Direct drive vs belt vs rim vs idler arm

Dev,
The Raven AC does not perform as well as the TT-101 in regards to 'stylus drag' yet seems to be better than the Transrotor appears from the Timeline video?

For what it's worth though......the sound of the Raven AC can be just as musically satisfying as the Victor.

Dover,
The only visual test for 'stylus drag' using the Timeline.....is to have the turntable operating with the steady stationary flash on the wall WITHOUT the arm lowered...and then to lower the arm and see if the flashing light moves at all.
Raising and lowering the arm several times whilst observing the action of the flashing light will confirm success or failure?

Halcro -
I think your test methodology would prove that only turntables with error speed correction built in will pass. We know that stylus drag exists and should always set speed with the stylus playing. The question then becomes how significant is stylus drag variation, should we speed correct, and if so how. Remember also that the timeline is only a sampling of 1 per revolution, what is happening in between that interval is unknown.
You could have Turntable A that has a much bigger variation when dropping the stylus than turntable B but has a better instantaneous speed correction. Which is better for sound reproduction ?
We also know that the natural recovery of AC motors and Brushless DC motors if the motor "slips" due to back emf and goes out of phase slightly that the recovery is different - some say the AC motor recovers sinusoidally whereas a DC motor tends to recover trapezoidally. Can you measure this ? What difference does it make to the sound ?
Lots of unknowns here.

From Dover's post, "The point I take from your Goldmund example is that you are suggesting that mass alone will not provide stability with a motor that simply doesn't have enough torque to start with."

Let's think about this for a minute. Is the platter solid? Where is the bulk mass located? If the platter is solid, most of the mass is toward the outside, correct? Is that where it should be? One would assume that it should be because almost all turntable platters are made that way. But, it it really the right way to design a platter, regardless of the drive type?

Now, let's make some analogies.

1) You have a playground merry-go-round with six kids on it. They are positioned towards the outer rim.
2) You have a playground merry-go-round with six kids on it. They are positioned, so that the merry-go-round is perfectly balanced from center to edge.
3) You have a playground merry-go-round with six kids on it. They are positioned as close to the center as possible.

All the kids and all the merry-go-rounds weigh exactly the same. Which merry-go-round is easiest to control, if you are the guy pushing it? Would a scenario exist where it be possible for a small girl push one of them, but not the others?

I submit to you all that platter design is the most seriously overlooked aspect of a turntable. Location of mass matters, and it matters a lot. I consider the platter to be more key to the sound of a given turntable than drive type, or speed accuracy for that matter.

Disclosure: I manufacture idler drive turntables with speed controllers.

.

Halcro/Tony

I've just done the Halcro drop test of dropping the stylus on and off without adjusting the speed. The fall off in speed is minute. I would estimate it would take a couple of hours at least for the error to translate to 1 complete revolution. So according to my rudimentary maths for my TT
1.8seconds per revolution/7200 seconds ( time to complete 1 rotation error ) = a speed variation of 0.025%. Even an hour would only be 0.05%.
( Tony correct me if I'm wrong on the maths, my brain is disfunctional at the moment ).
With the speed adjusted for the tracking weight there is 0 drift.
To me the big question is how consistant is the impact of the stylus drag on speed and if error correction is used, is the bark worse than the bite. This will no doubt come back to the quality of the particular solution offered.