Turntable speed accuracy

Thanks Dover, Chris, Thuchan & Banquo,
I appreciate your encouragement :^)...... John Gielgud (blush).
Dover is from New Zealand.....so of course I sound like an orator to him:^)

I was going to follow up with a video of the Raven AC-3 under test.......but I don't think it's fair?
Everyone can test his own turntable once armed with the Timeline.
There will be some shocks?

Tony,
The TT-101 does in fact reach its correct speed within a revolution as seen on the Timeline.
The actual specification states that 'starting time' is within 0.6sec.
Starting torque: 1.2Kg/cm
Speed deviation: 0.002%
Drift: 0.0004%

There appears to be some confusion about the functioning of the quartz locked positive and negative servo control of the TT-101?
It does not compensate for a speed deviation over a complete 'revolution' or series of 'revolutions'.
In other words......if there is a slowing down due to stylus drag........the servo does NOT speed up to 'compensate' for that 'lost' time and thus keep an 'average' continuum?
The servo does not know how many revolutions it is completing in any listening session....nor does it care.
It cares only about 'instantaneous' micro speed control.
What this means, is that if there were a slow-down due to stylus drag at any point of a record's playing cycle......that error would be permanently imprinted on the Timeline 'Blutak' marker on the wall. And any extra deviations would be accumulative so that the laser line of the Timeline would 'drift' further to the left with every revolution.
This you will appreciate if you ever use your own Timeline on your own turntable?
It truly puts into perspective the performance of the TT-101 which you have witnessed on the video?

H Lewm, yes, you are correct. That is called cogging. I'm sure BD motors do it too if they are unloaded. You just can't see it with your eyes because they spin too fast. That is what I was saying before that designers use mass as a damper- mass damping. All motors have some level of cogging, or ripple. Even your car engine has it as each piston fires. The flywheel smoothes out those ripples just as the tt platter smoothes out the ripples from the motor. The typical tt specs showing Wow&Flutter below 0.03% shows how well these massive platters are doing their job. btw, the more poles that a motor has, the smaller the ripples. I notice some of these expensive tables have quite sophisticated motors. Caveat Emptor always applies, but I think you are getting what you pay for in some of these expensive motor designs.

Tony you may find Dovers record player interesting ,surely a heavy weight contender for ultra sophisticated speed control.

Henry if my memory is correct I seam to think that I read somewhere TW Acustics stated their motor speed control was designed to perform like a vintage direct drive.

Dear Tony, Cogging is indeed a problem with motors, but what I described would not be strictly due to cogging. Mostly it is due to the servo hunting when its feedback loop is screwed up by the lack of a platter mass or in the other extreme, too much platter mass. Cogging will always be there and is an inherent property of the motor; some are less prone to cogging than others.