively accelerated in the opposite sense to eliminate
any excess back tension from attempts to accelerate the tape pack from
tape tension alone. This truly did isolate the critical section of tape
passing the read/write heads from the effects of inertia in the supply
and take up spool drive system.

[1] When I was creating my own Absolute Azimuth White Noise Calibration
test tapes some thirty odd years ago, I took advantage of the extremely
thin triple play tape which allowed it to be flipped over and played in
the opposite direction so as to play back the stereo in phase from a mono
noise source recording via the back side of the tape. With a 4 track
stereo tape deck, it was most vital to have the left and right head gaps
in perfect alignment if you wished to retain mono mixdown compatibility
with other, equally correctly lined up tape decks. The effect of "Head
Scatter" was of minor importance in this case.

It took only just three or four iterations of such testing to arrive at
an absolutely correct Azimuth setting of the record and playback heads
from which I was then able to create several copies on 7 and 10 inch
reels of LP tape. Since the only suitable triple play tape I possessed
was loaded onto 3 inch reels, this presented a huge tape tensioning
issue. I got round this by winding the tape over a 7 inch reel full of
tape to act as a large diameter 'hub' where I could select the 10 inch
reel tensioning option to approximate a back tension better suited to
such thin tape.

Loading a 3 inch reel's worth of tape over the top of a full 7 inch reel
wasn't a problem since there was still adequate space on the full reel to
add the additional tape without going beyond the limits of the reel. This
also made it easier to deal with the business of re-loading the tape 'the
wrong side up' to complete the auditioning phase of the adjustment
process where the mono mixdown, though muffled, would allow me to
determine whether I'd reached the optimal point of absolute azimuth that
would generate the highest tone of 'hiss' without still having to
temporarily nudge the replay head gently either side of its current
alignment to prove which way, if any, the optimum setting lay.

If a nudge to the left was required to find this point, I'd adjust the
head azimuth by half this required amount before repeating the test
recording process with the tape reloaded the right way around and then
having another listen to the result. I think the initial iterations were
done by simply swapping the reels over and twisting the tape over between
the reels and the first guides. Literal reloading the tape the 'wrong
side out' onto the reels was left for the final stages to verify the
result without imposing a possibly detrimental effect arising out of
using the twisted tape path method.

I think I created one or two dedicated test tapes but I also recall
making good use of the space after the end of several existing recordings
on some of my 7 and 10 inch reels of LP tapes where the recordings had
left a good 5 minutes or more of blank tape at the end where it would be
well out of the way when auditioning the recordings.

[2] These pneumatic silo tensioners were as close to an 'inertialess'
spring tensioning system as you could get since it got rid of the mass of
a typical tensioning arm and its spring, leaving only a few milligrams'
worth of tape mass and micrograms' worth of 'air spring' to upset the
dynamic tape tensioning forces in the critical section of tape being
scanned by the read/write heads. This really was the ultimate in tape
handling taken to the extreme!

Of course, such extremes weren't justified even with 24 track studio
decks but were par for the course in mainframe computer rooms where time
very much equalled money and extremely reliable high speed data tape
processing was the order of the day when, despite even such extremes of
performance, it still represented a bottleneck in the whole data
processing chain.

--
Johnny B Good

In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
In article ,
Johnny B Good wrote:
I'm not quite sure of the actual sequence. With twin capstan drive, the
speed the pinch rollers came in might be a problem to match. But the
motors were sync'd so I'd guess the solenoids came in first then the
motors ran.

I'd assumed contra rotating capstans for a reversomatic bi-directional
system rather than trying to maintain tape tension between two capstans
across the heads.

No. The idea was to get the very best tape contact to the heads. And
miniumum weave and flutter etc. A very clever design.

Both capstans were direct drive. And I assume clever electronics to
maintain the correct tape tension.



It was a pro 1/4".


Which make and model was that Dave?....

Klark Teknik, in the late 70s. I've a feeling it caused them financial
problems then - but think they are still around.

Seems they disappeared from making tape machines looks like Leveers Rich
effectively took them over...
--
Tony Sayer