Turntable speed accuracy

Dear Thuchan,
The Victor TT-101 is quartz controlled direct drive and automatically runs at a true 33.3rpm or 45rpm.
It has pitch adjustment in 6hz increments in both positive and negative direction.....but I never use this feature.
The servo control is bi-lateral........it works to speed up AND slow down.
Most other servos only are capable of speeding up and then rely on natural friction (or stylus drag) to be detected as 'too slow'.......for it to 'then 'speed up'.
This natural time delay is too slow with too much speed variance to really be critically effective IMHO?
Do you notice this slow-down when the stylus lands.........on your Nakamichi as well as your belt drives?

My point is that inertia has to be addressed at the outset of a turntable's design, and that electronic speed control merely augments it.

Mosin, as inertia is directly related to mass and friction.....are you saying that heavy platters have inherently greater inertia than light ones?
If you are?.........how do you explain that the turntable in the Timeline video features the Fat Bob platter with a massive weight and slows down alarmingly when the the stylus hits the record?
Yet my TT-101 has a puny 2.0 Kg cast aluminium platter which has zero deviation in speed with one, two or three cartridges lowered onto the same record?
All speed control is via the direct drive with servo control.
This instantaneous speed control I believe, is far more critical than inertia?

Henry - I want to see a youtube of the 3 cartridges lowered onto the record at the same time. :>)

I found an article online about the Nak. Very interesting tt. The author had an excerpt from an interview with the designer. He substantiates my point exactly. He says vinyl record runout is the elephant in the room that tt designers ignore. As for inertia: Torque= J*omega, which is the angular term for F=ma. The tt motor provides the torque and the platter bearing and stylus apply a counter torque. The inertia of the platter determines the rate of change in speed (deceleration). Say for example the motor is uncoupled from the platter. The platter is spinning at 33.33 rpm. (ignore bearing friction for a moment) Now drop the stylus onto the record. A 20 kg platter is going to decelerate at a lower rate, for example, than a 2 kg platter.
Now let's hook the motor back up to our platter. The motor is either clocked to the 60Hz line frequency or is feedback servo controlled. So it holds the platter at 33.33 rpm. Any perturbation in the platter speed causes the torque output of the motor to change in order to restore 33.33 rpm. The motor could do it's job regardless of the amount of inertia in the platter. The stability of the platter speed is based on the control loop and torque of the motor combined with the system inertia. That means the designer has to couple a motor and platter as a system. The platter is designed to be a mass damper. We use mass dampers in dynamic systems. We use mass to tune System Natural Frequencies and keep them out of certain operating ranges. A bigger platter requires a higher torque motor in order to be stable. Perhaps the youtube example is a tt design with an undersized motor. I would say as a rule of thumb, the motor in a tt should be able to accelerate the platter up to speed within one rotation. To me that would indicate that the motor has sufficient torque to maintain a stable speed. btw- I just checked my tt and it is up to speed within one rotation.

Chris,
Your wish is my command :-)
Please forgive the amateurish state of the movie but it was taken on my iphone4.....my first film..... and my first upload to utube!
TT-101