Tables That Feature Bearing Friction

Hi again,
Mark Kelly is correct about the tension differential, provided the thread/belt does stretch and that there are frictional losses in the platter/bearing system. I don't think he said that slippage was neccessary, but rather that it was unavoidable in real life(maybe I got that wrong...)
Slippage can be avoided, idler, belt or tape creep can't.
My comment on the counterpulley symmetry relates to Dertonarm asking for a debate in the theoretical domain. I made it the sake of debating idealized concepts rather than compromised implementations(called reality), please take that into account.

A single constant airstream working against "wings" will cause cogging. Two(or more), 180°(x°) perfectly out of phase air vents with proper orientation of the wings will cancel the cogging(don't want to be responsible for the maschining of that one...). But this isn't all that different from a conventional multipole motor.
A single leaf and a one impulse(or 0,5, ...) per revolution is different. One could achieve the same without the complexity of an air supply, the turbulence issues, etc. by using a very heavy platter, direct driven with the motor being switched on only infrequently , be it for a very short duration or ramped up, then down again, but only when the speed drops below a set deviation threshold. Oops, I see the word feedback on the horizon, mmh...
The inertia of the platter will be an intergrator again, the constant motor noise/mechanical jitter will be exchanged for an occasional pulse and the bearing losses ought to be zero ideally.
Low frequency pitch stability will once again be less than perfect :-(
There again, it contains compromises... I'm still tempted to build such a device(and sell it for --- ONE GAZILLION DOLLARS, buahahaha...!).

A pulsed air supply with transfer function matched "wings" won't cause cogging IF you solve the problem of syncronisation(and if there was no such thing as turbulence, a.k.a. CHAOS).

Now back to "real" work :-)

Frank

P.S.: Related to the original post: There are at least 6 different currently manufactered turntables that partially rely on creating additional drag on the platter for maximum speed stability.

Please take into consideration in all discussion about what drive and platter weight that is is not alone about constant speed.
There is the "2nd system" (mentioned before ) and its energy transfer into the platter: - the act of extracting information from the groove by the stylus. There is more to the platter than (high) torque, inertia and constant speed.
It has to handle complex energy transfer (and/or damping) provided by the stylus demodulating the groove.
Bringing this into consideration will clarify some points which came up in the last posts by Berlinta and T_bone. The high mass platter plus the low tension thread made of aramide or similar will too give some answers, why there is no problem with vibration or resonance being transmitted or initiated by the thread.
As for the hypothesis of the high inertia (which is fully backed and put into "half-commercial" product by Jean Constant Verdier in his Magnum ) providing close to ideal constant speed, it would be helpful if Kirkus - who is respected by us all - could clarify or illustrate the point.
If I try it might soon become too dogmatic again.
I am on holiday now and will - randomly and infrequently - follow this thread, but I will make no personal remark to anyone anymore and will not answer to any directed to me either

The "air-pulse" drive (no pulse would exclude a problem) has some considerable problems while looking close to a theoretical ideal first. It not only will require considerably (really serious...) periphery, but indeed a "assist"-motor to bring the (high mass) platter to requested speed first and than de-coupling. The question is whether it really will provide a "better" drive mechanism - as fascinating as the idea itself is.

Lewm, regarding my belief in Dertonarm's contentions... if you look at the first paragraph of my second of two consecutive posts above, I state...

I, for one, am not at all convinced Mr. D is right (though I would love to listen to the table he created) about high mass BD (even though my preferred TT at home is a HM BD with slipping thread drive). I expect DD is probably 'better' because I expect it is easier to control the electromagnetic slippages than the mechanical ones.

Regarding Chris Brady's DD TT... in paragraph two of the first of those two consecutive posts, I state...

It is obvious through Chris' assertions here that he believes his new DD system, and perhaps others', improve(s) upon those highly-praised BD TTs). I am sure they do.

I, for one, would love to have the chance to listen to that TT. I am sure it is fabulous. All the anecdotal evidence points to a conclusion that he has made one of the top commercially available TTs out there. But your next point:

Rather, these are good data that have to be explained.

is the crux of what I was trying to get at. I believe that Mr D's point is that anecdotal evidence of one or two commercially available TTs sounding better than another couple of TTs is fine, wonderful, and nice, but beside the point. He has asked for technical arguments WHY DD should be less of a compromise when attempting to create the perfect TT and so far noone has come up with the technical arguments, the physics, or experimental results detailing why that should or could be so. I think he would welcome the philosophical debate. I know I would.

And yes, I think the escape clause for most of us will be to say that we haven't heard the best BD TTs or DD TTs out there. But again, for Mr D, that is beside the point. I may not agree with his assertion that high-mass thread-slippage BD TTs are the best method to approach perfection, but I have no science or experimentation to back up my disagreement, so instead I hope to learn.

Cheers,